*Note about the audio* 🚨 Sorry for the noise gate issue! The SEM is in the same room and has two pumps running continuously (diaphragm pump + turbomolecular pump). I cover it all in acoustic material, but there is still a lot of noise to clean up. And apparently I did a bad job this time (combination of noise removal in Izotope and gating in Resolve). Apologies for the audio discomfort! I edit with headphones on, but probably went numb to it after a while and didn't notice. Luckily, it should improve soon... the SEM is moving to a new room in the near future 🙂 *Addendum* It seems I overstated how hard it is to grind and polish polymers! Several folks have informed me that e.g. eyeglasses are mostly polymers these days. I'm not sure what kind of tolerance they hold relative to glass lenses, but clearly it's a mass-produced and probably polished on-demand for each prescription. I suspect it's still a lot harder to DIY good polymer lens grinding than glass though.
Still better sounding than 90% of UA-cam videos! :) Just consider making the "release" of the gate/noise remover a bit longer or go with an expander instead and it won't be so noticeable, or even consider layering in some pink or brownian noise (or background music) back after the removal to avoid the total lack of noise. Most noise filters or multi-band expanders/gates also let you adjust the frequency band it works on the most. You can hunt down those upper-mid early reflections that are giving you the most audible trouble with overall less noise removal. Also, never forget the inverse square law: the closer you can get the mic to you and the further you can get it from the noise source, the easier your life will be in post. Likewise, if there is a specific noise source, rather than putting the mic in a traditional spot (e.g. above the head or near the camera), point it so the null of the cardioid pattern (i.e. back of the mic) is pointed directly at the noise source. You're only getting maybe -6 dB rejection on the side of the mic in the traditional arrangement, but in the null you might get -15, -20, even -30 dB through most of the audible band on a small diaphragm condenser.
If you layer a long piece of just noise floor audio from anywhere (doesn't have to be your lab) put it under your audio at like -40db to -30db it'll remove the jarryness of the audio cuts.
The definition of "home shop" seems to a bit fluid, but maybe that's just me ;) "making optical-quality surfaces [...] is really hard to do in a home shop, I don't have a single-point diamond lathe." "just sputter some silver onto your glass in your sputtering chamber..." "let's look at this under the SEM / atomic force microscope..." Just joking of course, awesome content, very interesting.
That's hilarious! ... but I think you missed the point altogether. The point is, that it is a demonstration of a guy who has these things IN HIS HOME SHOP. Of course, that gives us husbands clear proof that the best makers NEED these tools! Okay, I will admit the scanning electron microscope may be a bit pricy, and never in stock at Home Depot, so my wife can better justify a SawStop tablesaw with less bickering.
hmmm... i did a few things but improved the surface by spin coating the optical elements in a second step with resin. The layer is very thing to the spin coating but finishes the surface to much higher perfection.
@@peterjf7723 Yes, just by spinning the epoxy in a container, the surface of the epoxy would form into a perfectly parabolic shape thanks to centripetal force.
@@peterjf7723 bubbles might cause a problem with the surface and the uneven distribution of heat within the epoxy might add distortions also but i think it would be fun to see it tried out.
Me, seated on a brick as chair into a 3rd world country watching this carefully in order to make no mistakes when I have to cast precision lens with resin somehow.
Mee too, I am from India. I got photophobia so I can't work in computers for long so trying to switch in manufacturing, but I spent all my money in treating disease so I need low cost method. I managed to make and sell products but they need transparency to meet quality standards in order to sell and bring reasonable profit. What's your story bro
😂 I'm in kenya I'm trying to make AR glasses but i can't get lenses months of research has led me here god knows where I'll get this epoxy or a bloddyold
Hell beats dying from poisonous food n water from America like an American friend of mine haha she layer up in a hospital dreaming of playing with her resin. Me on the other hand is watchin this because I need one so I can stare at the sun n see what happens. Seems we’re all doing surprising random things!!! Beats paying taxes and working for any oppressor hahaha
@@CurtainsAndcarpetsEpoxy resin can be made by epoxydation of any polyphenol compound, including paper factory lignin waste or tat being the byproduct of wood pyrolysis to tar. As long as you can make epichlorohydrine from glycerol you will be able to get epoxy at least for mirror optics, and if you have a neighbor who does moonshine you can clarify epoxy a lot.
@@dollbaby9017 don't stare at the sun directly, especially not with a lens... a lens is in actuality the same thing as a magnifying glass... and we know it can burn so strong it can light fires. If you want to see the sun, you can use either solar eclipse goggles, or welding goggles/face shield. You can also use a camera to zoom in on the sun, and using the goggles in front of the camera lens to help it see without the images being washed out from too much light. Good quality resins and molding silicones are not cheap. If you need to zoom onto the sun, consider buying a second hand "super zoom" camera, which would probably only cost twice the cost of materials for casting and molds.
Very cool! The surface finish and actual shape (I forget your actual word for that) look amazing! I have to say I’m drooling at the thought of a diamond lathe for making aspheric curvatures but I’m afraid to look up the cost…
Yeah, not half bad for such a janky setup! Definitely not going to put Leica or Zeiss out of business any time soon though 😂 I did some poking around and it seems entry SPDT lathes start around 350k USD. It's not as much as I expected, but still a pretty darn expensive single-purpose, niche tool!
You have a great presence in your videos. The lack of BS and depth of technical combined with an accessible persona is great. I look forward to every video, often in topics I didn’t know I was interested in .
@ebrewste I feel the same way, thanks for putting it into words. ...And kudos for the way you did, keeping it short while capturing the essence is not easy, (at least for me:).
This was very interesting for me. I am a mechanical engineer and usually watch makers on UA-cam such as yourself so i am happy YT recommended this vid. As a person who wears glasses and get them scratched in no time, making my own lenses at home would be awesome!
You could polish the lenses before hand to remove some of the imperfections. Then you will want to spin coat a low viscosity mold release to get a smooth surface. degassing the resins premixing will let you degas it better/more gently once it is mixed. If you sputter coat the glass lens with silver as a mold release you could get a perfect surface. Since it has no silicon in it, it wont stick.
Regarding stiffness issue, maybe use a CNCed part the is "pretty" close to the lens you want, so the silicone pour you need is just a thin layer. I know you will hit the issue of silicone not adhering to this stiff base, so maybe CNC also some "holes" (|like a mesh), so silicone has a lot of mechanical grab. Really nice that you share the issues you found, I think that is the most interesting part. When things work, those are more boring ;)
I think this would help a lot! Didn't occur to me at the time, but yeah, some kind of "pre-form" I think would help to both provide mechanical support, and reduce silicone consumption (which also means it would cure more uniformly due to thinner, more consistent layers). Good idea!
As a bonus, the metal preform should act as a thermal mass and keep curing more even (and could be water-cooled much more easily than a silicone mold, I imagine)
A large fraction of epoxy problems come from incomplete mixing. If you are using wooden stirrers, cut the end square with scissors so you can scrape the sides and bottom of the mixing cup. Mix in one cup until you get tired of mixing, then transfer that to a second cup and mix again. This removes the thin layer of poorly mixed material on the walls of the first cup. Use nitrile gloves and change them when you get resin on them-- never wipe it away with solvent. Now on to how epoxy cures. Every epoxy will have a Tg, or glass transition temperature. This is the point where the cured epoxy transitions from rigid and glassy to rubbery. Tg is mostly determined by the chemical structure of the curative and the cure conditions used to cure the epoxy. A typical hardware store epoxy will be designed knowing that it is unlikely that the customer will heat cure the part. Because of this, the chemist will choose a relatively 'hot' curative that cures in reasonable time at room temperature. The Tg of hardware store epoxy will likely be 20-30C above room temperature. You may be able to increase the Tg a bit by gently heating the cured part, but you are most likely limited by the flexible chemical structure of the curative. If you move to heat cure epoxy things change. Shop for these by looking for Tg, HDT (heat deflection temperature, usually 20-40C less than Tg), or cure temperature required on the data sheet. These epoxies are likely to use a cycloaliphatic or aromatic curative, which have stiffer chemical structures and can support higher Tg. There are other high temperature curatives of course, but the trend holds. Anyway, many of these can cure to some degree at room temperature. The Tg increases to 20-30C over room temperature, but at that point the structure becomes rigid ('vitrifies'), which prevents reactive chemical groups from being able to come into contact with each other and reacting. This point is often termed a 'green cure' and with certain curatives can yield a brittle polymer. You can then heat this material, increase the number of bonds and increase the Tg to 20-30C above the curing temperature-- if the structure of the curative is stiff enough to support it. There will be a limit on Tg, imposed either by the maximum cure temperature you can achieve or by the rigidity of (usually) the curative. Home made ovens can be cheap and effective. Scaled Composites has made aircraft wings in ovens made from hardware store parts. Incandescent lights and space heaters can provide excellent heat sources, but be careful of fire. If I were trying to cast an optical lens, I would look for a high temperature laminating epoxy with a Tg in the 120-140C range. I would make sure the data sheet claimed that the resin cured clear or 'water white', which means clear. Weigh it on a scale, mix it in 2 cups, degas it and cure at room temperature. Then find a way to slowly heat it to the temperature listed on the data sheet.
@7:50 YES you can polish plastic as good as you can polish glass! You just need to use finer grit paper or less abbrasive materials and also you get the best result if you do wet sanding and then wet polish with VERY high grit sandpaper and oil or water. I do it myself so YES you can!
A small technical note, epoxy is not exactly a plastic , it is a polymer but it falls under the thermoset group. It actually doe not melt nor smears if polished. It is possible to polish it. Check any example of polished carbon fiber composite.
Hmm... i should try this. I've been making deformed lenses from cyanoacrylate. The whole point of those is to have optical quality "blobs". They give uneven ghostly images when used with RGB leds, deliberately breaking the smooth beam. As the RGB elements are slightly off set from each other, each individual led gives its own distorted image. But because they are so close to each other, you get similar shapes, for ex arc where one side is blue, one is red with a green band in the middle. When you slowly fade them out, it animates the image.. Very, very beautiful. This experimentation started from using crumpled mylar as a reflector. It just loses a lot of strength and it is difficult to get it at optimal distance. But distorting the image at the source, i get must clearer image. I add layers of cyanoacrylate, let it drip using accelerator in the other hand to freeze the shapes in place.
Would be curious if you could use a non silica glass, like CaF2 or MgF2 to avoid to silicone/silica bonding issues with the mold and not require sputter coating
While lenses made from fluorides exist, they are reasonably expensive compared to glass lenses. I imagine the simplest and cheapest way would be to buy lenses that already have some sort of coating, or spin coat and bake them yourself.
Or AR coatings. Some of which might not be too hard to sputter/evaporate so you've got a leg up on that one! (Again, give or take size of pattern/mold fitting inside the chamber.)
@@T3sl4 I mean, the matter of fact is that he actually has the necessary equipment to sputter lenses himself, so what we are all describing are ways to do it if didn't have that.
Instead of sputtering metal on to the glass lenses, you could try an oleophobic coating that once applied and then polished off leaves a nanometer-scale fluorine-based layer on the glass. Try talking to Aculon in San Diego. As you alluded to, you probably want to minimize the thickness of the silicone molds and bond them to a steel plate with cooling channels so you can actively cool the parts while curing. For the single-step molding, you can use an optical grade silicone (yes, you can make silicone lenses, I've seen a few very nice examples). A longer runner might help reduce the stress at the gate location. The chromatic aberrations you are seeing are likely caused by dispersion. The epoxy you are using likely has a high dispersion (low Abbe number). The common method of canceling dispersion is to combine high and low dispersion elements (classically this was a flint and crown glass element). Do note that your lens copies won't match the glass originals, even if you perfectly copy the form and eliminate all stresses, as the refractive index and Abbe numbers will be different from that of the glass.
What an amazing job! I'd suggest post-curing the ready lenses in an oven at about 85 Celsius before disassembling molds. This is used for ordinary epoxy in order to make it stronger, but in your case it may relieve internal stresses. The post-cure temperature is close to melting point of the epoxy. An another trick may be - create lens with say 95% of the desired thickness. Post-cure etc. Disassemble mold. Then add some epoxy on both sides, assemble and cure, post-cure. Ready. You can try to defeat shrinkage in such way.
To Stiffen Molds -Paint back of mold with a thin layer of silicone an lay on a piece of glass, let cure. /or/ -Use rat wire fencing laid on the back of the mold and paint it on with more silicone, let cure. This should stiffen it up real nice like. +chicken wire has ~3x3cm hexagons (very flexible) +rabbit wire has ~10x20cm rectangles (very stiff but big) +rat wire has 1x1cm squares (very nice) I recommend a mesh type material rather than a solid flat sheet since the silicone wont stick to many things other than itself or glass as stated in the video.
Hi Zach, nice work. I was wondering what your ultimate goal is exactly. If you want to make spherical surfaces, you should not start with a spherical mold, because then you will end up with an oblate elliptical surface, due to the volume shrink. So for making spherical surfaces, you need to start out with some kind of parabola/hyperbola. By the way, if you want to make epoxy/glass fiber mirrors of high quality (for example for telescopes), maybe reconsider: it is technically virtually impossible. I can mail you a few references if you want.
Ah yeah, that makes sense! Can account for shrinkage by adjusting the shape of the mold first. 👍 Would definitely be interested in those references! I've seen a number of papers in regards to replicated CFRP telescope mirrors and while they all highlight challenges (molding distortion, fiber print-through, differential thermal expansion, moisture absorption over time, etc) none of it appeared to be insurmountable. But perhaps once you consider all those challenges in aggregate it just becomes too hard to produce something optically good enough for a telescope? Definitely going to pretend I didn't read that it was impossible and continue trying though, haha. A guy can dream 😁
@@BreakingTaps I'll admit I have zero experience with epoxy but an idea came to me. Could you cure the epoxy at elevated pressure? I'd assume it would make the final part higher density and maybe get rid of most imperfections making it a feasible technique for optical parts. Could also help with the uneven forces on the mold.
I am a noob and I know this sounds a bit bonkers - but I wonder about some out of box approaches - thinking about how fresnel work - I wonder if building a lens or mirror - micron by micron, so you can control refractive index and chromatic aberration and internal reflection Is possible in a well appointed home shop. You and Applied Science channel could have a fun go at it !
Might be a bit out of my skillset, but there's some neat work done in this area using two-photon lithography. Basically does exactly what you said: prints them up layer by layer at a small enough scale to avoid aberrations. Check out this paper for example (open access: www.frontiersin.org/articles/10.3389/fmats.2020.586496/full ), they print lenses on the end of optical fibers. Pretty cool!
Dude you're the first to do this thank you I was wondering why no one had ever done this I looked it up months ago to see if I could do this myself but no one has ever I guess until now.
Your vids are always interesting, your production quality outstanding and your presentation is spot on. Consistently excellent and one of my favourite channels for all of those reasons!
It seems like dropping a glass backer on the freshly poured silicon would be a good combo as silicon likes to bond to glass. Also using much thinner silicon pour would reduce flexing with that technique. 3D printed mold walls with surface features to give a mechanical bond to the silicon would also aid in making a more robust mold block along with the glass backer. Assembly and injection features can also be added easily to the 3D printed mold wall. Thanks for sharing your work with us.
Since silicone bonds to glass, why not use a glass plate as a backer when you're casting the upper half of the mold? Then it would support against sag when casting the lens.
Hah, yeah I think so! Didn't think of that at all, but dropping a piece of plate glass or similar on top (or even chopped fibers into the silicone) would probably stiffen it up nicely. Will keep that in mind for future projects!
Hmm that's a good idea. I'm not sure, but probably! Not sure how durable those coatings are so it might start to degrade but if you can get a clean mold off the first time it shouldn't matter.
@@BreakingTaps Being hydrophobic, it should be fine. The AR coatings are PH sensitive though, not sure if that's an issue. I work in a digital eye lab and we use lye to strip AR coatings, but it is fairly stable in things like alcohol. You might have better luck with a composite mold with glass on the top and bottom, and silicone walls. The lens blanks we use are injection molded against precision ground glass, and then we surface the RX on the back (so every lens basically begins its life as a hockey puck). Most eyewear is made with plastics, and surface roughness and haziness is reduced with some fine polishing using aluminum hydroxide, and the varnish anti-scratch coatings cover up the rest. I wonder if you could replicate a hardcoat being spun on, though we use very high RPM's to avoid pitting. Just keep in mind that the refractive index of that epoxy must be awful even compared to the cheapo plastic CR-39 lenses, but it might actually be a step above acrylic lenses like the ones you might find with some magnifying glasses.
@@eapellow9767 👍 this is a pretty ambitious project for home gamer, some other mentions, the backside of the lens is ground with a domed tool made aluminum with about 600 to 800 grit paper stuck to it. constant flow of water. then a polishing process, which I'm gonna skip commenting on to mention. I agree coating the lens if done correctly will improve the optical quality there is spin coating and dip coating.. after a suitable "hard coatimg" try and do an anti reflective coating with the sputter process. and hydrophobic coating to protect it.. again part of those process has multiple issue to contend with but being the 2nd guy I've seen on UA-cam sputter coating in the garage and I worked in an optical lab for years i seen alot of equipment. and I know labs use them but I had never seen one (sputter coater), until UA-cam. that's awesome
This was such a good, helpful and well-researched video! No time wasted and the extra stuff such as diagrams and putting lenses through polarised light to show the tensions makes such a difference in understanding wtf is going on. Thank you!!
Have you tried detergent in water as a mold release for silicone? I've used it diluted a few hundred to one in water. spray on lightly with a plant misting sprayer and let dry before molding. It might not be good enough for your lenses, but its way better than that commercial stuff you used. I've used it to get very gloss surfaces with ogoo molding. As well as the go to thing to stop silicone products sticking to things in building industry caulking. In Caulking you can also use it on your finger to get a really smooth fillet and skin the silicone in one go. Alcohol also works in a similar way but its not great for mold release due to evaporating too fast.
There are "Solar cigarette lighters" made out of metalized plastics to light your cigarette in the sun. They aren't too bad optically and quite cheap. I tried to make a little spotlight out of one and it worked out great.
I made mirrors out of epoxy for a college project about 30 years ago. Got an old record player, and modified it. so I could control the RPM. When spun a liquid forms a parabola, so I let the epoxy set as it spun on the deck, in a shallow circular container, and behold we have an astronomical mirror. Great little experiment.
Silicone rubber is used for making statues that are big. The silicone rubber is supported by cast plaster usually after the statue is coated with rubber. Typically like a mask of a face is made. So the surface has a lot of features that the plaster can hold the shape of the rubber. So the plaster casting is removed from the rubber and then the rubber from the cast part. plaster can have cooling tubing. Actually you do not want a high thermal conductor if you can keep the heat generated by the epoxy or low. Even thick parts will tend to have uniform temperature epoxy. To plan the cooling add up the thermal conductivity of the epoxy at a tangent to the surface to the center. Add the thermal resistance of the silicone for it's thickness and then the plaster to the cooling.
This is great information, thanks for sharing! I would add that you can use acrylic resins and optically clear silicone to make lenses. Be careful not to buy acrylic that contains mercury - it's often used in cheaper products to make it clear, and it's toxic when liquid. The refractive index of plastic tends to be lower than glass, so expect the lens power to be different from the glass original. To get around the thickness problem, you could try moulding thin layers of epoxy in an open mould to gradually build up thickness. Then when the lens is almost reaching the other half of the mould, put the lid on and do the final surface with it closed as you would normally. To get rid of bubbles, you can put the entire mould inside a vacuum chamber or use a machine to vibrate the gas bubbles out.
One thing I thought of was using a 3D Printed part to model any lens, then coating it in epoxy to remove the roughness of the layer lines (AlphaPhoenix has made a video on it), and casting that in a mold. A fairly precise part without the limits of what others have already made. It also eliminates the need for a sputtering machine, as you're casting epoxy and 3-D filament, instead of glass
I managed to get limited success making lenses from epoxy without moulds or existing templates. I used a ring of plastic to hold the epoxy, sealed on the bottom with clingfilm stretched tight. To make a convex lens, add a thick layer of epoxy, seal the top and inject air or epoxy to bow the clingfilm out. Concave lenses, the air or epoxy is removed. I also had limited success injecting epoxy between two sheets of clingfilm to make both sides convex and concave, but gravity distorts them and the lower surface is always more convex than the upper. The only downsides are that they arent hugely accurate, and the clingfilm surfaces are delicate. But they work well for visual magnification, and the magnification can be tuned while injecting or removing the epoxy. Nice video, very informative. I didnt know silicone could hold an optical surface, thought it was a bit grainy...
I’ve sanded and polished resin, worked quite well. Plastic is harder to sand and polish but not impossible, just more effort and time, if it’s spun on a machine, makes it easy. If it’s spun be could fire polished like glass fire polishing.
I guess you can avoid the silicon moulding step and create your own mould by sticking some kind stretchy plastic film (like food wrap) over a container. Then introduce partial vacuum into the container. As a result you will get a concave plastic mould with a smooth surface. And the curvature of the mould can be controlled by controlling the pressure inside the container. With two of these you can get a whole mould in which you can inject the epoxy (if aligned correctly) . You can use small to medium quantity of epoxy in this short of mould as if you use a big amount of epoxy the shape of the plastic film might get distorted due to it's weight. And I assume the plastic should also come out easily. It's worth giving a try.
That's a really interesting project! I guess the biggest step is the stress-free curing of the epoxy so that you get rid of the birefringence. (just a small comment: the noise gate on your audio is a bit disturbing when listening with headphones. Don't be afraid of a bit of background noise...)
Hi sir, To make a very thick convex lens, use old incandescent bulbs for the epoxy mold. Of course, since I did not have epoxy, I filled the inside with distilled water and filled the its hole with hot glue and closed it, but the outside of the bulb glass bubble is slightly grooved and does not fit well with lens water alone, but I am sure it will become a strong spherical lens with epoxy. You can even split old light bulbs into two pieces, each of which becomes a mold to make a convex lens (flat on one side and convex on the other).
I wonder whether you would get a better result if you use very slow curing and shake the mold at a high frequency for a while to get rid of the internal stresses
Coolest channel! I love understanding these processes that are normally out of reach because they are so industrialized. Not to say that it's easy to create a great lens but understanding the principles brings me great joy!
Wow I've been looking for this kind of video for about a year. I'm trying to figure out a way to make a cheap spherical mirror with a good optical quality out of epoxy. Haven't started yet but this video will be a goldmine for this project (and I'm hyped for the one about mirrors obviously). One particular detail that catched my eye is the bubble defect at 10:20. Did you noticed how sharp the reflexion are on the bubble spot? Maybe using bubbles can solve multiple problems like: having multiple steps using silicone molds that introduce imperfections or getting a perfect spherical surface since the constraint from a gaz is usually uniform. Unfortunately I think bubbles will obviously be very sensitive to themral shrinking gaz will expand due to the epoxy warming up so it might be difficult to control but this is a nice track to keep in mind.
As for the mold release. Have you considered spin coating? I know i show up late to the game. But i figured this might do in future projects. Also, a mold release per se has only the job of preventing the two parts forming any kind of bond. So maybe the commercial mold releases are not the best choice. An (to the processes involved) inert liquide with adequate viscosity and surface adhesion might do the trick.
7:55 "You can't polish, grind, sand plastic like you can glass" - that's true which is why you polish, grind and sand epoxy resin lenses like you would do with plastic. You don't use sanding paper, you use rotary sponge with special car headlight polishing compound. You won't get glass finish with epoxy lenses but if you can apply yourself you will get a decent, low cost lens that is suitable for low magnification scopes.
I wonder if polymers can be tempered like glass is to reduce the internal stresses. Another idea that comes to mind would be to use some form of solvent polishing to post process the optical surface. Or perhaps heat can be used to flow the material after curing. Judging by the surface roughness of the bubble that you showed as a defect, you could achieve way better surface finish if you could find a way to refine the surface...
you should try the rotating mold method for creating large parabolic mirrors. observatory mirrors are sometimes made this way. they just have a huge plate that rotates at a fixed rate and they pour molten glass on it. the glass naturally forms a perfect parabola from the rotation, and hardens.
Carnauba wax, often used with polyester resin molds. Also found in some wood floor waxes of days gone by. I was scanning these posts for some mention of this. Good one!
An old unfinished mirror project of mine was spin casting epoxy on a record player (but an air bearing is probably required to reduce vibration). Newton came up with the spinning idea and experimented using mercury, plagued by bearing vibration he moved onto other interests. Cheers -Peter
There was an observatory that used a spinning mirror made by spin casting a resin backing to provide the rough shape, letting the resin cure while spinning. For the reflecting surface some Mercury was poured in then the mirror spun up to spread the metal out. The mirror assembly was mounted on a short track so it could move against Earth's rotation for a short time. The problem with such a mirror is it must be level so it can only be used to observe what passes directly over it. So to look at different stars the whole thing would need to be relocated.
This is great. Looking forward to your next video about mirrors. Do you have an end use for the mirrors? A telescope could be a really cool use for direct carbon fiber molding technique.
I was similarly curious about telescope mirrors but more for making a high-zoom compact monocular based off something like this: ua-cam.com/video/HxwhCmO90UQ/v-deo.html
Potential solution... If you take two of the exact same lens, thus, when facing each other, you have both the front and back of the lens with an airgap of any preferred distance. Encase the airgap with whatever material you may like, and fill the gap with epoxy via a syringe. A potential problem with this method would be the degree of adhesion between the selected epoxy and the glass, and if that would require the use of mold release (which we already know causes issues). Just a thought. Thank you for the great video!
Consider using Rustoleum Mirror Paint as the mold release for the resin; the paint will make a first surface mirror against the silicone, but bond to the resin when you pull it out. I think this will work because the mirror paint makes a striking second surface mirror when applied to the inside of glass. I just don’t know if you want the paint wet or dry before pouring the epoxy in…
As a mold release, how about a thin coat of hard wax like carnauba, buffed to a high shine? Used on glass or shiny metal, buffed wax creates a layer that’s completely invisible-just looks like bare glass or metal. But it’s slippery and very hydrophobic.
Maybe you could purposefully add a lot of internal stress to the lenses to make a Gradient-index lense. They use an optical density gradient rather than normal refraction, so you might not need to worry about surface quality as much? Idk. It might work especially well because you are already working with epoxies and I think you can use a uv resin and cure different parts at different speeds. It might also be extremely hard to do, but could be a fun project.
Great breakdown. Since silicone adheres to glass, you should use a thick glass surface as a backing on your molds so they hold their shape without sagging. Glass can be pretty stiff so much better than nothing.
(11:45) this is why I thought of using silicon carbide grit added to silicon rubber for tires would make an incredibly long wearing tire, as the SiC would be protruding making the contact with road surfaces while the rubber could squish down between these grits, and you would then be riding on nearly as hard as diamond needle points that would give refined surface friction, as well as removing any smoothing that has happened from regular tires polishing a road surface and making it too slick so other tires would get better grip while driving too. run this layer of SiC grit layer deep enough and you could get a tire that lasts millions of miles instead of thousands or tens of thousands of miles LOL.
Rather tough on the roads, though. I really would form a physical rut to match the functional one in my home-to-work route. But If only you and I had these gritty tires, okay. The wear would be negligible and the grip, prodigious. Unit cost of tires, also prodigious. Oh, well ... . Still, I like your thinking.
@@gemanscombe4985 yeah this is kinda why packing higher grit in around the lower grit so that normal driving would not cause such an aggressive action, unless its needed by needing to apply more effort into rotation or when sliding so the coarser grit can be pushed down around causing a more aggressive gripping and some gritting like on rough ice or something, thus instead of wearing a rut so much as a polished section of the road lol.
@@gemanscombe4985 also how do you see ruts being cut when I see people who wander all over the road so much that the road would get evenly worn down along with half a foot over the other side of those white lines on the sides or worse (saw a cop doing this for nearly 4 miles where they had drifted to the side almost to the grooved section to let you know, and were hanging out there one tire completely over the white line by nearly a foot, before they seemed to have noticed and corrected to be in between the lines
@@ThomasAndersonbsf Yup, cops can be the worst b/c they give each other breaks we would never get. "Professional courtesy", they call it. Anyway, I'd expect ruts b/c the majority of contact is made over 2 foot-wide bands that straddle the lane center, that center being demonstrated by the oil drips discoloring that part of the pavement. Certain curves and braking zones would really wear as each car's tires applied lateral and longitudinal force repeatedly and predictably. Be outstanding for winter tires and less destructive than studs.
Thanks for sharing. When I saw the first 3d printers I was instantly interested in making eye glasses. You can get the shape, but the surface roughness is far from nano-meter smooth
16:11 Before anyone throws epoxy parts in an oven, pre-cure for at least an hour at room temperature, until it seems the epoxy is no longer producing much internal heat. This will minimize the risk of a toxic, smoky oven fire from exotherm. However, take care not to disturb the part with physical stress during movement. The epoxy will be most susceptible to damage that irreversibly weakens it when mostly (but not fully) cured.
Have you tried using a firm hold hairspray instead of the mould release? It doesn't have any inclusions so _shouldn't_ leave residual marks. The hairspray will act as a mask of sorts. Alternatively (or combined), it might be possible to paint a clear enamel onto the mould, let it dry and then pour the epoxy, I saw a video just the other day where somebody was painting enamel directly on to their mould. The epoxy bonds with the enamel somehow, that's above my pay grade. If you can get the bond to occur without any seams, it might be worth trying.
Hello, do You think it would be possible to mold very fine fresnel lenses this way? Would the silicon mold and final resin cast detailed enough to behave like a fresnel lens?
While plastic lenses cannot be mechanically lapped, they can be chemically vapour polished - it is commonly used to improve surface quality on plastic lenses and is doable in home shop, basically just put lenses into flow of vapourized solvent. I'm not sure if it would work with epoxy molded lenses but is great for injection molded plastic lenses.
Could you use thermal shock as a mould release? eg put the glass/silicone in the freezer, then pour warm water on the silicone, assuming it didn't pop off already during the freezing process?
a commenter said even perfect reproduced shape won't duplicate refraction due to RI of epoxy used. If pine pitch has the same RI as optical glass when it is used to glue two elements there must be refractive indexes listed for other hardening organic moldable liquid? I recovered a round 4ft outdoor glass table top with a 2.5inch hole for an umbrella pole: i was wondering if I could slump it over a pos mold OR simply force the centre in and retain the edges to have along focal length mirror? but it seems the surface would still have to be polished right ?
This is really neat! I may actually play around with this. I actually have some smooth-on silicon and acrylic resins. Would potentially be cool to cast a lens in the inverse of the type you wanted. Say if you wanted a concave lens of a certain camber, just cast it in a convex lens of the inverse camber.
Could smooth plastic with heat, if the specific epoxy can be heat blasted. Heat does warp, but the dose makes the poison, maybe a small or calculated amount will work. _edit: the heat may also temper out the internal stresses._ I know you said you don't want to do polishing, however a very fine finishing polish may still be helpful.
You've obviously never seen the amazingly polished things people make outta epoxy resin on UA-cam, id say its not hard at all to polish, but maybe there's something i don't know about it seeing as I've only ever watched.
What about using the glass lenses themselves as part of the mold? That way you wouldn't need to worry about lenses sticking to the silicone. Does the epoxy stick to the glass and thus it wouldn't work or could the silver sputtering be used to provide a removable coating like now but again without the intermediary?
Pretty sure that's what he's doing in the "Direct molding off the mandrel" section, ua-cam.com/video/mfAGivG9Koc/v-deo.html, using the lens of opposite curvature as a mould for a mirror.
This is actually quite close to one of the techniques I'm trying with the mirrors! Epoxy... sorta sticks to the glass. It's not permanent, but it can be _very_ tenacious. I think I've ripped a few chunks out of the lens too on accident (around the edges). So some kind of mold release is still generally required, although you can play some tricks with heat to demold (freeze/thaw cycles can help break them apart since they have different expansion rates)
Most plastic lenses are, as far as I remember, made from PolyCarbonate. This is a plastic that is fairly tough, withstands UV and is kind of scratch resistant. Epoxy is prone to degrade under UV light and scratches easily. Well at least most epoxies are, there are special UV safe resins too but these are not always easy to find. That is why most carbon fiber products are either covered with a gelcoat or a clear UV filter laquer.
Off course you can we used to do it all the time we need to put samples in epoxy for the microscope , we polished them to perfection with diamond paste
Lapping something flat is a lot easier than trying to grind and polish a 3D profile (even simple ones like spherical profiles). Not saying it's impossible, just that it's considerably harder than with glass 🙂
Something I've learned long ago when it comes to cheap optics is that it's usually better to find cheaper ways to makes optics out of good materials than cheap way to makes optics out of cheap materials. There's really not a good substitute for glass, both with mirrors and lenses. What should be done instead is finding a way to build or replace glass making machines that cost less but that delivers good performance.
Are there adjuncts you can add to the epoxy to set the refractive index? Also, when the refractive index is being measured, is there a lightwavelength (or chroma) standard to do this at?
Great questions! So the answer is.... maybe. I've been looking through literature and there are some exotic chemicals you can add to epoxies to adjust their IOR, but it doesn't appear to change it _much_. There are also some papers which dope the epoxy with metal oxide nanoparticles (titanium dioxide for example). The idea is that the nanoparticles are small enough and the concentration low enough that it doesn't affect the transparency too much, but being nanoparticles they can have a big influence on refraction. I'm chasing a few leads there, we'll see. When people say the "index of refraction" as a single number, it's referring to the IOR at 589nm (yellow light). Historical quirk: it's the average of the doublet emission lines from burning sodium and folks started measuring at that wavelength. But all modern glasses have a set of constants defined which you can plug into an equation to get the IOR for any specific wavelength you care about, the single number (1.56 for my epoxy) is just shorthand to get you in the right neighborhood basically :)
@@BreakingTaps Here's a bizarre thought: If you were to 3d print plastic lenses rather than cast them, you might be able to fix chromatic aberration by adding dopants accurately to layers within the lens. It wouldn't have to be a surface coating, as I think is done with glass lenses.
Can you cover the the lens with mylar as a release material? You might be able to place the mylar under a vacuum to create the convex or concave and pour the silicone directly onto the mylar to produce the mould.
Can you reinforce your silicone molds when you create them? Add bamboo skewers or something that you leave in? It seems like a grid of them would be enough to sufficiently stabilize the mold.
There may be an issue with temperature with the larger lenses. Looks like they may have overheated a bit, which causes a wavey and hazy look to the resin. The solution would be a slower curing resin that tolerates deep pours more, but that further increases cure time.
long video is long so not sure if you are going to cover it but seems like the lenses you have could be used if coated properly to release the item, to make the opposing surface too, like having a .2 diopler of one direction and ending up with a cast lens that is a -.2 diopler lens if that is the appropriate measurement terms if not basically using a convex lens surface to get a concave lens that matches it exactly in a negative aspect. reason this thought came to me is that some times having the exact opposite of the former is needed for proper light alignment like making a true spot light out of a normal lamp, (seems like coating after too makes a good reflection surface XD
*Note about the audio* 🚨 Sorry for the noise gate issue! The SEM is in the same room and has two pumps running continuously (diaphragm pump + turbomolecular pump). I cover it all in acoustic material, but there is still a lot of noise to clean up. And apparently I did a bad job this time (combination of noise removal in Izotope and gating in Resolve). Apologies for the audio discomfort! I edit with headphones on, but probably went numb to it after a while and didn't notice. Luckily, it should improve soon... the SEM is moving to a new room in the near future 🙂
*Addendum* It seems I overstated how hard it is to grind and polish polymers! Several folks have informed me that e.g. eyeglasses are mostly polymers these days. I'm not sure what kind of tolerance they hold relative to glass lenses, but clearly it's a mass-produced and probably polished on-demand for each prescription. I suspect it's still a lot harder to DIY good polymer lens grinding than glass though.
I really appreciate the honesty, most creators would just ignore a slight issue like this. Well done !.
Still better sounding than 90% of UA-cam videos! :)
Just consider making the "release" of the gate/noise remover a bit longer or go with an expander instead and it won't be so noticeable, or even consider layering in some pink or brownian noise (or background music) back after the removal to avoid the total lack of noise.
Most noise filters or multi-band expanders/gates also let you adjust the frequency band it works on the most. You can hunt down those upper-mid early reflections that are giving you the most audible trouble with overall less noise removal.
Also, never forget the inverse square law: the closer you can get the mic to you and the further you can get it from the noise source, the easier your life will be in post. Likewise, if there is a specific noise source, rather than putting the mic in a traditional spot (e.g. above the head or near the camera), point it so the null of the cardioid pattern (i.e. back of the mic) is pointed directly at the noise source. You're only getting maybe -6 dB rejection on the side of the mic in the traditional arrangement, but in the null you might get -15, -20, even -30 dB through most of the audible band on a small diaphragm condenser.
If you layer a long piece of just noise floor audio from anywhere (doesn't have to be your lab) put it under your audio at like -40db to -30db it'll remove the jarryness of the audio cuts.
Great to see that this was noticed, it's a small thing, but it's good to see you care. I really enjoy the videos,
i do not notice it at all, listening through my speaker, even if i try to. As @Sam Gossner wrote, you sound better than many other youtubers.
The definition of "home shop" seems to a bit fluid, but maybe that's just me ;)
"making optical-quality surfaces [...] is really hard to do in a home shop, I don't have a single-point diamond lathe."
"just sputter some silver onto your glass in your sputtering chamber..."
"let's look at this under the SEM / atomic force microscope..."
Just joking of course, awesome content, very interesting.
Haha, ok that's fair 😂
I thought the same in those exact instant.
@@BreakingTaps I am just amazed by the quality of some of the home labs out there. TheThoughtEmporium is also quite amazing if it comes to home labs.
Some home shops are better than others!
That's hilarious! ... but I think you missed the point altogether.
The point is, that it is a demonstration of a guy who has these things IN HIS HOME SHOP.
Of course, that gives us husbands clear proof that the best makers NEED these tools!
Okay, I will admit the scanning electron microscope may be a bit pricy, and never in stock at Home Depot, so my wife can better justify a SawStop tablesaw with less bickering.
hmmm... i did a few things but improved the surface by spin coating the optical elements in a second step with resin. The layer is very thing to the spin coating but finishes the surface to much higher perfection.
Spin-casting should be good for making a reflective mirror. By adjusting the rotation speed you could in theory make different focal length mirrors.
@@peterjf7723 Yes, just by spinning the epoxy in a container, the surface of the epoxy would form into a perfectly parabolic shape thanks to centripetal force.
@@poptartmcjelly7054 I wonder how good the optical would be.
Could you expand on this just a smidge, it sounds interesting. Are you spin coating the pattern/mandrel, the mold or the part?
@@peterjf7723 bubbles might cause a problem with the surface and the uneven distribution of heat within the epoxy might add distortions also but i think it would be fun to see it tried out.
Me, seated on a brick as chair into a 3rd world country watching this carefully in order to make no mistakes when I have to cast precision lens with resin somehow.
Mee too, I am from India. I got photophobia so I can't work in computers for long so trying to switch in manufacturing, but I spent all my money in treating disease so I need low cost method. I managed to make and sell products but they need transparency to meet quality standards in order to sell and bring reasonable profit. What's your story bro
😂 I'm in kenya I'm trying to make AR glasses but i can't get lenses months of research has led me here god knows where I'll get this epoxy or a bloddyold
Hell beats dying from poisonous food n water from America like an American friend of mine haha she layer up in a hospital dreaming of playing with her resin. Me on the other hand is watchin this because I need one so I can stare at the sun n see what happens. Seems we’re all doing surprising random things!!! Beats paying taxes and working for any oppressor hahaha
@@CurtainsAndcarpetsEpoxy resin can be made by epoxydation of any polyphenol compound, including paper factory lignin waste or tat being the byproduct of wood pyrolysis to tar. As long as you can make epichlorohydrine from glycerol you will be able to get epoxy at least for mirror optics, and if you have a neighbor who does moonshine you can clarify epoxy a lot.
@@dollbaby9017 don't stare at the sun directly, especially not with a lens... a lens is in actuality the same thing as a magnifying glass... and we know it can burn so strong it can light fires. If you want to see the sun, you can use either solar eclipse goggles, or welding goggles/face shield. You can also use a camera to zoom in on the sun, and using the goggles in front of the camera lens to help it see without the images being washed out from too much light.
Good quality resins and molding silicones are not cheap. If you need to zoom onto the sun, consider buying a second hand "super zoom" camera, which would probably only cost twice the cost of materials for casting and molds.
Very cool! The surface finish and actual shape (I forget your actual word for that) look amazing! I have to say I’m drooling at the thought of a diamond lathe for making aspheric curvatures but I’m afraid to look up the cost…
You can probably get a monocrystaline diamond cutter from china fairly cheap, then any cnc lathe will do a good enough job to test things
Yeah, not half bad for such a janky setup! Definitely not going to put Leica or Zeiss out of business any time soon though 😂 I did some poking around and it seems entry SPDT lathes start around 350k USD. It's not as much as I expected, but still a pretty darn expensive single-purpose, niche tool!
@@BreakingTaps Take a look at Huygens Optics channel.
@@BreakingTaps I won't call it cheap but I was expecting, at least, one more zero on the price.
Yeah I was really expecting the same!
You have a great presence in your videos. The lack of BS and depth of technical combined with an accessible persona is great. I look forward to every video, often in topics I didn’t know I was interested in .
@ebrewste I feel the same way, thanks for putting it into words.
...And kudos for the way you did, keeping it short while capturing the essence is not easy, (at least for me:).
This was very interesting for me. I am a mechanical engineer and usually watch makers on UA-cam such as yourself so i am happy YT recommended this vid. As a person who wears glasses and get them scratched in no time, making my own lenses at home would be awesome!
You could polish the lenses before hand to remove some of the imperfections. Then you will want to spin coat a low viscosity mold release to get a smooth surface. degassing the resins premixing will let you degas it better/more gently once it is mixed. If you sputter coat the glass lens with silver as a mold release you could get a perfect surface. Since it has no silicon in it, it wont stick.
Regarding stiffness issue, maybe use a CNCed part the is "pretty" close to the lens you want, so the silicone pour you need is just a thin layer. I know you will hit the issue of silicone not adhering to this stiff base, so maybe CNC also some "holes" (|like a mesh), so silicone has a lot of mechanical grab.
Really nice that you share the issues you found, I think that is the most interesting part. When things work, those are more boring ;)
Was going to suggest this. Reducing amount of error the silicone can introduce may reduce overall error.
I think this would help a lot! Didn't occur to me at the time, but yeah, some kind of "pre-form" I think would help to both provide mechanical support, and reduce silicone consumption (which also means it would cure more uniformly due to thinner, more consistent layers). Good idea!
i was going to comment that theres no way a CNC he could get would be able to produce a mirror finish but i realized i read the comment wrong. :(
As a bonus, the metal preform should act as a thermal mass and keep curing more even (and could be water-cooled much more easily than a silicone mold, I imagine)
A large fraction of epoxy problems come from incomplete mixing. If you are using wooden stirrers, cut the end square with scissors so you can scrape the sides and bottom of the mixing cup. Mix in one cup until you get tired of mixing, then transfer that to a second cup and mix again. This removes the thin layer of poorly mixed material on the walls of the first cup. Use nitrile gloves and change them when you get resin on them-- never wipe it away with solvent.
Now on to how epoxy cures. Every epoxy will have a Tg, or glass transition temperature. This is the point where the cured epoxy transitions from rigid and glassy to rubbery. Tg is mostly determined by the chemical structure of the curative and the cure conditions used to cure the epoxy. A typical hardware store epoxy will be designed knowing that it is unlikely that the customer will heat cure the part. Because of this, the chemist will choose a relatively 'hot' curative that cures in reasonable time at room temperature. The Tg of hardware store epoxy will likely be 20-30C above room temperature. You may be able to increase the Tg a bit by gently heating the cured part, but you are most likely limited by the flexible chemical structure of the curative. If you move to heat cure epoxy things change. Shop for these by looking for Tg, HDT (heat deflection temperature, usually 20-40C less than Tg), or cure temperature required on the data sheet. These epoxies are likely to use a cycloaliphatic or aromatic curative, which have stiffer chemical structures and can support higher Tg. There are other high temperature curatives of course, but the trend holds. Anyway, many of these can cure to some degree at room temperature. The Tg increases to 20-30C over room temperature, but at that point the structure becomes rigid ('vitrifies'), which prevents reactive chemical groups from being able to come into contact with each other and reacting. This point is often termed a 'green cure' and with certain curatives can yield a brittle polymer. You can then heat this material, increase the number of bonds and increase the Tg to 20-30C above the curing temperature-- if the structure of the curative is stiff enough to support it. There will be a limit on Tg, imposed either by the maximum cure temperature you can achieve or by the rigidity of (usually) the curative. Home made ovens can be cheap and effective. Scaled Composites has made aircraft wings in ovens made from hardware store parts. Incandescent lights and space heaters can provide excellent heat sources, but be careful of fire.
If I were trying to cast an optical lens, I would look for a high temperature laminating epoxy with a Tg in the 120-140C range. I would make sure the data sheet claimed that the resin cured clear or 'water white', which means clear. Weigh it on a scale, mix it in 2 cups, degas it and cure at room temperature. Then find a way to slowly heat it to the temperature listed on the data sheet.
@7:50 YES you can polish plastic as good as you can polish glass! You just need to use finer grit paper or less abbrasive materials and also you get the best result if you do wet sanding and then wet polish with VERY high grit sandpaper and oil or water. I do it myself so YES you can!
A small technical note, epoxy is not exactly a plastic , it is a polymer but it falls under the thermoset group. It actually doe not melt nor smears if polished. It is possible to polish it. Check any example of polished carbon fiber composite.
Hmm... i should try this. I've been making deformed lenses from cyanoacrylate. The whole point of those is to have optical quality "blobs". They give uneven ghostly images when used with RGB leds, deliberately breaking the smooth beam. As the RGB elements are slightly off set from each other, each individual led gives its own distorted image. But because they are so close to each other, you get similar shapes, for ex arc where one side is blue, one is red with a green band in the middle. When you slowly fade them out, it animates the image.. Very, very beautiful.
This experimentation started from using crumpled mylar as a reflector. It just loses a lot of strength and it is difficult to get it at optimal distance. But distorting the image at the source, i get must clearer image. I add layers of cyanoacrylate, let it drip using accelerator in the other hand to freeze the shapes in place.
Do you have video clips of this? Sounds amazing ^^
Agreed, please share some images / videos / words on the process!
Dang, I need to see the resulting images of this
I worked for years in a surface lab lapping and polishing plastic lenses all day. It's absolutely practical
Would be curious if you could use a non silica glass, like CaF2 or MgF2 to avoid to silicone/silica bonding issues with the mold and not require sputter coating
Oh, I hadn't even thought of non-silica glass. That's a very interesting idea!
While lenses made from fluorides exist, they are reasonably expensive compared to glass lenses. I imagine the simplest and cheapest way would be to buy lenses that already have some sort of coating, or spin coat and bake them yourself.
Or AR coatings. Some of which might not be too hard to sputter/evaporate so you've got a leg up on that one! (Again, give or take size of pattern/mold fitting inside the chamber.)
@@T3sl4 I mean, the matter of fact is that he actually has the necessary equipment to sputter lenses himself, so what we are all describing are ways to do it if didn't have that.
@@graealex Well, ZnSe lenses are a thing and actually somewhat cheap since they're used for CO2 cutters
Instead of sputtering metal on to the glass lenses, you could try an oleophobic coating that once applied and then polished off leaves a nanometer-scale fluorine-based layer on the glass. Try talking to Aculon in San Diego.
As you alluded to, you probably want to minimize the thickness of the silicone molds and bond them to a steel plate with cooling channels so you can actively cool the parts while curing.
For the single-step molding, you can use an optical grade silicone (yes, you can make silicone lenses, I've seen a few very nice examples).
A longer runner might help reduce the stress at the gate location.
The chromatic aberrations you are seeing are likely caused by dispersion. The epoxy you are using likely has a high dispersion (low Abbe number). The common method of canceling dispersion is to combine high and low dispersion elements (classically this was a flint and crown glass element).
Do note that your lens copies won't match the glass originals, even if you perfectly copy the form and eliminate all stresses, as the refractive index and Abbe numbers will be different from that of the glass.
What an amazing job!
I'd suggest post-curing the ready lenses in an oven at about 85 Celsius before disassembling molds. This is used for ordinary epoxy in order to make it stronger, but in your case it may relieve internal stresses. The post-cure temperature is close to melting point of the epoxy.
An another trick may be - create lens with say 95% of the desired thickness. Post-cure etc. Disassemble mold. Then add some epoxy on both sides, assemble and cure, post-cure. Ready. You can try to defeat shrinkage in such way.
To Stiffen Molds
-Paint back of mold with a thin layer of silicone an lay on a piece of glass, let cure. /or/
-Use rat wire fencing laid on the back of the mold and paint it on with more silicone, let cure.
This should stiffen it up real nice like.
+chicken wire has ~3x3cm hexagons (very flexible)
+rabbit wire has ~10x20cm rectangles (very stiff but big)
+rat wire has 1x1cm squares (very nice)
I recommend a mesh type material rather than a solid flat sheet since the silicone wont stick to many things other than itself or glass as stated in the video.
Hi Zach, nice work. I was wondering what your ultimate goal is exactly. If you want to make spherical surfaces, you should not start with a spherical mold, because then you will end up with an oblate elliptical surface, due to the volume shrink. So for making spherical surfaces, you need to start out with some kind of parabola/hyperbola. By the way, if you want to make epoxy/glass fiber mirrors of high quality (for example for telescopes), maybe reconsider: it is technically virtually impossible. I can mail you a few references if you want.
Ah yeah, that makes sense! Can account for shrinkage by adjusting the shape of the mold first. 👍
Would definitely be interested in those references! I've seen a number of papers in regards to replicated CFRP telescope mirrors and while they all highlight challenges (molding distortion, fiber print-through, differential thermal expansion, moisture absorption over time, etc) none of it appeared to be insurmountable. But perhaps once you consider all those challenges in aggregate it just becomes too hard to produce something optically good enough for a telescope?
Definitely going to pretend I didn't read that it was impossible and continue trying though, haha. A guy can dream 😁
@@BreakingTaps I'll admit I have zero experience with epoxy but an idea came to me. Could you cure the epoxy at elevated pressure? I'd assume it would make the final part higher density and maybe get rid of most imperfections making it a feasible technique for optical parts. Could also help with the uneven forces on the mold.
Great to see some favorite optics guys know each other...
I am a noob and I know this sounds a bit bonkers - but I wonder about some out of box approaches - thinking about how fresnel work - I wonder if building a lens or mirror - micron by micron, so you can control refractive index and chromatic aberration and internal reflection
Is possible in a well appointed home shop. You and Applied Science channel could have a fun go at it !
Might be a bit out of my skillset, but there's some neat work done in this area using two-photon lithography. Basically does exactly what you said: prints them up layer by layer at a small enough scale to avoid aberrations. Check out this paper for example (open access: www.frontiersin.org/articles/10.3389/fmats.2020.586496/full ), they print lenses on the end of optical fibers. Pretty cool!
Sweet! I was just riffing- sounds like I have some fun homework!
@@BreakingTaps The link is broken - love your community engagement, keep it up :)
@@karim1485 Fixed, thanks for the ping!
Dude you're the first to do this thank you I was wondering why no one had ever done this I looked it up months ago to see if I could do this myself but no one has ever I guess until now.
I'm glad you decided to make and upload this video even though you didn't perfect it. Love the video format!
Your vids are always interesting, your production quality outstanding and your presentation is spot on.
Consistently excellent and one of my favourite channels for all of those reasons!
It seems like dropping a glass backer on the freshly poured silicon would be a good combo as silicon likes to bond to glass. Also using much thinner silicon pour would reduce flexing with that technique. 3D printed mold walls with surface features to give a mechanical bond to the silicon would also aid in making a more robust mold block along with the glass backer. Assembly and injection features can also be added easily to the 3D printed mold wall.
Thanks for sharing your work with us.
Since silicone bonds to glass, why not use a glass plate as a backer when you're casting the upper half of the mold? Then it would support against sag when casting the lens.
seems like glass would be a good backing material since it bonds to it, and it can be pretty rigid
Hah, yeah I think so! Didn't think of that at all, but dropping a piece of plate glass or similar on top (or even chopped fibers into the silicone) would probably stiffen it up nicely. Will keep that in mind for future projects!
Can you use a lens with anti-reflection coating (MgF) to prevent sticking of silicone?
Hmm that's a good idea. I'm not sure, but probably! Not sure how durable those coatings are so it might start to degrade but if you can get a clean mold off the first time it shouldn't matter.
@@BreakingTaps Being hydrophobic, it should be fine. The AR coatings are PH sensitive though, not sure if that's an issue. I work in a digital eye lab and we use lye to strip AR coatings, but it is fairly stable in things like alcohol. You might have better luck with a composite mold with glass on the top and bottom, and silicone walls. The lens blanks we use are injection molded against precision ground glass, and then we surface the RX on the back (so every lens basically begins its life as a hockey puck). Most eyewear is made with plastics, and surface roughness and haziness is reduced with some fine polishing using aluminum hydroxide, and the varnish anti-scratch coatings cover up the rest. I wonder if you could replicate a hardcoat being spun on, though we use very high RPM's to avoid pitting. Just keep in mind that the refractive index of that epoxy must be awful even compared to the cheapo plastic CR-39 lenses, but it might actually be a step above acrylic lenses like the ones you might find with some magnifying glasses.
@@eapellow9767 👍 this is a pretty ambitious project for home gamer, some other mentions, the backside of the lens is ground with a domed tool made aluminum with about 600 to 800 grit paper stuck to it. constant flow of water. then a polishing process, which I'm gonna skip commenting on to mention. I agree coating the lens if done correctly will improve the optical quality there is spin coating and dip coating.. after a suitable "hard coatimg" try and do an anti reflective coating with the sputter process. and hydrophobic coating to protect it.. again part of those process has multiple issue to contend with but being the 2nd guy I've seen on UA-cam sputter coating in the garage and I worked in an optical lab for years i seen alot of equipment. and I know labs use them but I had never seen one (sputter coater), until UA-cam. that's awesome
This was such a good, helpful and well-researched video! No time wasted and the extra stuff such as diagrams and putting lenses through polarised light to show the tensions makes such a difference in understanding wtf is going on. Thank you!!
Have you tried detergent in water as a mold release for silicone? I've used it diluted a few hundred to one in water. spray on lightly with a plant misting sprayer and let dry before molding. It might not be good enough for your lenses, but its way better than that commercial stuff you used.
I've used it to get very gloss surfaces with ogoo molding. As well as the go to thing to stop silicone products sticking to things in building industry caulking. In Caulking you can also use it on your finger to get a really smooth fillet and skin the silicone in one go.
Alcohol also works in a similar way but its not great for mold release due to evaporating too fast.
Loving your content so far. I can see your channel growing exponentially in the near future!
this channel is a goldmine for people who like people making stuff
There are "Solar cigarette lighters" made out of metalized plastics to light your cigarette in the sun. They aren't too bad optically and quite cheap. I tried to make a little spotlight out of one and it worked out great.
I made mirrors out of epoxy for a college project about 30 years ago.
Got an old record player, and modified it. so I could control the RPM. When spun a liquid forms a parabola, so I let the epoxy set as it spun on the deck, in a shallow circular container, and behold we have an astronomical mirror.
Great little experiment.
Silicone rubber is used for making statues that are big. The silicone rubber is supported by cast plaster usually after the statue is coated with rubber. Typically like a mask of a face is made. So the surface has a lot of features that the plaster can hold the shape of the rubber. So the plaster casting is removed from the rubber and then the rubber from the cast part. plaster can have cooling tubing. Actually you do not want a high thermal conductor if you can keep the heat generated by the epoxy or low. Even thick parts will tend to have uniform temperature epoxy. To plan the cooling add up the thermal conductivity of the epoxy at a tangent to the surface to the center. Add the thermal resistance of the silicone for it's thickness and then the plaster to the cooling.
Absolutely loving your content. Keep it coming!
The carbon fiber mirror idea is excellent. Thanks for sharing the knowledge you gained with us, for free.
Spdt sounds really cool, didn't know how those molds were made, this channel is amazing
Thanks!
This is great information, thanks for sharing! I would add that you can use acrylic resins and optically clear silicone to make lenses. Be careful not to buy acrylic that contains mercury - it's often used in cheaper products to make it clear, and it's toxic when liquid. The refractive index of plastic tends to be lower than glass, so expect the lens power to be different from the glass original. To get around the thickness problem, you could try moulding thin layers of epoxy in an open mould to gradually build up thickness. Then when the lens is almost reaching the other half of the mould, put the lid on and do the final surface with it closed as you would normally. To get rid of bubbles, you can put the entire mould inside a vacuum chamber or use a machine to vibrate the gas bubbles out.
I didn't expect this much knowledge and experience from a YT video, this is a paper worthy type of information
One thing I thought of was using a 3D Printed part to model any lens, then coating it in epoxy to remove the roughness of the layer lines (AlphaPhoenix has made a video on it), and casting that in a mold. A fairly precise part without the limits of what others have already made. It also eliminates the need for a sputtering machine, as you're casting epoxy and 3-D filament, instead of glass
I managed to get limited success making lenses from epoxy without moulds or existing templates. I used a ring of plastic to hold the epoxy, sealed on the bottom with clingfilm stretched tight. To make a convex lens, add a thick layer of epoxy, seal the top and inject air or epoxy to bow the clingfilm out. Concave lenses, the air or epoxy is removed. I also had limited success injecting epoxy between two sheets of clingfilm to make both sides convex and concave, but gravity distorts them and the lower surface is always more convex than the upper.
The only downsides are that they arent hugely accurate, and the clingfilm surfaces are delicate. But they work well for visual magnification, and the magnification can be tuned while injecting or removing the epoxy.
Nice video, very informative. I didnt know silicone could hold an optical surface, thought it was a bit grainy...
Thanks
I’ve sanded and polished resin, worked quite well. Plastic is harder to sand and polish but not impossible, just more effort and time, if it’s spun on a machine, makes it easy. If it’s spun be could fire polished like glass fire polishing.
I guess you can avoid the silicon moulding step and create your own mould by sticking some kind stretchy plastic film (like food wrap) over a container. Then introduce partial vacuum into the container. As a result you will get a concave plastic mould with a smooth surface. And the curvature of the mould can be controlled by controlling the pressure inside the container. With two of these you can get a whole mould in which you can inject the epoxy (if aligned correctly) . You can use small to medium quantity of epoxy in this short of mould as if you use a big amount of epoxy the shape of the plastic film might get distorted due to it's weight. And I assume the plastic should also come out easily. It's worth giving a try.
That's a really interesting project!
I guess the biggest step is the stress-free curing of the epoxy so that you get rid of the birefringence.
(just a small comment: the noise gate on your audio is a bit disturbing when listening with headphones. Don't be afraid of a bit of background noise...)
Hi sir, To make a very thick convex lens, use old incandescent bulbs for the epoxy mold. Of course, since I did not have epoxy, I filled the inside with distilled water and filled the its hole with hot glue and closed it, but the outside of the bulb glass bubble is slightly grooved and does not fit well with lens water alone, but I am sure it will become a strong spherical lens with epoxy.
You can even split old light bulbs into two pieces, each of which becomes a mold to make a convex lens (flat on one side and convex on the other).
I wonder whether you would get a better result if you use very slow curing and shake the mold at a high frequency for a while to get rid of the internal stresses
Coolest channel! I love understanding these processes that are normally out of reach because they are so industrialized. Not to say that it's easy to create a great lens but understanding the principles brings me great joy!
Wow I've been looking for this kind of video for about a year. I'm trying to figure out a way to make a cheap spherical mirror with a good optical quality out of epoxy. Haven't started yet but this video will be a goldmine for this project (and I'm hyped for the one about mirrors obviously).
One particular detail that catched my eye is the bubble defect at 10:20. Did you noticed how sharp the reflexion are on the bubble spot? Maybe using bubbles can solve multiple problems like: having multiple steps using silicone molds that introduce imperfections or getting a perfect spherical surface since the constraint from a gaz is usually uniform. Unfortunately I think bubbles will obviously be very sensitive to themral shrinking gaz will expand due to the epoxy warming up so it might be difficult to control but this is a nice track to keep in mind.
As for the mold release. Have you considered spin coating? I know i show up late to the game. But i figured this might do in future projects. Also, a mold release per se has only the job of preventing the two parts forming any kind of bond. So maybe the commercial mold releases are not the best choice. An (to the processes involved) inert liquide with adequate viscosity and surface adhesion might do the trick.
I'm so jealous of you on so many levels!!!
Thumbs up from Montréal!
Hey! Great video! I'm glad you liked the metal coating for mold release trick from the micro lenses video!
🤗
7:55 "You can't polish, grind, sand plastic like you can glass" - that's true which is why you polish, grind and sand epoxy resin lenses like you would do with plastic. You don't use sanding paper, you use rotary sponge with special car headlight polishing compound. You won't get glass finish with epoxy lenses but if you can apply yourself you will get a decent, low cost lens that is suitable for low magnification scopes.
I am not going to make any lenses today but i definitely learned a lot! Brilliant video!!
So chill, I made one of these for my Rink building maintenance refrigeration engineering book, so I can magnify things around the arena!
I wonder if polymers can be tempered like glass is to reduce the internal stresses.
Another idea that comes to mind would be to use some form of solvent polishing to post process the optical surface. Or perhaps heat can be used to flow the material after curing. Judging by the surface roughness of the bubble that you showed as a defect, you could achieve way better surface finish if you could find a way to refine the surface...
you should try the rotating mold method for creating large parabolic mirrors. observatory mirrors are sometimes made this way. they just have a huge plate that rotates at a fixed rate and they pour molten glass on it. the glass naturally forms a perfect parabola from the rotation, and hardens.
You can re-enforce large moulds with glass fibers to stiffen them or even enclose them in a hard shell.
As a mould release for silicone i can recomend hard car wax. Very simple but effective.
Carnauba wax, often used with polyester resin molds. Also found in some wood floor waxes of days gone by. I was scanning these posts for some mention of this. Good one!
I remember the good ol days when we didn't have no e-bikes or e-mail we certainly didn't have any fancy e-poxy.
Great vid
An old unfinished mirror project of mine was spin casting epoxy on a record player (but an air bearing is probably required to reduce vibration). Newton came up with the spinning idea and experimented using mercury, plagued by bearing vibration he moved onto other interests.
Cheers -Peter
There was an observatory that used a spinning mirror made by spin casting a resin backing to provide the rough shape, letting the resin cure while spinning. For the reflecting surface some Mercury was poured in then the mirror spun up to spread the metal out. The mirror assembly was mounted on a short track so it could move against Earth's rotation for a short time. The problem with such a mirror is it must be level so it can only be used to observe what passes directly over it. So to look at different stars the whole thing would need to be relocated.
This is great. Looking forward to your next video about mirrors. Do you have an end use for the mirrors? A telescope could be a really cool use for direct carbon fiber molding technique.
I too am excited about your next mirror episode ... As I have a 50 year old telescope to remirror
I was similarly curious about telescope mirrors but more for making a high-zoom compact monocular based off something like this: ua-cam.com/video/HxwhCmO90UQ/v-deo.html
For those who don't have the equipment for chemical vapor deposition, Tollen's Reagent can be used to silver the mirror using a chemical bath.
Potential solution... If you take two of the exact same lens, thus, when facing each other, you have both the front and back of the lens with an airgap of any preferred distance. Encase the airgap with whatever material you may like, and fill the gap with epoxy via a syringe. A potential problem with this method would be the degree of adhesion between the selected epoxy and the glass, and if that would require the use of mold release (which we already know causes issues). Just a thought. Thank you for the great video!
Consider using Rustoleum Mirror Paint as the mold release for the resin; the paint will make a first surface mirror against the silicone, but bond to the resin when you pull it out.
I think this will work because the mirror paint makes a striking second surface mirror when applied to the inside of glass.
I just don’t know if you want the paint wet or dry before pouring the epoxy in…
You're really thorough and knowledgeable with a soothing voice. Subbed.
As a mold release, how about a thin coat of hard wax like carnauba, buffed to a high shine? Used on glass or shiny metal, buffed wax creates a layer that’s completely invisible-just looks like bare glass or metal. But it’s slippery and very hydrophobic.
Maybe you could purposefully add a lot of internal stress to the lenses to make a Gradient-index lense. They use an optical density gradient rather than normal refraction, so you might not need to worry about surface quality as much? Idk. It might work especially well because you are already working with epoxies and I think you can use a uv resin and cure different parts at different speeds. It might also be extremely hard to do, but could be a fun project.
Love your content mate. Would be interesting to hear what you do in your day job and how you got started!
Great breakdown. Since silicone adheres to glass, you should use a thick glass surface as a backing on your molds so they hold their shape without sagging. Glass can be pretty stiff so much better than nothing.
(11:45) this is why I thought of using silicon carbide grit added to silicon rubber for tires would make an incredibly long wearing tire, as the SiC would be protruding making the contact with road surfaces while the rubber could squish down between these grits, and you would then be riding on nearly as hard as diamond needle points that would give refined surface friction, as well as removing any smoothing that has happened from regular tires polishing a road surface and making it too slick so other tires would get better grip while driving too.
run this layer of SiC grit layer deep enough and you could get a tire that lasts millions of miles instead of thousands or tens of thousands of miles LOL.
Rather tough on the roads, though. I really would form a physical rut to match the functional one in my home-to-work route. But If only you and I had these gritty tires, okay. The wear would be negligible and the grip, prodigious. Unit cost of tires, also prodigious. Oh, well ... . Still, I like your thinking.
@@gemanscombe4985 yeah this is kinda why packing higher grit in around the lower grit so that normal driving would not cause such an aggressive action, unless its needed by needing to apply more effort into rotation or when sliding so the coarser grit can be pushed down around causing a more aggressive gripping and some gritting like on rough ice or something, thus instead of wearing a rut so much as a polished section of the road lol.
@@gemanscombe4985 also how do you see ruts being cut when I see people who wander all over the road so much that the road would get evenly worn down along with half a foot over the other side of those white lines on the sides or worse (saw a cop doing this for nearly 4 miles where they had drifted to the side almost to the grooved section to let you know, and were hanging out there one tire completely over the white line by nearly a foot, before they seemed to have noticed and corrected to be in between the lines
@@ThomasAndersonbsf Yup, cops can be the worst b/c they give each other breaks we would never get. "Professional courtesy", they call it. Anyway, I'd expect ruts b/c the majority of contact is made over 2 foot-wide bands that straddle the lane center, that center being demonstrated by the oil drips discoloring that part of the pavement. Certain curves and braking zones would really wear as each car's tires applied lateral and longitudinal force repeatedly and predictably. Be outstanding for winter tires and less destructive than studs.
Thanks for sharing. When I saw the first 3d printers I was instantly interested in making eye glasses. You can get the shape, but the surface roughness is far from nano-meter smooth
Absolutely fascinating discussion. Thanks.
Eyyy
16:11 Before anyone throws epoxy parts in an oven, pre-cure for at least an hour at room temperature, until it seems the epoxy is no longer producing much internal heat. This will minimize the risk of a toxic, smoky oven fire from exotherm. However, take care not to disturb the part with physical stress during movement. The epoxy will be most susceptible to damage that irreversibly weakens it when mostly (but not fully) cured.
Have you tried using a firm hold hairspray instead of the mould release?
It doesn't have any inclusions so _shouldn't_ leave residual marks.
The hairspray will act as a mask of sorts.
Alternatively (or combined), it might be possible to paint a clear enamel onto the mould, let it dry and then pour the epoxy, I saw a video just the other day where somebody was painting enamel directly on to their mould.
The epoxy bonds with the enamel somehow, that's above my pay grade.
If you can get the bond to occur without any seams, it might be worth trying.
you could use gypsum (stone or die stone) to make the mold. Find out more about how dental technicians make molds or casts to a microlevel.
Hello, do You think it would be possible to mold very fine fresnel lenses this way? Would the silicon mold and final resin cast detailed enough to behave like a fresnel lens?
While plastic lenses cannot be mechanically lapped, they can be chemically vapour polished - it is commonly used to improve surface quality on plastic lenses and is doable in home shop, basically just put lenses into flow of vapourized solvent. I'm not sure if it would work with epoxy molded lenses but is great for injection molded plastic lenses.
Could you use thermal shock as a mould release? eg put the glass/silicone in the freezer, then pour warm water on the silicone, assuming it didn't pop off already during the freezing process?
a commenter said even perfect reproduced shape won't duplicate refraction due to RI of epoxy used. If pine pitch has the same RI as optical glass when it is used to glue two elements there must be refractive indexes listed for other hardening organic moldable liquid?
I recovered a round 4ft outdoor glass table top with a 2.5inch hole for an umbrella pole: i was wondering if I could slump it over a pos mold OR simply force the centre in and retain the edges to have along focal length mirror? but it seems the surface would still have to be polished right ?
Never thought of using sputtering on resin lenses. Genius
This is really neat! I may actually play around with this. I actually have some smooth-on silicon and acrylic resins. Would potentially be cool to cast a lens in the inverse of the type you wanted. Say if you wanted a concave lens of a certain camber, just cast it in a convex lens of the inverse camber.
Could you polish plastic lenses if you chill them to cryogenic temperature first, and keep them cool throughout the polishing process?
Thought this too
Could smooth plastic with heat, if the specific epoxy can be heat blasted.
Heat does warp, but the dose makes the poison, maybe a small or calculated amount will work.
_edit: the heat may also temper out the internal stresses._
I know you said you don't want to do polishing, however a very fine finishing polish may still be helpful.
Hi. I would like to know more about the cf mirrors. Could you tell us about how it is going? And what is that grey stuff you spread over the glass?
i think you and ben would make a unstoppable youtube combo.
You've obviously never seen the amazingly polished things people make outta epoxy resin on UA-cam, id say its not hard at all to polish, but maybe there's something i don't know about it seeing as I've only ever watched.
What about using the glass lenses themselves as part of the mold? That way you wouldn't need to worry about lenses sticking to the silicone.
Does the epoxy stick to the glass and thus it wouldn't work or could the silver sputtering be used to provide a removable coating like now but again without the intermediary?
Pretty sure that's what he's doing in the "Direct molding off the mandrel" section, ua-cam.com/video/mfAGivG9Koc/v-deo.html, using the lens of opposite curvature as a mould for a mirror.
This is actually quite close to one of the techniques I'm trying with the mirrors! Epoxy... sorta sticks to the glass. It's not permanent, but it can be _very_ tenacious. I think I've ripped a few chunks out of the lens too on accident (around the edges). So some kind of mold release is still generally required, although you can play some tricks with heat to demold (freeze/thaw cycles can help break them apart since they have different expansion rates)
Most plastic lenses are, as far as I remember, made from PolyCarbonate. This is a plastic that is fairly tough, withstands UV and is kind of scratch resistant.
Epoxy is prone to degrade under UV light and scratches easily. Well at least most epoxies are, there are special UV safe resins too but these are not always easy to find. That is why most carbon fiber products are either covered with a gelcoat or a clear UV filter laquer.
Off course you can we used to do it all the time we need to put samples in epoxy for the microscope , we polished them to perfection with diamond paste
Lapping something flat is a lot easier than trying to grind and polish a 3D profile (even simple ones like spherical profiles). Not saying it's impossible, just that it's considerably harder than with glass 🙂
Something I've learned long ago when it comes to cheap optics is that it's usually better to find cheaper ways to makes optics out of good materials than cheap way to makes optics out of cheap materials. There's really not a good substitute for glass, both with mirrors and lenses. What should be done instead is finding a way to build or replace glass making machines that cost less but that delivers good performance.
Please Try making Monolithic Telescopes! Awsome content 🔥🔥🔥
Are there adjuncts you can add to the epoxy to set the refractive index? Also, when the refractive index is being measured, is there a lightwavelength (or chroma) standard to do this at?
Great questions! So the answer is.... maybe. I've been looking through literature and there are some exotic chemicals you can add to epoxies to adjust their IOR, but it doesn't appear to change it _much_. There are also some papers which dope the epoxy with metal oxide nanoparticles (titanium dioxide for example). The idea is that the nanoparticles are small enough and the concentration low enough that it doesn't affect the transparency too much, but being nanoparticles they can have a big influence on refraction. I'm chasing a few leads there, we'll see.
When people say the "index of refraction" as a single number, it's referring to the IOR at 589nm (yellow light). Historical quirk: it's the average of the doublet emission lines from burning sodium and folks started measuring at that wavelength. But all modern glasses have a set of constants defined which you can plug into an equation to get the IOR for any specific wavelength you care about, the single number (1.56 for my epoxy) is just shorthand to get you in the right neighborhood basically :)
@@BreakingTaps Here's a bizarre thought: If you were to 3d print plastic lenses rather than cast them, you might be able to fix chromatic aberration by adding dopants accurately to layers within the lens. It wouldn't have to be a surface coating, as I think is done with glass lenses.
2 questions:
Is it possible to polish epoxy lens?
Have you put the mold inside a vacuum chamber in order to avoid bubbles forming?
Can you cover the the lens with mylar as a release material? You might be able to place the mylar under a vacuum to create the convex or concave and pour the silicone directly onto the mylar to produce the mould.
Your videos are inspiring. Thanks for doing what you do.
Can you reinforce your silicone molds when you create them? Add bamboo skewers or something that you leave in? It seems like a grid of them would be enough to sufficiently stabilize the mold.
There may be an issue with temperature with the larger lenses. Looks like they may have overheated a bit, which causes a wavey and hazy look to the resin. The solution would be a slower curing resin that tolerates deep pours more, but that further increases cure time.
long video is long so not sure if you are going to cover it but seems like the lenses you have could be used if coated properly to release the item, to make the opposing surface too, like having a .2 diopler of one direction and ending up with a cast lens that is a -.2 diopler lens if that is the appropriate measurement terms if not basically using a convex lens surface to get a concave lens that matches it exactly in a negative aspect.
reason this thought came to me is that some times having the exact opposite of the former is needed for proper light alignment like making a true spot light out of a normal lamp, (seems like coating after too makes a good reflection surface XD