He FOUGHT his Boss over this! - Pierson Workholding Q&A - Vacuum Workholding
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- Опубліковано 1 сер 2024
- This debate over vacuum workholding got heated!
✅ How to hold flat parts a vise can't 👉 bit.ly/3n6n6WN
In this Pierson Workholding Q&A, Jay gets the question, "Does adding grooves in a top plate increase vacuum pressure?" After an employee fought over this question with his boss. He did some of his own tests and got interesting results. Jay clears the air and sets everything straight in this episode.
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00:00 Do groove in a vacuum chuck help?
00:38 Machinist question & situation
01:42 My answer
06:05 The best hack
#CNC #Machining #PiersonWorkholding - Наука та технологія
the acting in this is phenomenal
Oscar material!
Grooves are a manifold. You need them on larger parts to make up for the leak past the seals, which gets worse as the surface get rougher. We have very large vacuum fixtures for aircraft fairings and groove at least all around the seals for that reason. If you don't you will see a pressure gradient as the air rushes past the seals faster than it Can make it to the pump through the very shallow path.
Not sure if you're gonna see this, but shouldn't the only factor that matter is CFM of the pump vs the CFM of the leak? I believe you're saying the grooves act as "vacuum reservoirs", which would help if there was some immediate force trying to kick the part off the vacuum table. There is more volume to survive an instantaneous injection of air. But if there is a consistent leak where leak CFM > pump CFM, then the leak will eventually win (just a little bit slower). On the flip side, having no grooves means you can suck down big parts easier since you're sucking way less air out.
Friction (gripping force) is proportional to force not to pressure. Cars have grooves to force the water out and slick racing tyres work through an adhesive mechanism of friction which is proportional to surface area. I think it is more likely that the grooves he added reduced the resistance to the vacuum pump allowing it to combat a leaky gasket more effectively.
I tested this by making my vac fixture without any clearance between the part and plate. I just made the grooves for the O-ring and the vac port leaving a facemilled surface. I put a part on the fixture, pulled 27"s of vacuum, and then pushed the part off the fixture without much effort. Next I cut .005" of clearance in my plate leaving the minimum of islands to support my part, put a part on, pulled 27"s of vacuum, and tried to push the part off, but wasn't able to. After this test I concluded you do want some clearance between the part and vac plate as it does make a big difference in how well you hold your parts. The part was a 9" x 12" sheet of 3/4" thick polyethelene. I do love vacuum workholding but think custom fixtures made specifically for the part is the only way to go. Or start with a big flat plate with one vac port in the middle and cut some rubber sheet to fit your part and go. This is my go to for short runs but you will need a higher flow pump and larger coolant separating tank as this method doesn't seal as well as O-rings.
I don’t think your analysis of the reason why smaller contact area = higher gripping force is correct. You’re right of course that the normal force acting on the part and plate increases as the contact area decreases, but that’s balanced by area itself obviously decreasing at the same rate,. Overall, net force of friction should stay the same.
To a pretty good order of approximation, frictive forces are solely a function of the applied normal force (the force pressing the two objects together) and the coefficient of friction between them.
Consider this (long-winded) example: We have a 1,000-lb block of steel sitting on a piece of sandpaper glued to the bench. (I’m using sandpaper here to get away from any questions about vacuum and reduce it to simply a matter of friction.) Let’s say for the sake of argument that this results in a “holding force” of 500 lbs, meaning we have to press against the side of the block with 500 lbs of force to make it move. Now, let’s cut the part in half. Nothing else has changed, so we’d now have to push against either half with 250 lbs of force to get it to move. Now take one of the pieces and stack it on top of the other one, and try moving the stack. Compared to the case where the two pieces were each sitting on the sandpaper, the force between the bottom block of the stack and the sandpaper is now 2x, so the force required to move it would be 2x that needed for a single sub-block, meaning 2 x 250, and back to our original 500 lbs.
But I totally believe the truth of your observation that chucks with grooves (meaning smaller surface area in contact with the parts) grip slightly better! (!)
That means that the coefficient of friction between the part and the chuck is changing for some reason.
I don’t know enough about the subject to say why for sure, but here’s a maybe-plausible guess: It’s not just a simple three-part system (part/air/chuck); an important fourth piece is (drumroll, please ;-) ... coolant fluid!
Watching some of your automatIon videos, I was actually surprised that the parts stuck to the chuck as well as they did, without careful cleaning to get all the slippery coolant off of them first. I think what’s happening is that there’s always a very thin film of coolant between the part and the chuck, even when clamped together. At a nano-scale, that film will reduce the number of microscopic points of contact between the two pieces. (This is after all how lubricants work :-)
A liquid film is a _whole_ lot harder to move around than air, and if the mating surfaces are large and smooth, it’s gonna be very difficult for the coolant film in the middle of the part to be squeezed out. On the other hand, if the chuck has lots of grooves in it, two things happen, the second likely much more important than the first. Taking your example of a chuck face with half the surface area taken up by grooves, 1) The local forces acting to squeeze out the coolant are going to be doubled and 2) the coolant in the thin film will have *much* smaller distances to travel on average to escape the chuck/part interface.
I think this is what’s going on. There’s no simple equation to calculate how much the gripping force might increase with grooves, because it’s an incredibly complex problem with lots of variables. (Coolant chemistry, it’s viscosity, the temperature (which will affect the viscosity), the material types and surface finishes of the chuck and part, etc, etc.) But I think the above probably explains why you see the slight increase in gripping power with a grooves chuck face.)
(Great videos, BTW, and huge congrats on your great success! I’m only a hobbyist with a hand-cranked hobby-mill and still saving up for the lathe of my dreams. But I love learning about machining, and appreciate and admire how you’ve built your business, from the perspective of a former small business owner in an entirely different field for 20 years :-)
Everything you stated is correct, in theory. However, there's more at work than theory here! Workpieces and chuck surfaces have imperfections much like sand or water on a road. Tire treads channel these imperfections into the grooves and the net force of friction is the same. At the same time, the soft rubber tread is bearing a higher load and is better able to conform to the rough texture of the road. It is the imperfections of the chuck and workpiece being forced together that increase the mechanical connection between the two. That's why the sandpaper technique works so well - the sand particles are forced into the surface of the part to create a mechanical connection decreasing the role of friction.
@@PiersonWorkholding With respect sir, I also think that your explanation at the end of the video is not quite correct.
What is holding the part sideways on the chuck is the friction force, which is created from the perpendicular downward force resulting from the athmospheric pressure pushing onto the part.
Both forces are connected trough the friction coefficient.
The friction coefficient for a material pair, expresses how much of the perpendicular force is "translated" into friction force.
I you say sand paper particles are forced into the surface of the part, thats correct. But exactly that effect is desribed with the friction coefficient. The material pair sandpaper-aluminium would have a very high friction coefficient. Thats all..
If you say that groves improve holding force, i believe you, through lack of better knowledge.
But as for the explanation of the reason: I think it has been already stated in comments, that groves probably improve airflow from the suction nozzle to every part of the vacuum chuck, thus allowing for a better vacuum over the entire plate, resulting in more friction force at the end. If there are no groves, the volume of low pressure air below the part is very small. Every tiny leak will fill that volume up to ambient pressure, very fast, resulting in less friction force. However if the volume of low pressure air below the part is high, through groves, small leakes cannot easily have an influence on the pressure below the part :)
Anyway, thanks for the very well produced video and interesting points :) Happy to hear your opinion and a wish a nice day.
@@unrealillusion87 A physics teacher will say that friction is only a function of the coefficient of friction (i.e. the type materials in use) and the normal force. However that can be off in both directions. For example weak materials may rip before they get to that limit (that is part of why large tiers are used in some cases). OTOH rough surfaces may be able to geometrically grip the part, but only if the contact pressure is high enough to deform the one surface around the other. E.g. pieces of plywood with ball bearings between them: at low pressure things roll (a low coefficient of friction because the contact angel is very shallow and very little of the normal force can be translated into restraining force). However at high pressures, the balls embed into the surface and things are much different (a high coefficient of friction because the contact angel is very steep and all of the normal force, and then some, can be translated into restraining force).
Very nice, thorough breakdown. The only other thing I was expecting to pop up is that the multiplier 14 comes from the fact that 1 atmosphere of pressure is roughly 14psi and that "vacuum" kind of isn't the holding force, it's really the force of the atmospheric pressure pushing down that you gain by removing the atmospheric pressure pushing up.
Yes, you got it!
i prefer to think of it as the weight of the world is what holds it in place....
We find that flexible materials will create a seal close to the vacuum hole that causes loss of vacuum on the outer edges. A channels or multiple vacuum holes resolve this issue.
Correct. Soft materials (non metallic) can self-gasket. To prevent this, machine an X groove that intersects at the vacuum inlet hole.
I respectfully disagree. If your part has any flex (and since you use vacuum chuck to begin with, it almost always does) your tool may lift a corner high enough for the air to seep in. If you were using a grid pattern, that air will be quickly removed and the part stay in place. If you have a flat area, then your air inlet will be closed off by the rest of the part and there is not enough flow to suck the part back down. This will result in your part flying.
I honestly have to agree with you. I ran 2 Haas VF5s (1 standard, 1 Super Speed) with solid permanent aluminum 2" thick vaccum tables on them, with a 1" spacing grid pattern for 3 years daily (plastics & composites machining). I used custom vaccum subplate fixtures on top of this table, and always tried to use a single pc of gasket for each gasket seal in the grid.
When prototyping new vaccum subplates, adding shallow grooves inside the form of the final part held- the more evenly they radiated from the center of the part, and the more vaccum holes through I could get, the better the parts resisted facing pressure of the specialized flycutter we used for facing that was several inches in diameter.
I'd usually face sheets of UHMW, or even stiff Nylon to 0.01" thick skin to the table, to cut parts out with a utility knife like cookies in a sheet- but when using no grooves in subfixtures- the part would sometimes lift up just a tiny amount- and get pulled out under cutting force. Adding grooves, leaving 50-70% solid, the parts always stayed dead solid. If it picked up an edge, it might lift a corner a tiny amount, but the rest stayed dead flat instead of flying out. I was methodical every setup for 3 years testing variance in gasket density and grid patterns- having more through holes so suction could reach maximum quicker (closer to instantaneously) and the ratio of the grooves and putting seal and 1st grooves very near outline of part made the best holddown imho. Gasket durometer strength makes a big difference too, depending on how brittle or soft the material is when you cut thin.
There's lots of variables- but I think you are correct about how grooves actually affect the holddown- I never saw it as "more force" with them- just "ability for full force to instantaneously reach any area quickly" as more the way I'd describe the action to it. I feel that's correct because on rare instances the fixture itself left unblocked in except for vac holddown force could still move a fixture with part solid slightly under facing pressure (though I didn't normally leave them like this). Because all things were equal, cutting force on both, the only difference moving it if something went wrong further being the ungrooved part breaking vaccum easier, I came to think this way. My bosses thought I was nuts too- but my results always spoke for themselves well.
There's some valuable vac chuck work methodology in that it took 3 years to learn- I think it can be applied to any kind of vac chuck (including multi axis ones...) Hope that helps somebody. #instamachinists forum hiya :)
Yes, I have found this to be the case as well. You need any air under the part to have a quick path to get pulled out of there. The machined area helps with a less-than-ideal seal or situation.
@HSMAdvisor You're saying the exact same thing I mentioned at 3:23, but in a different way. A grid pattern acts like a large reservoir, two textured surfaces act like a small reservoir and two smooth surfaces create molecular reservoirs. With smooth surfaces, the time factor needs to be added so that the restricted airflow created by the vacuum can overcome the leak created by the part lifting.
@@PiersonWorkholding What I am saying is. With a smooth surface and flexy part, once you get ANY air leak through the seal, the part is basically out the window. There is no recovering it. because the central inlet hole is closed off by the center of the part that is still contacting the plate
Excellent break down on the topic!
Idea for some content: I would like to see data from pull testing on this. This is would be an easy question to answer and would only take a simple pull test fixture that could be made in the shop.
Make two fixtures: one with groves and one without. Pull them apart and record how much force it takes. You could also test for different variables. A twisting side load could be interesting to test as well.
Good to know! Thanks for the info.
Nice and in depth!
Great info!
Love the tips Jay!
Also if using coolant, which leaks past the seals, a flat surface will come off in no time at all because liquid moves a lot worse on the "molecular level". I don't see a reason why small grooves would not be made, but they don't need to be like the gasket grooves.
What a great video!
Your explanation pretty much matches mine except for one thing, which I actually thought you'd mention and somewhat alluded to in your video - a groove pattern or some sort of deeper channel can help the pump evacuate areas far from the vacuum port more quickly than without it. When I'm designing vacuum fixtures (and I use them a lot) I always have some grooves leading from the vac. port to the extremes of the fixture farthest from the port. I find that I get much more reliable clamping force and this is especially helpful if you have a low CFM pump.
When I saw the non-grooved plate sitting by your right side, it looked like there was an "X" groove leading from the center of the fixture where the port is to the extreme corners of the fixture and I thought for sure you'd mention something about it.
Have you considered not using vacuum fixtures? As a machinist, I despise them. Finicky, unreliable, seems like a cheap excuse for a desk jockey engineer to work around fixturing.
@@jerryherrin6470 , I probably should have mentioned that I do 99% of my CNC work making guitar parts on CNC routers. For necks and fretboards, vacuum fixturing works well, especially the way I do it (but I have had failures). I've never used vacuum on my mill!
@@beerco667 That makes sense. I just used to work at a shop where if someone couldn't figure out a way to fixture something they'd automatically go to the vacuum, and it was always terrible on the mills. I've seen things jump around .02", material slung across machines, and carbide just shatter. Then again, we had terrible systems so maybe my experience is jaded ;)
Another thing that a customer of mine does is they serrate the surface of their chuck as the parts can be a little dust/dirty/oily and that gives somewhere for that stuff to go. This lets the part actually get into contact with the chuck and sit flat. The operation that they are doing is very tight tolerance thickness on thin sheet metal so they have to make sure they are sitting flat other wise they scrap the part. They used to wipe down every piece but then that's down to the operator to do it good every time and as we all know that's a weak link. Now they just have to blow down the chuck once and a while so that to much crap doesn't build up on it.
I really can't believe the last part of the video is right. Friction-Forces on a flat objekt are totaly independent of the size of the contactarea! This is basic physics. (Assuming the downward force in total being the same)
Also you are assuming, that the gasket is 100% perfekt, which it never can be. My guess, why channels help, is the following: As the flow of air between the two flat serfaces is very low, the air which comes in through the gasket makes a difference. This leads to a good vakuum close to the Hole, but a weaker vakuum, the closer you get to the gasket. You can avoid this by adding some channels or a less smoth surface.
You make the same point we mention at 6:06.
Gentleman and a scholar
It helps if there’s any kind of leaks or anything it helps air to move faster I will continue to put grooves
regardless
OMFG I'm dying laughing seeing my words lip-synched by those guys and read by you. I do kinda sound like that... lol. Very unexpected (I think this was from a year ago). I think that 'top plate' part was added though ;)
Our email exchange was 90% of the script! - JP
Im enjoying my first chuck here in canada! Thanks for the great affordable product! - Leckie
I actually got help from Jay back in 2013. Ended up solving a delicate polished aluminum surface problem - our problem was that the 2nd op for an architectural product needed to have polished aluminum facing down onto the vac table. The vacuum was pulling aluminum off of the face and appeared like pitting.
The answer : sand paper.
Yah I installed a small sheet of 200grit sand paper faced down to stand the part off of the vacuum table face. Yes we still had to cut a groove for the o ring material. But it worked great.
awesome vid
The larger the hollow space underneath the workpiece, the stronger the holding force. Obviously a part needs material underneath to support it. There needs to be a fine balance of grooves and support material. Mostly depending on the pump. This is because there will always be leaks due to variance in flatness and leaks within the vacuum system. Look up Festo vacuum workholding calculations.
Yes! As a guy who has been around vacuum work before you’re company made its success, the grooves are 100% for places to put a gasket. A grooved out table is a job shopping quick setup table. A top place like you make are for specific part/job runs. None of which pull more vacuum
One thing to add about groves is this, if you are machining a porous material, I.E. wood, groves will most likely be required to keep the part held down as the you will need a constant flow of vacuum to evacuate the air being pulled through the part.
Recently made a fancy one off vacuum fixture for a decorative wood slipper sole. Did add a grid pattern in vac area and wasn't sure if I should have.
After reading your comment, makes me wonder if they are helping considering some soles grain structures or surface qualities took a few seconds for the red plunger to lower, and it doesn't fully sit flush but close.
@@GENcELL2014 the Pierson vac doesn't move enough air for doing large wooden work pieces. if its under about 5"x5" it should be ok. we use them on our lathes for vac work holding.
that said groves are a must for wood so you made the right call. got to give that vac room to suck!
@@charliebrumfield9200 decorative slippers sole is around 4.75"x11". My SmartVac3 easily developed a strong vacuum. It's for facing side2 and engraving a signature, done with a cnc router.
I learned from your UR automation videos. Thank you. Can we see more videos on UR robot? Is there a reason why you have stopped making videos using the robot?
Hey, This is some great info but still confused. I have a small CNC machine for milling wood. I created a vacuum table in Fusion 360 with square patterns to the size of my bed (being 600mm x 760mm) on the outside of the square pattern I have my gasket. I'm using melamine (non-porous) for the vacuum bed and screwing MDF (which is porous) on top of the bed. The inlet for the vacuum on the vacuum bed is center rear. I was on the notion that the grooves in the square pattern would be the path for the vacuum to hold down the MDF and whatever size of stock I'd place on the MDF board since it is porous would hold my stock. Do you think this will work for me for any size stock part regardless of the vacuum pump requirement? Thank you
Interesting, that makes sense but I never would’ve figured that. Thanks!!!!
In some cases if thin pieces with rather soft surfaces are hold down, it can happen that the part bends and creates its own seal right around the Vakuumport. Then the vacuum applies to just a very tiny area and the holding force is not sufficient. Groves prevent this from happening. So there is no definitive answer if grooves or not, always depends on the usecase. But I agree, rigid parts usally dont need grooves.
This is what I was dealing with, and Jay brought it up in my discussion with him too. I only machine plastic, and most of the plastic I work with is soft enough to self-seal around a single hole (I sometimes make vacuum fixtures with no gasket at all because of this). In general now, I basically make a pocket toolpath with a 200% step-over, and machine .010 deep, just to prevent the problem of the material sealing the vacuum in one spot.
I’m really impressed at how well this video series is done. It’s great! As an additional feature, you should track an incoming order through the material purchasing department, shipping and receiving, scheduling, programming, fabrication, quality control, and crating. People would understand your videos much better if they could place the various issues in context.
So it is a down force versus side force thing.
Funny, I had the same debate with my boss. :)
Deconstructing the mysteries of vacuum work holding........it is hard to see vacuum, air pressure, friction. I guess knowledge is the weapon of choice. :-)
The analogy of the racing tires leaves out horse power over friction. The same applies to using a vacuum chuck when you put in “tool cutting pressure”. That is only a small thing, but the details add up. And up cut end mill adds to the problem. I tried using an O ring for a seal on my parts to help with a seal. I tried all kinds of materials. What worked the best for a seal material was a silicone blend from Australia. Later, I went to no gasket at all. In short there are millions of ways to do the same thing. Find one that works the best for what your application is and run with it safely.
@John Holmes I'm in Australia, any chance you could share where you got the silicon blend from?
@@activegrip hi, I wish I could. I have been retired for about eight years now and all those records have now been shredded. I did find that company online. The Douro meter was in the 40 to 50 range if memory strikes me right. It was very soft. I got a much better seal without an o ring. The vacuum and the friction generated kept my part secure enough. I used 6061 cast aluminum plate, one inch thick. Then, I ran a face cutter to ensure the fixture was as flat as possible then I hand sanded it to remove any tooling marks to help my seal.
I wish I could be more helpful, but that is everything I have for now. Good luck to you....🤠
So it's a pressure vs. "weight". Correct? You increase the pressure by using the same weight (force) on a smaller area. Is that right?
Pressure is a constant and doesn't change. You can consider it "weight" because it's the weight of a column of air pressing down on the part. The islands bear more of the downward pressure of the part.
Halving the surface contact area of a smooth surfaces contact does NOT double holding power. Simple surface friction is F=u*N. The force is the multiplication of the surface friction, u, and the normal force applied to the surface, N. Area is not a factor in the friction forces so long as you have similar conditions. If you reduce contact area so much that now the plate started gouging or digging into the surface the simplified friction equations no longer apply and how much holding force you have is much more difficult to estimate.
Pro Tip: Research "material asperity" for a better understanding.
@@PiersonWorkholding Oh you mean surface roughness? Which has little to no impact on friction coefficients until you get to ultra high polishing? Like how gauge blocks ring together. You are nowhere close to having a smooth enough surface to get that kind of effect with typical tooling plates.
@@PiersonWorkholding Pro Tip: The Archard Wear equation used to model asperity friction also has no terms in it for pressure. Only has terms for force applied. Which,again like in simple friction, you get to because the pressure and surface area units will cancel down to simply the force applied.
Thank you for all the wonderful comments, I was looking for something like this. I am baffled by lack of knowledge of 5th grade physics and " pro's " arrogance...by his logic I just wasted money on buying bigger machinist vices, when I could just reduced contact surface of jaws by 50%...
So, basically, the grooves do help?
I'd lean toward adding grooves. Does the depth matter?
Depth doesn't matter but keep it shallow enough where gasket can't mistakenly be placed in the groove.
hi, is it possible to order SmartVac3 with shipping to Europe (Poland)? regards, Andrew
Yes, we ship daily all over the world via your choice of UPS or DHL.
Groovy was big in the 1970's but not fully appreciated until 2020's !
Hello, I know this video is two years old, but I thought that this law of physics might be interesting to you if you don’t know it already.
Friction
Although the friction force depends on the normal force, the second law of friction says that friction force does NOT depend on the area of contact between the object and the surface. Imagine if you turned a box so that less of it was touching the floor. Would that change the normal force? No! The box still weighs the same, so the normal force doesn't change, even if the area of contact does
All good points you make. The more scientific term in this application would be "asperity" but no one knows that term so I just used friction as a term people could relate to.
Boss vs Employee
3
2
1
Fight!
a lot of punching
KO!
but i dont know who won?
Lol. It did get a little heated, but didn't come to blows :)
I think everyone got the vacuum basics right, but that doesn't explain why it didn't work in practice in this case (only make mention of it like AeroGarage). Imperfect work piece surface conditions, gasket improperly sealing, cutting operation sequence details, physical limitation of the vacuum work holding systems. For example, if the vacuum power is not enough to evacuate air if a small opening is created somehow, you could buy a better vacuum system, but a grid pattern to reduce vacuum power demands during operation is most likely more practical.
Think about Einstein's quote, We cannot solve our problems with the same level of thinking that created them.
For people saying there is no difference in a grid pattern than a flat surface. Yeah the Normal force from the air outside stays the same, but look in the limit of just having a sharp pyramid supporting the piece on the bottom, what will happen? It will apply the force to the tip and drive it in the work piece. Clearly a different situation is created under the part where all that force is now applied to a single point.
Not sure how some say there is no change in frictional force using better threading. The threading allows for better traction, translating in more force applied to driving forward than is lost through heat or moving the surface material etc. by slipping. In a perfect world where you don't have slipping it doesn't matter. But 2 different things are happening to the threads in case of slipping or driving.
So in a nut shell groves make for better holding power.
You can't go wrong with extra grooves unless it deforms your part.
@@PiersonWorkholding I had the privilege to work at AMT Aerospace in Arlington, Wa and I was part of the crew loading and unloading Material onto 4’X8’ Makino Mag 3 cells Pallet tables and all their Pallets had Crisscrossed Grooves in them and they weren’t for the Vacuum Seal.
✅ How to hold flat parts a vise can't 👉 bit.ly/3n6n6WN
I'd call it a draw.
Touche'
I like this video but don't want it to be added to my liked videos... sorry bro can't throw you the like!
No problem. We're not short on likes. You should start a playlist called "Like but don't like"!
I think The end was a Little bs
Completely off topic reference to tires ?!?
It all comes down to coefficient of friction not the surface area
(As far as I know ;) )
The argument being half area double „pressure per area“ just means it’s the same ....
Double the pressure on half the area causes the texture of the materials to deform into each other causing a mechanical, not frictional connection. That's why the sandpaper method works so well.
@@PiersonWorkholding so you want to tell me that sandpaper-Metal has the same coefficient of friction as flat metal-metal surfaces ? I doubt it
But yeah the sandpaper tip is nice
@@GrafRucola Coefficient of friction is not the main principle at play here. Think of it this way. Two meshing gears have very smooth teeth to reduce friction, but they are linked mechanically. It's the same concept but at a microscopic level when the sandpaper (or any other texture) is mechanically pressed into the work piece.
@@PiersonWorkholding i think thats the definition of friction, how much surfaces interlink