AC Servo Spindle Motor, 3D Printed Mounts, DMM DYN4, PM25 Mill
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- Опубліковано 7 лют 2025
- An AC servo motor (DMM Tech DYN4) replaces the stock BLDC spindle motor on a LinuxCNC retrofitted Precision Matthews PM-25MV milling machine. Video shows 3D printed motor mount, keyway broaching on a lathe, and initial testing. Second video will be of the aluminum mount, timing belt and pulleys, and the electrical. 3D printing motor mounts could bootstrap a spindle motor replacement in an emergency.
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This was tremendously helpful as I'm in the throes of converting my Weiss VM32 mill to CNC with a Bergerda 1.5Kw servo motor for the spindle.
Very nice! I recently made a different motor mount and make a pulley from scratch to get more RPM on mine. I do most aluminum milling at 4700 rpm now, on the stock motor. It drops a couple hundred RPM at the start of a cut then surges up to 4900 or so at the end of a cut. More power would be nice, but more RPM along with it would be even better! I love your videos, thanks for taking the time to make and share!
Thank you! I'm checking out your videos, they are cool, got to love UA-cam! My PM25 is from three years ago or so. The driver board is unpotted. There's a second board that's only a filter and 5VDC supply. There are two potentiometers on the drive board. I don't remember how this works, but I'm pretty sure that one controls the upper end speed. Might be something to check out. The one thing that I wished that drive had is a fault indicator. Could mate a phototransistor to the fault light. Other than the firmware of the STC uc, the drive seems potentially repairable if anything ever went wrong. There's a post on CNC Zone where someone checked into the bearings of the PM25:
www.cnczone.com/forums/benchtop-machines/124038-wmd30-bf30-belt-drive-5000rpm-6.html#post960615
Hello Kent. Nice conversion. 3D printed parts come in handy, not only for prototyping. I am waiting for affordable 3D metal printers to be available for our kind of jobs and shops :) Thx for showing your conversion.
Hi Stefan, metal 3d printers would be so awesome! I didn't have the metal stock for this mounts, and there's something about the in-the-hand sanity check. I wonder what your thoughts are here: for a prototype would milling these from a dense wood would have been a better choice? The dimensions are more likely to be spot on, no delamination or warping, and the g-code would be tested once before cutting metal. The 3d printing is pretty cool because it demonstrates that in a pinch, like the spindle motor dies, one could make a replacement to bootstrap a better solution. But if one has a working system, perhaps prototyping essentially adapter plates in wood would be better.
@@kentvandervelden Hello Kent, dense wood (e.g. hickory, ash, beech), would probably work as well (dimensional, stability), but cutting it on a mill that has oiled or greased guides very likely will be problematic (fine wood dust will stick to the rails/bearings). Also, working with "wet" mist systems some wood types could react in combination with metal surfaces (acidic: corrosion, oxidization), that could cause issues especially on precision surfaces.
As it relates to 3D plastic prints, Stefan (not me) - ua-cam.com/channels/iczXOhGpvoQGhOL16EZiTg.html and twitter.com/cnc_kitchen - does some interesting research on how strong 3D prints are: strength as a function of cooling, vapor smoothing, layer height, infill, print material ect. If you don't know his channel, I recommend to have a look ... and they can be strong. I also saw other youtubers, using 3D printed parts as patterns/fingers to bend sheet metal at quite some volumes :)
@@stefanhertweck Thank you, your advice makes a lot of sense, and good explanation for needing a CNC router. A few days ago I found CNC Kitchen by accident, when checking out vapor smooth these parts for strength, and have been binge watched a few times :) Very interesting work.
Well done! I especially appreciate how you filmed each step. This can't be easy nor efficient when your trying to get something done. Very inspiring for someone who loves machining as much as quality UA-cam videos.
Thank you, I really appreciate this. There's always a tripod leg to trip over and never enough table surfaces :)
I like the key keyway broaching I've never done it like that ..........I've removed a fair amount of pullies but never with a heat gun good idea..... you make all these things look easy
I watched Dad remove many pulleys, with a torch :)
Video 2, creating the aluminum motor mounts: ua-cam.com/video/RgH1gKRSH0k/v-deo.html
The use of 3D printed motor mounts is probably a bit sketchy, but in an emergency might just be enough.
nice broaching!! I just did the same thing on my mill when I was building my belt grinder.
I need to rewatch that; I love the grinder you made. The idea to use the lathe for broaching came from my dad who told me about a man at work, decades ago, using a huge lathe to do an emergency broaching job. We use what we have :)
@@kentvandervelden I got that idea from clough42. I used his g-code too which worked well except there was one line of code missing. It needed a line with a "%" at the end. Here's one of his videos on it. ua-cam.com/video/cRve86xZbrw/v-deo.html
you know what you doing, it was very clear . i envy you your lathe ;)
I trust you've seen Dan Gelbart's awesome lathe? I could see you building one of this style.
ua-cam.com/video/sFrVdoOhu1Q/v-deo.html
@@kentvandervelden very tempting. but with a kid might be a very long process. who knows maybe in the future ;)
@@PiotrFoxWysocki As tired as I am all the time, I would not trade the father experience for anything! :) My Little Man turns the lathe dials and says he's "making nuts for Big Boy" (a Union Pacific big steam train)
@@kentvandervelden LOL! i have dozen of pics of both my sons cleaning up the lathe meticulously.. For some odd reason it's a big magnet for them. (and for Pjotr as well, so it seems ;-) Being tired due to the lack of sleep goes away Kent. While getting older, you'll manage just fine with less sleep. (**,)
Oh, and I should be clear. The sag in RPM is only on fast, deep, slotting cuts with a 6mm end mill. Normal clearing, boring, facing are all fine. It's just when I bury the 6mm end mill in a 9-10mm deep slot and cut full width at 500mm/min or so that the rpm drops and surges.
A clamp meter can monitor current when pushing drive to avoid exceeding rated power. I mention this only because I had a few times when pushing the stock motor that the power exceeded 1.1kW. When calculating power, The power factor changes from ~.5 idling to ~.7 when under load. I saw your cuts, they are impressive.
@@kentvandervelden Thanks! I suppose if I burn this motor up (or the board) then that forces my hand on getting a more powerful motor! :) FWIW, I broke a ton of HSS and carbide end mills on aluminum before I ordered a set of the 6mm speed tiger 3 flute off Amazon. Wow, what a difference. I even got some 3 flute generic carbide (supposedly for aluminum) off banggood, and I have not used anything like the Speed Tiger. No comparison.
I went on their website and deciphered the giant catalog where they show recommended speeds and feeds and started at about half what they were showing and worked my way up. I haven't broken one except when doing something stupid, and now use them exclusively in 6,4, and 3mm. I am cutting aluminum at higher rates with deeper cuts. It still seems too good to be true. From what I've seen the Alupower yg-1 is similar, but I have no experience with those.
Nice and quick conversion! My experience with isolating motors with either plastic or wood (MDF was the weapon of choice when converting the BF20) is that the motors tend to heat up quick if they can't get rid of their heat through the direct conductivity of an aluminum/steel mount. Was the conversion done because the need of more torque or a gain in RPM's? They very cool thing about a quick change with an indexed spindle is rigid tapping. That can be a time saver.
Hi Rene! Yes, a documented motor, with more speed, torque, and a programming interface. The brake is not enough for tool changes. The motor gets warm, but hopefully good enough for bootstrapping. The timing belt and pulleys are on their way and then will try to rigid tap. The motors are both 750W so no dramatic improvements in metal removal rates is expected. Mostly to try something different :)
Great conversion! One thing that always puzzled me was your decision to buy a motor with a brake. Would you be able to shed some light on this decision?
Hi Justin, I thought the brake may be enough to hold the spindle when changing a tool; it's not. The brake could still be helpful during broaching (though more is likely accomplished by using position servoing.) There's also a small additional amount of safety that comes from the brake, which activates during an e-stop. Would I get a brake again? Maybe not for a spindle, or for x- or y-axes, but definitely for a z-axis (and absolute encoders, likely battery backed up, for all.)
@@kentvandervelden thank you for the information! I'm currently planning a CNC conversion and find your videos very helpful.
@@justinmoritz6543 I know what you're saying: You see what NOT to do :) Feel free to send me an email if it would help. I know they are expensive, but assuming you have a similar size mill or lathe, if you can swing the cost of servos or at least closed-loop steppers for the axes and a servo for the spindle, you'll be happier long term. I'm a little negative on DMM, because I was trying to do something unusual; for intended purpose they work great. Night and day difference over the stock motor. Today, I would use larger motors on the axes than I did (~283 oz-in nema23). They work well, but it would be nice to have headroom to crank down the gibs. Also, while extreme, I would consider the replacement of the spindle with a BT30 spindle off eBay, but the tool holding costs go up fast. I'm happy with LinuxCNC and recommend the Mesa 7i76e card, which is very expandable, well thought out, and easy to wire. Just some thoughts that come to mind. Also, while mostly in German, check out CNC Umbau channel. Lots of great ideas in their videos.
ua-cam.com/users/nachtfalke0126
have you been able to pull off the rigid taping yet? I'm guessing it was one of the reasons for upgrading
Hi Rip, sorry to have missed your question. Yes, rigid tapping with two setups. The first method uses a dedicated encoder. I posted a video that some time ago. Then I was using the old motor, but the same hardware works with the servo new. The second method, uses the servo drive's encoder pass-through. I describe problems that I had in a recent Q/A video about the servo. Well, I tried to address some of those problems by switching to a Mesa 7i76E card (I think that's the right model), which has differential I/O and higher sampling rates than the Pico USC I used in this video. The encoder feedback from the drive might be better now, but not perfect. Perfectly fine for rigid tapping at slow speed, maybe up to 500RPM, but gets increasingly off as spindle speed increases. The pass-through is actual a virtual encoder, with a scaling factor applied, but that should not matter. That's OK though, and I go to thread milling before rigid tapping. Best wishes, Kent
This is very much what I am looking to do with my own PM25MV conversion. Can you provide some additional info. What motor/ driver are you using what is your max RPM? Thank you.
They are products from DMM (Dynamic Motor Motion). The motor is 86M-DHT-A6MK1 and the drive is DYN4-H01A2-00. Max rated speed is 5000 RPM (but 5500 RPM also works.) The pulleys are 1:1. Maximum speed allowed by the mill's spindle speed is 6000 RPM.
Great video, what performance in rough milling do you get with this machine? Maybe the spindle is not the weakest part?
Hi Joakim, sorry to respond so late. Thank you for the comment. Where would you look for the weakest spot? Surprisingly, I don't have MRR numbers to share. I did have power monitors on the spindle and stepper motors and I would see the spindle maxing out while the steppers were drawing only a small fraction of their maximums. Perhaps drilling is the close of a comparison that I can offer. With the stock motor, 3/8" into aluminum, without step drilling, was sketchy. When exiting, the feed rate needed to be reduced. With new servo, 3/8" is still probably the maximum without step drilling, but there is no hesitation at exit. A drawback to the 750W servo is that it does peak at 750W, while the stock 750W BLDC would run for short times at a little over 1kW before faulting. Best wishes
@@kentvandervelden facebook.com/SpoonValley-Machines-106524254383808
excuse me.first why did you need to change the normal spindle to be servo motor?what is the benefits gained ,sorry I am not professional so i asked this question but still need to learn from you,thanks
Hi Raif, this is an important question. The servos are expensive and their utility will depend on the application. With the mill, a good reason may be to have a high torque in a small package. While the original BLDC motor should perform better at low speeds, but it's easily stalled below 500RPM. The servo has much more torque at low speeds than the BLDC. The servo supplies constant torque up to rated speed, then it produces constant power beyond rated speed (Power ~= toque X speed.) The max speed of the servo is 2x than the original BLDC. The higher torque is great for drilling and the higher speed is great for small endmills. Both this servo and the original BLDC have the same 750W power rating. Beyond that, the servo has some interesting features that are useful in special cases, including: one can extract current torque measurements (instantaneous measure of load), position accuracy, measure position, etc. Thank you for asking.
@@kentvandervelden Thanks for useful info. I have several AC servos, 1kW 4(12)Nm 2500rpm 80cm frame and 1,8kW 6(18)Nm 3000rpm 110cm frame. My milling machine Optimum BF20 has a 850W BLDC, probably the same as yours.
Is it better to upgrade to the 1,8 kW or the 1kW should suffice, what do you think?
@@jackneill8233 If no trouble, I would use the 1.8kW. With the greater power, you might consider a pulley to step up speed or have plenty of headroom for drills. I picked 750RPM because of its higher speed.
@@kentvandervelden Very good suggestion
Hello, if you could upload the servo connection with the card to control the speed from the software. thanks.
On GitHub, I posted my Python code for controlling and getting status. Let me know if I didn't understand correctly.
github.com/kentavv/dmm-dyn4
@@kentvandervelden Thanks for your attention, but I mean the connection of the board controller to the CN1 connector of the servo driver. thanks
Kent is that the 1.8kw ac servo?
This is the 750W model (medium inertia with brake), which has higher speeds than the higher power servos (5000 vs 3000 RPM.) I finished making the aluminum mounts and the 3d printed mounts survived. The performance, even on 120V, is very interesting and I'm glad I made the change. Top end power is maybe less than the BLDC, but I think the BLDC was being overdriven at the powers > 750W, but the low end torque reliable constant availability and ability to maintain constant speed on the servo is very interesting. Surface finish is best I've had. I'll make a few followups on this about what I find interesting. I've written some software that interfaces to the servo drive to monitor it as well.
In general, in there a huge benefit for using AC servo vs Dc one?
Why did you make this upgrade?
This is an important question, and I'm not yet able to answer. I made the change for a few reasons, including I wanted: 1) a documented and easy to replace motor and drive; 2) a drive which is programmable that I can request stats from during machine operations (github.com/kentavv/dmm-dyn4); 3) built-in encoder for use with rigid taping; 4) a brake for holding the spindle in position (turned out not to be nearly sufficient for holding the spindle during a tool change, but would be useful for broaching; 5) constant-torque then constant-power profile; 6) I had the motor for nearly two years in a drawer; 7) to be different :) Was it worth it??? I'm not convinced yet... I would not recommend quite yet over a VFD AC induction motor. I'm a tinkerer though, and so having something a little different to experiment with is fun. Please see next video or two where I'll compare the two motors. I didn't include that stuff here because it's not fair to compare the BLDC with metal mounts to the AC servo with 3d printed mounts. The lack of rigidity in the 3d printed mounts causes the AC servo to dither and hunt. I'll replace with metal mounts, timing belts and pulleys, and then make the comparisons. Hope this was helpful to you. Again, no recommendation yet. Thank you
@@kentvandervelden
Thanks for the detailed reply.
I hope I will find an answer to my question later.
I will make sure to follow up.
Thanks again.
One gotcha when comparing with torque-speed curves is that power is the product of torque and speed and power is proportional to metal removal rate. Adjusting the gains way up, this AC servo has more torque at the low speeds than the original BLDC, but is stiff. In the end, rated power of both is 750W, so at the optimal speed of each, the same amount of material will be removed by both motors. Greater torque may allow a larger tool to be used, but the metal removal rate remains the same if power is the same. This is all cool but is also all theory. Take with grain of salt :)
Cooool ?It's so hard to find the right engine.
Have you already tested?
How is he doing in steel?
Best regards Stephan
Hi Stephan! I'm sure it'll only be better than the BLDC motor with the exception that one can't over power the servo as long. Not many tests yet, but happy so far.
where did you buy the servo motor from and your cost to do the conversion?
The servo motor came from DMM Tech. Drop me and email and I'll send you a BOM for the conversion. If I remember, about $1500, including $800 for the mechanical kit and excluding the computer. This is on top of the pm25 cost. But most importantly, many many hours of enjoyment and frustrations ;)
Could you show us your dyn4 servo drive settings for comparison .
Absolutely, you can see them at this link. Possibly the only change that I've made since that video was to switch to RS232 input.
ua-cam.com/video/B5TPRmTJN_M/v-deo.html
@@kentvandervelden Thank you Kent i am using a 1.8 Kw Dmm tech motor and DYN 4 drive on lathe spindle and i am working out some issues i seem to be having.
@@ernestrhoades5147 It's a lot of time to commit, but the video I linked as a table of contents to hopefully get you to important parts if there are any for you. Otherwise, let me know if there is something I could help with. I had a lot of trouble, and continue to with respect to the electrical interfaces. In the end, I ditched much of the electronics interface for the serial interface and send commands to set the speed and read position. Not real time, but it'll work. I hope you have better success.
What size motor did you go with?
It's a NEMA34, 86mm, 86M-DHT-A6MK1 is the model number. 750W, which is the largest power DMM Tech with 5000rpm. Power ~ MRR, but higher RPM would help with smaller cutters. We'll see how it all works outs :)
@@kentvandervelden Did you consider using a more powerful, 3000rpm motor and just changing the pulley sizes to keep spindle rpm up?
@@benalexander7388 There's always the speed-torque trade off. Using a pulley ratio to up the RPMs is changing the inertia matching in the opposite direction than what's desired with servos. A large AC induction motor with a pulley system should work well. My electrical is limited as is space on the top of the mill head. I also wanted a motor drive that I could write programs to examine the diagnostics information such as instantaneous torque, current, and position. The servo motor will allow rigid tapping, and is just a little different than what is often done with small CNC mill conversions. I considered a few 1.5+kW spindles on eBay, but DMM was pretty great answering questions. I suspect that I'll come to the conclusion that a step pulley is ideal (high speed spindle and step down the RPMs.) If I'm making a mistake, we'll all learn from it :)
@@kentvandervelden In general, would the issue just be with rigid tapping, since it can't stop/change direction as quickly?
I'd seen discussion about using these DMM servos online but have not seen much implementation or results. I will be following along with interest. The stock motor on the g0704 is very lacking and weight/size of the AC induction motors I've seen puts me off. I was looking at the 750W or 1kW version DMM offerings but I had not considered the effect of the inertia on control.
@@benalexander7388 Sorry, which issue? A larger slower motor step up, it's mainly inertia matching is wrong. However, I calculated the inertia match of this setup. I think it was 5:1 and DMM said one could go up to 20:1, where conventional rule-of-thumb is 10:1. The biggest challenge with rigid tapping is synchronization of z-axes with spindle position. I demoed this in an earlier video with an external encoder and the stock BLDC motor. It works, but the available torque limits taps to small ones at high speed. I picked this motor to write software for it (github.com/kentavv/dmm-dyn4) and to demo something that's a little different. I don't know if it'll work. I used the 3d printed mounts as a quick check of if things look like they might :) Thank you
Nice video, Kent! I’ll be waiting to see how it all turns out. A while back, I put the same motor and drive on a mini mill. It worked great but the motor would behave oddly when reversing direction. Many emails back and forth with DMM did not resolve the issue. I’m hoping you can figure out what I was doing wrong.😂
Here’s a link that shows what I mean.
ua-cam.com/video/_r2KtAtRvEo/v-deo.html
Thank you! How was your servo attached (analog or step-dir speed-dir control) and what mode was the drive configured for (position or speed servo mode?) Did you toggle the servo's enable line at the bottom of the tapping cycle?
I don’t honestly remember how it was configured. It was over a year ago. I followed the wiring diagram they provided and set it up as suggested. I believe the wiring was similar to how you would wire a VFD. It was connected to a Centroid Acorn (excellent product, btw). I still have everything, just currently don’t have a home for it. I bought a Tormach 440 and thought maybe one day I would modify it but it works pretty nicely as is so haven’t changed out the motor.
I am pretty sure there was an enable and reverse. And 0-10v for speed control.
@@ScotY808 I remembered you telling me about this about a year ago. Then I used a high speed camera to check the spindle direction change but in your example it's easy to see with ones eyes. So, when I noticed this on my own machine I thought to contact you but you beat me to it :) I've changed so many things, I'm not sure the combination, but I too saw the reversal problem, and I think the servo was in speed servo mode, using analog input, and the enable line was being used. Maybe toggling the enable at the same time as commanding a starting speed causes the servo to spin an unexpected direction briefly. I can still verify this. I'm working on position servo at the moment and encoder feedback. How were you rigid taping? Did you have the servo drive encoder attached to your controller or a separate encoder? Or, you maybe using the drive in position mode? I'll get all the pieces working and then double check what might have caused this. Regardless, I've seen the problem you saw. Also, DMM said there's a new firmware, so maybe there's some bug in the firmware on the drives we have?
Hi Kent,
I used the motor’s encoder for position feedback for rigid tapping. There’s a connector on the Dyn4 that outputs the signal. I heard about the firmware update and recently emailed DMM again but am waiting for an answer. Michael replied but I didn’t get the answer I needed. Speed servo mode sounds familiar. I am pretty sure that’s what I was using. They told me that the reversing behavior is because it’s a servo and when enabled, it must spin normally, then deal with the reverse command and that’s why you have a brief forward rotation. And they couldn’t get it to behave exactly like a VFD. Or something like that, anyway😂...it’s what my understanding was. So, back then, they were working on some sort of fix for this. The Centroid Acorn was able to deal with this for tapping. You can see it moves down in Z for the split second forward rotation before moving up.