PM940CNC Upgrade Build

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    Default PM940CNC Upgrade Build

    Hey everyone, long time lurker (been reading info on here since sometime in 2013) finally contributing a little bit. I'm an engineer who's worked in a few different industries, currently working as an optomechanical engineer designing fiber lasers. I'm a tinkerer and am interested in nearly any type of manufacturing, but most of what I do at home is welding and machining.

    I've got a Precision Matthews PM940CNC, which I originally bought to make some custom watches. I got one of Matt's first batch in 2015 -- I'm not sure if he's even selling a CNC line anymore based on his site. It has now been completely disassembled twice, first to move into a basement, then to move into the garage of my new house, seen here:




    I paid $7,200 for it, so I think there's some good value in it (pricing is basically identical to Tormach 770, and less than the 1100). It has a cutting volume of 3.5 cubic feet (X-23" ,Y-14", Z-19"), which is a little bit more than twice the PCNC1100's, although a lot of that is in Z and is often not useful. It has a 1.5HP geared spindle motor and is setup to run at 3,000 RPM max from the factory. The axes motors are steppers, running double nut ballscrews. The machine itself weighs about 900 pounds (not including the control box or the stand).

    Basically the only 'upgrade' these things comes with is an auto-oiler (which doesn't do the Z-axis ways, for that matter). I've been designing upgrades for it for a long time now, and have really just gotten into the meat of them. So far, I've completed adding an enclosure to it:



    I'm currently working on installing a hydraulically actuated power drawbar and a belt drive motor suitable for higher RPM. Both projects are largely done and just waiting for installation, I'll add some pictures as I progress.

    Feel free to pop any questions you may have my way.

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    Default Re: PM940CNC Upgrade Build


    I figured I'd update this with some of my CAD drawings since I'm still finishing up my spindle motor upgrade. This is kind of a road map of what I want to add to my machine, in addition to being actual CAD parts/drawings that I've completed (just waiting on fabrication, testing and improvement). I do most of my work in Solidworks and the rest in Fusion 360, which is also what I use for all my CAM.

    1. Upgraded spindle motor with belt drive.
    2. Hydraulic power drawbar.
    3. 18-tool automatic tool changer (which I'll talk about in another post in the future).
    4. 36" x 12" steel fixture plate.

    Most of my CAD parts I try to keep pretty basic. For purchased parts where the vendor doesn't have a CAD model, I generally I just model mounting dimensions and the outline of the part. For example, the Baldor motor in the picture above is basically just a truncated cylinder and feet. I didn't worry about modeling cooling vanes, the fan, etc.
    For parts that I have to make, I'll flesh them out complete and usually generate a drawing to work from in the shop.

    The spindle upgrade is pretty simple in theory. It's just a base to support the new motor and two pulleys, as well as a 10 rib J-belt.
    In reality, those pulleys are fairly hard to make. The spindle pulley has to match the spindle splines, which are not a standard broach size. The motor pulley is large, so it was difficult to turn on my tiny lathe (mostly due to limited horsepower), but otherwise fairly straightforward as it just had to fit onto a 1.125" shaft with a 1/4" keyway.
    In addition, I had originally designed this so that motor position can be shifted using a pair of screws, so the sides are actually rails. This make installation much, much harder. I have already designed a potential replacement that would not use rails, I'm hoping I can get this installed by switching out the bolts and being creative with my assembly steps, but we'll see. I'll do in an in-depth post on it once I've gotten further along.

    This hydraulic power drawbar is very simple. It only requires three parts to be fabricated (although the four tubes do need to be quickly faced and turned to length on a lathe as well). Those three parts are very simple: a plate with six holes and a channel, and a plate with five holes (the center hole does require a single point threading operation, but still not very difficult). It's also pretty cheap -- not shown is the most expensive part, which is the hydraulic intensifier. It uses compressed air to pressurize the hydraulic fluid, and allows for a much more compact assembly with higher output force than even a multi-stage air cylinder would provide. I have everything for this ready to go except the spacer used to hold the Bellevilles in place, which I will get to after I've completed the motor upgrade.

    Skipping over talking about the ATC for now, I'd also like to add a fixture plate. I generally use a dual position vise at the moment, but long term my projects will mostly be fixtured, and the convenience that a fixture plate gives in terms of change-overs is great. I'm hoping this will be a quick and fun project sometime this spring.



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    Default Re: PM940CNC Upgrade Build

    I would take a look a the Grizz G0704 build thread on their hydraulic draw bar set up. They had to modify their draw bar mount because it was not simply strong enough to handle the force of the hydraulic piston. As casual observer, I think you would experience significant flexing on the mount and over stress the threads on the 2 shoulder screws connected to the head. Whatever you decide, keep the updates coming!!



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    Default Re: PM940CNC Upgrade Build

    First time I've seen "The Grizz" thread, thanks for the heads up. I guess I haven't been on here much in the last year or so. Great project, almost unbelievable finish, but really indicative of why I've gone a different path. They're making lots of one-off parts in an unoptimized design. I've approached all of my modifications the same way I would a product in my day job, so I've bought most parts off the shelf, and what's not available I've made myself and documented. It's a lot faster and cheaper that way -- especially for anyone who wants to follow along after.

    I am not shooting for nearly as high drawbar pressure as The Grizz duo (although my system is pretty similar to theirs, albeit with a lot more off the shelf parts). First and foremost, I don't think there's any reason to run much higher than that for TTS tooling. The tools are just not big enough -- the numbers I'm looking at put me into 40 taper drawbar force ranges, and the numbers the Grizz is running are in the 50 taper range! Like I said before, to me this is an optimization project, and they seem to err on the side of overbuilding.

    I've run simulations on my design and expect it won't have any issues. Like Nick noticed, there is about 1 thousandth deflection on the open ended side of the plate, but obviously the stress isn't so high the part immediately breaks. So the concern then is cyclic loading, and based on the max stresses my analysis is spitting out this will run millions, maybe tens of millions of cycles.

    That said, proof is in working hardware! I'm hoping to have the drawbar functional by the end of the month, I'm currently a little sidetracked rebuilding a Quincy 325.



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    Default Re: PM940CNC Upgrade Build

    The first order of business is to uninstall the old motor. That's pretty simple: unscrew the wires in the junction box, pull the four bolts that hold it to the head, and lift it off. At 50 pounds, it's heavy but not too difficult (note I'm 6'2" and 230# -- possible bias).

    While I've got the chance, I'm going to pull the gears from the stock drivetrain out of the head. This will remove a little weight (any more weight I can remove is a good thing -- the new motor is 100 pounds), but most importantly it will prevent the gears from engaging by accident. It's also a good opportunity to drain the oil from the head.

    Gears and gearbox cover pulled off the mill. The shaft closest to the top is the motor driveshaft, the second on is an intermediary that transfers power to the high/low gear shaft, which is the one laying down. The final shaft is more of a collar that fits onto the spindle.


    Here's the inside of that shaft. It looks like this part was made by pressing a few separately made parts together, although I'm not 100% sure on that. It's certainly a complex part, with the internally broached keyways for the spindle spline and two sets of gear teeth.

    This could probably be removed at this point, but I left it in since it liked helps to stabilize the spindle. This will be particularly important once the belt drive setup is applying force all the way at the top end of the spindle.


    Here's the top of the spindle. That cover (covered in oil, with the three screws, around the spindle) is the oil seal, which I've left in for now. I've drained most of the oil out at this point (into the pan below the head, somewhat visible).





  6. #6

    Default Re: PM940CNC Upgrade Build

    I've been following your build with a close eye, as I have just purchased two PM-940's which I'm looking to convert to CNC as well.

    Do you have any updates on your build?

    Any insight into your ATC?

    I sent you a PM as well.



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    Default Re: PM940CNC Upgrade Build

    I've been messaged AutomatedIngen a bit, figured I'd update the rest of y'all on the current state of the upgrades: the VFD I have is throwing a low DC bus voltage fault, and I believe it's bad. I've ordered a new VFD and a new motor, mostly because there aren't any good options (from a price standpoint) for a 5 HP single phase VFD. The other thing that's been distracting me is completing a compressor rebuild (you can check it out on my blog -- https://andrewbaranwagner.com/), and getting some new Shars vises (also on the blog, even includes "measurements").

    In addition, the plans for the enclosure I built as well as CAD models for the PM-940 are available on my website, https://www.wcubed.co/. Note that the "Home" button in the menu bar isn't working correctly but otherwise the site is fully functional.



  8. #8

    Default Re: PM940CNC Upgrade Build

    Cool project. I'll be following along.

    I have three Shars vises, one 6" and two 4". The two 4" vises are on my mill at almost all times, I love them. The 6" is fantastic too, I only need it occasionally though.

    Last edited by CL_MotoTech; 04-04-2018 at 06:39 PM.


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    Default Re: PM940CNC Upgrade Build


    The new spindle motor and pulleys are finally installed and working (and all the gearing and oil is out of the head).
    As you can see in the picture below, I ended up with two cap screws to hold the spindle pulley in place. This is because I did a poor job on the bore and the pulley had 0.020" runout. I just added the second cap screw and got it to within 0.002", which really reduced the noise level.
    The next step is to run the spindle up in steps and see how the temps look. It's currently running the stock bearings, but I do have replacement angular contact bearings that are good up to at least 8k RPM with grease.
    After that I want to try out some commercially available pulleys as I put together the BOM and instructions for the plans I'll be selling.

    The biggest benefit by far is the difference in noise level. It now makes 77 dB at 3k RPM, compared to 85 dB with the gears in place.



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    Default Re: PM940CNC Upgrade Build

    Also tested and installed the VFD.



    The new VFD all wired up, except for the brake resistor.


    I finally got around to testing the upgrade VFD, only to discover that it’s throwing a ‘low DC bus voltage’ error, which probably means something inside is not working right. I couldn’t get it working again and a replacement is $1k (I paid much less for mine on Ebay, but there don’t seem to be any floating around there now). I confirmed the motor worked with my Huanyang VFD, but I don’t trust one of those enough to make it permanent. Also, the cast iron motor I have is crazy heavy (100 lbs), so both for ease of installation and Z-axis acceleration a lighter motor is a plus.

    I went out and bought a used Baldor EM3610T (3 HP, two pole, 240V, steel banded case) on Ebay, and had to wait a few days to find out which face mounting kit was correct (according to Baldor, the 35-1325GLD, the 35-1325 will work too but the color doesn’t match). Finding C-face kits can be a pain and I strongly suggest you buy a motor which is sold with it already installed, like the CEM3610T.
    I also bought an LS (formerly LG) VFD from Wolf Automation. There are a lot of good options for cheap single-phase drives in this horsepower range, including Fuji and Delta.




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    Default Re: PM940CNC Upgrade Build

    Sorry about the poor formatting, you can also read this at https://andrewbaranwagner.com/2018/0...pgrade-part-4/ where the formatting works.

    Time to switch the tapered roller bearings (TRB) out for angular contact bearings. The primary benefit is that AC bearings allow higher speeds, particularly when running only with grease. First step was to pull off the seal above the top spindle bearing, remove the nut and pull the spindle out.








    I dunno what kinda grease was in here, but there’s certainly a lot of dirt, probably largely as a result of having too much grease. This machine has probably only run for a couple hundred hours, so realistically the grease pack it had now should have lasted a while, and you can see in the first picture that the rollers look pretty clear (the grease forms a thin film on the rotating elements of the bearing).
    I didn’t take any pictures apparently, but to get the quill out of the machine, you need to remove the quill retaining bolt (on the left side of the head), then loosen the quill lock. If you have the quill arm that may need to be removed, but as I have already removed mine I’m not sure. I have also already removed the quill DRO and the clamp that holes it
    The next step is to knock the TRB cones out of the quill.











    I cleaned up the quill face a bit after this, but you can see how much grease was jammed into the rollers and cages when I removed them, and how dirty the inner bore is. Most of the inner bore was hard enough it didn’t come off by wiping, and that stuff I left in there. Whether that was a good choice remains to be seen.
    Time to press in the new AC bearings. Note: it would have been a better plan to grease them before doing this.






    And back into the machine.








    Now, I put way more grease than necessary because I forgot to grease them before, and my hope was that some excess would move under gravity in the top bearing, and that I would force some through by hand in the bottom bearing. I also wiped away a lot of the grease after running the spindle at 500 RPM for a little while to warm things up and spread the grease onto the balls. You’re only supposed to fill about 1/3 of the open space in the bearing (according to SKF, who should know), however ultimately the grease will convert to a thin film and coat the bearing, and any real excess will be forced out, particularly at high RPM. Excess grease will hold onto dirt and potentially migrate back into the bearing which isn’t great. If the space confines the grease in the bearing it will also cause excess heating, even if it’s clean.







    Here’s what they look like after a few hours of running. I ran the spindle up to 7k in 500 RPM increments over the course of 5-6 hours (I was working on other stuff around the shop, the only rule I had was that I waited at least 10 minutes to measure temperature, and if I had already measured noise then I confirmed the measurement).

    The noise produced with the AC bearings is lower than the TRBs, although the modified motor and spindle pulley mounting may be a factor in that. Both are way better than the geared setup, which ran at 85 dB at 3k RPM.
    One interesting thing to note was the peak around 6k RPM — some sort of resonance frequency perhaps. I remeasured that point going up and down several times to confirm, but it really does get quieter if regardless of whether the RPM is reduced or increased from there.

    Both bearings are in a good temperature range for the application, and there’s certainly head room to run the spindle faster. I’ve gotta scratch my head some more about why the smaller bearing is hotter.
    Time to pop the seals back on and try out ripping some aluminum.



  12. #12

    Default Re: PM940CNC Upgrade Build

    Nice tutorial. How did you find changing the bearings? I have changed spindle bearings for my G0704 and have yet to do it for my PM-940's. Did the change require any special tools, did you require any spacers?

    Still keeping a close eye on your build.



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    Default Re: PM940CNC Upgrade Build

    Changing the bearings was a breeze, probably less than an hour all told for it. I spent more time figuring out that the lower dust cover is threaded than I did pulling out the rest of the assembly and replacing the bearings.

    No specialized tools required, unless you count a pin wrench. I did not have to use any spacers, which surprised me, although I can't remember if there's a difference in height between the TRBs and ACBs off the top of my head.



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    Default Re: PM940CNC Upgrade Build

    Its possible that with the ACB's the smaller bearing is heating more as its taking the same load as the larger ACB when just running (i.e. your preload).
    When a real load like drilling occurs it will unload the top bearing just slightly as it loads the lower bearing, putting more of the heat into the lower one.



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    Default Re: PM940CNC Upgrade Build

    It might be worth noting that the bottom bearing race can be removed by driving it out with the two holes that are drilled in the quill. They are often filled with crud and you can't see them.

    Also as far as vibration. I have done 4 of the clone spindles so far and some are much better than others. Some had lots of vibration at 4K and were not good for any higher speeds and others were quiet and smooth but still not perfect. You really need to pay attention because at 8K if you have real vibrations it may cause a failure.

    Having a pulley fly across a room at 8K is not really something I would like to see.

    youtube videos of the G0704 under the name arizonavideo99


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    Default Re: PM940CNC Upgrade Build

    Quote Originally Posted by ninefinger View Post
    Its possible that with the ACB's the smaller bearing is heating more as its taking the same load as the larger ACB when just running (i.e. your preload).
    When a real load like drilling occurs it will unload the top bearing just slightly as it loads the lower bearing, putting more of the heat into the lower one.
    That is a good point for drilling -- but given that most of the time I'm using an end mill, I guess that temperature may actually go up. It shouldn't be a problem to do some checking on the top bearing with the machine cutting, I'll have to verify.

    Quote Originally Posted by arizonavideo View Post
    It might be worth noting that the bottom bearing race can be removed by driving it out with the two holes that are drilled in the quill. They are often filled with crud and you can't see them.
    Are these underneath the seal that goes around the top of the lower bearing housing? I don't remember seeing anything, but I didn't pull off that seal.

    Also as far as vibration. I have done 4 of the clone spindles so far and some are much better than others. Some had lots of vibration at 4K and were not good for any higher speeds and others were quiet and smooth but still not perfect. You really need to pay attention because at 8K if you have real vibrations it may cause a failure.

    Having a pulley fly across a room at 8K is not really something I would like to see.
    I somehow tripped the breaker for the control computer (which is concerning for different reasons) and when Mach3 started up with the wrong settings it managed to run the spindle up to 10k -- so now I know the pulleys aren't the first things that fail as the belt actually came off. I assume that's due to a lack of balancing causing axial misalignment between the motor and spindle shafts, but it certainly was concerning at the time.

    I will probably try to take it up to 8-8.5k in a more controller manner later today.



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    Default Re: PM940CNC Upgrade Build

    I’m trying to wrap up the documentation for the spindle belt upgrade so I can get it up on wcubed.co, and since spring has sprung I’m also pretty busy getting the yard in order. I did find some time to work on adding flood coolant and tying in the air blast delivery to it.










    I’m using a Brute 20 gallon tank with some prospecting sifting screens, and the original 4 GPM coolant pump mounted on a polycarbonate stand to keep it above the coolant level. The manifold is from Automation Direct, and the hoses are standard Loc-Line (one 3/8? NPT that came with the mill, the rest are 1/4? NPT). The system is waiting on me to make a drain from the stand into the filters on the coolant tank.
    I also have a new drag chain waiting to be installed, which is large enough to carry the coolant line. The Z-axis end stop sensor wire needs to be run down that, as well as the motor cable and the lines mist coolant and air blast, so it should help tidy things up a bit.
    Bonus picture: when you have to tap some M3 holes but don’t have a tap holder small enough, a TTS ER20 holder can come in handy.




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    Default Re: PM940CNC Upgrade Build

    Anybody want any of the parts out of the head before I chuck them? I also have all the quill lever components. Yours for the cost of shipping, shoot me a PM here or an email through my site.



    Total was 32 pounds, in addition to the ~20 pounds that came off with the quill lever. I think most of the weight in this box was the cast iron top of the head (which I'll note has been cut in half as I was going to use the forward section as a mount for the hydraulic drawbar, but have decided to use aluminum instead).



  19. #19

    Default Re: PM940CNC Upgrade Build

    Nice updates.

    Wow 32 pounds removed from the head casting plus the quill lever, that's quite a bit of weight removed.

    I envisioned filling the casting of the head with epoxy granite, and being I am going to counterweight my Z head it odd to be fine. I wonder though if doing that will help keep vibrations down and increase stability or will it equate to a waste of added weight.

    Your moving closer and closer to your ATC building, can't wait to see that.



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    Default Re: PM940CNC Upgrade Build

    Sorry for the radio silence everyone. I expect to have an update on the hydraulic power drawbar in about a week, just ordering the final parts for it now. Once that's working it'll be time to get to work on the ATC.

    The plans for the spindle belt drive upgrade are now available on my site (https://www.wcubed.co/product/rf45-b...version-plans/), as are the machined parts for it.



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