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IndustryArena Forum > Metalworking Machines > Benchtop Machines > Precision matthews PM-940M Mill to CNC conversion
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  1. #1
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    Precision matthews PM-940M Mill to CNC conversion

    I am upgrading from my G0704 4th axis CNC to a PM-940M mill, which I plan to CNC over the next couple week/month..

    Here is a quick background. I bought a G0704 mill at the beginning of 2012 and about mid year I finally got the CNC kit installed. At this point I still didn't really know how to create drawings or cut anything.. I spent countless hours over the next 2.5 year getting to where I am now..

    Here is the current G0704 that I am still making parts on:





    I had been thinking about upgrading my machine since projects never seem to slow down. I need a machine that can do more in less time and allow me to have a larger envelope for heavy/larger project.

    I have watched hundreds of YouTube videos and asked the right questions to some of my machinist friends who know what I am after and what will fit my needs. The Precision Matthews PM-940M machine seems to fit my budget and envelope for work. My current G0704 (with the vise mounted) gives me 4.5" x 16.1" of travel. Now I can get slightly more if I remove the vise and 4th axis but with those mounted those are my travels. This new PM-940M allows for 12" x 28" of travel, so this will once again allow for heavy/larger work pieces.

    Here is what the new Mill looks like:





    From the above pictures you can tell I am moving from a 350lbs machine to a 1300lbs machine. I certainly have my work cutout for me.

    The plan is to use the G0704 to cut all my mounting plates. Once the PM-940M is 100% up and running I will clean and tune the G0704 and put it on the market.

    I will be doing short videos of the progress along the way.


    [MEDIA=youtube]RwLKf-eYUqc[/MEDIA]

    I ad a few friends come over yesterday and e go it onto the base, so the real CNC conversion can start now.


  2. #2
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    Re: Precision matthews PM-940M Mill to CNC conversion


  3. #3
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    Re: Precision matthews PM-940M Mill to CNC conversion

    Things have slowed down since I destroyed my grizzly G0704 motor and boards. Not sure what happened. looks like it was just time to replace all the parts.




    I should have the "y" ballscrew installed later today. So the next video should be posted within the next 48 hours.

  4. #4
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    Re: Precision matthews PM-940M Mill to CNC conversion

    Here is the video of the Y axis install and more info on how the brackets were made.

    https://www.youtube.com/watch?v=tF0A2m-ubAI

  5. #5
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    Re: Precision matthews PM-940M Mill to CNC conversion

    Great start....

    Curious why you just didn't rework the stainless y-axis nut you already had made versus making an entirely new one from aluminum? Looked like you only had to re-machine the topside?

    What are your plans to retain the y-axis bearing from popping out? Fasteners around the periphery or perhaps another plate?

    -Mike

  6. #6
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    Quote Originally Posted by MikeSherman View Post
    Great start....

    Curious why you just didn't rework the stainless y-axis nut you already had made versus making an entirely new one from aluminum? Looked like you only had to re-machine the topside?

    What are your plans to retain the y-axis bearing from popping out? Fasteners around the periphery or perhaps another plate?

    -Mike
    It was easier to remake the new bracket because it was aluminum and also because 2 of the top screw holes were off just enought that the heads of the screws wouldn't allow them to set down in the recessed holes in the ballnut flange.

    I won't need to secure the bearing down because the bearing is pinched between the jam nut and the shoulder of the ballscrew. This means the shaft would need to move out of the bracket with the bearing. Once I install the lovejoy couplers to the shaft and mount the motor, the shaft can't move towards the motor because it will be solid/tight and it can't move towards the rear because of the bracket where the bearing is located.

    However the issue I may have is if the ball nut hits the bottom part of the frame it will then force all the pressure on itself or the bracket in the front. This could cause a problem, so I might make a stopping plate and mount it on the chassis so that the plate will cause the motor to fail not binding everything up because it has compressed the ballnut and bracket into each other.

  7. #7
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    Re: Precision matthews PM-940M Mill to CNC conversion

    If you grab the ballscrew from the front where you would connect your lovejoy coupling....what stopping the entire bearing from pulling out of its bore?

    You do not want your stepper motor taking any thrust loads.

    Perhaps I'm missing something?

    -Mike

  8. #8
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    Quote Originally Posted by MikeSherman View Post
    If you grab the ballscrew from the front where you would connect your lovejoy coupling....what stopping the entire bearing from pulling out of its bore?

    You do not want your stepper motor taking any thrust loads.

    Perhaps I'm missing something?

    -Mike
    That is how my cncfusion kit is designed on my g0704. It wouldn't be hard to put on the front bracket and hold the bearing in since the bearing sticks out .015 from the pocket.

    I just didn't realize it was a huge deal.

    Thanks for the heads up.

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    Re: Precision matthews PM-940M Mill to CNC conversion

    **update**

    For the very few people actually reading this thread, I should have a new video posted in a few days, I am working out a few issues with travel on my "x" axis. Looks like a few more modifications should yield 3-4 more inches of travel.

  10. #10
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    Re: Precision matthews PM-940M Mill to CNC conversion

    Quote Originally Posted by unknownpro View Post
    **update**

    For the very few people actually reading this thread, I should have a new video posted in a few days, I am working out a few issues with travel on my "x" axis. Looks like a few more modifications should yield 3-4 more inches of travel.
    I am following and reading, I think its interesting to follow one of the bigger conversions. There have been a million of the smaller conversions, but not many of the bigger. Nice work on the vids.

  11. #11
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    Re: Precision matthews PM-940M Mill to CNC conversion

    I moved the ballnut that is located under the table to the right and this has given me just over 1" of extra travel on the left side.. i describe in the video changes that need to be made to the right side of the bearing mount that will give me another 2-3/4 inches.

    https://www.youtube.com/watch?v=Bx_pHfLBn3s

  12. #12
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    Re: Precision matthews PM-940M Mill to CNC conversion

    Wait a minute.. Maybe I missed this in your video, but is the driven end of that ballscrew unsupported??? It looks as if you've got the end just connected to the stepper via a coupler. Any sort of load will separate the these couplers, basically making the machine unusable. I've seen this design on really small engraving machines, but it definitely will not work with any sort of load (even the weight of the table is a lot in this case).

    I would highly recommend revising your design.. Like preloaded angular contact bearings in a housing to support thrust loads on the driven side and a floating bearing on the free side.

    Again, please forgive me if I've missed something. Cheers, Devin

  13. #13
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    Quote Originally Posted by crazydiamond View Post
    Wait a minute.. Maybe I missed this in your video, but is the driven end of that ballscrew unsupported??? It looks as if you've got the end just connected to the stepper via a coupler. Any sort of load will separate the these couplers, basically making the machine unusable. I've seen this design on really small engraving machines, but it definitely will not work with any sort of load (even the weight of the table is a lot in this case).

    I would highly recommend revising your design.. Like preloaded angular contact bearings in a housing to support thrust loads on the driven side and a floating bearing on the free side.

    Again, please forgive me if I've missed something. Cheers, Devin
    This is exactly how my grizzly is designed. I cut stainless and titanium all the tube with no issues.

    The coupler can't come apart because the shaft has a locking cap on the bearing side. You can't just simply pull the table off on the left side because the locking cap is compressing everything. This locking cap can be seen in the video.

    Now I do understand what you mean about having a bearing mount on the motor side but I have yet to see any Cnc kits that do this, not saying they don't exist, I just haven't seen any.

  14. #14
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    Re: Precision matthews PM-940M Mill to CNC conversion

    Quote Originally Posted by unknownpro View Post
    This is exactly how my grizzly is designed. I cut stainless and titanium all the tube with no issues.

    The coupler can't come apart because the shaft has a locking cap on the bearing side. You can't just simply pull the table off on the left side because the locking cap is compressing everything. This locking cap can be seen in the video.

    Now I do understand what you mean about having a bearing mount on the motor side but I have yet to see any Cnc kits that do this, not saying they don't exist, I just haven't seen any.

    Are you using a double row AC bearing? If so, I don't see why it wouldn't work, but with a single row, I don't see how the bearing won't get pulled apart by force.

  15. #15
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    Re: Precision matthews PM-940M Mill to CNC conversion

    video is loading


  16. #16
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    Re: Precision matthews PM-940M Mill to CNC conversion


  17. #17
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    Re: Precision matthews PM-940M Mill to CNC conversion

    Cool vid. Looking forward to seeing the machine in action, would be great to see a walk through of the whole machine. Looks like a beast!

  18. #18
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    Re: Precision matthews PM-940M Mill to CNC conversion

    Any updates?

  19. #19
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    Re: Precision matthews PM-940M Mill to CNC conversion

    What did that big guy end up costing you landed?

  20. #20
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    Re: Precision matthews PM-940M Mill to CNC conversion

    The machine is done for now. Several things still need to be changed or updated. Everything is working with the exception of the 4th axis. I have put around 500 hours of cnc cutting on this machine since it has been converted over to CNC.

    If you were wondering why I haven't posted for some time, it's because I was tired of people trying to tell me it's wrong or should be done a different way(received a lot of private messages not all from here) I am a hobbiest and not some CNC guru. I do this for fun and this was probably the single largest project I have done on my own with no help and with no references online.

    Yes, maybe it's wrong or not correct in your eyes but it's not your machine and you don't need to worry about it. I stopped posting stuff here because, I don't want to hear the "your wrong" comments. I have plenty of stuff posted on YouTube.

    I purchase a fiber engraver and it takes up most of my time now. I would post some information on rotary axis circumference engravings and how to setup the laser engraver but don't need the negativity that comes along with it.

    Peace brothers.

    - unknownpro

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