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IndustryArena Forum > MetalWorking Machines > Benchtop Machines > started my cnc conversion for Precision Matthews PM-25MV Mill
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  1. #25

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    Feb 2019
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    Re: started my cnc conversion for Precision Matthews PM-25MV Mill

    Quote Originally Posted by sundewzer View Post


    I didn't buy it for the looks either, if I did would have went the a Grizzly. Just can't beat that forest service green . What I did buy it for was moving the table and head. These thing are really hard to do when bearing are missing balls and bearing are packed with rust not oil.
    https://photos.app.goo.gl/WmP2Xb7j1hoFuVEK6
    This just tells me that they have no quality control in the states. It was hard to turn the handle and the noise was awful. On the flip side all of the mating surfaces look great, that is once I got all the powercoat of them.




    Did you call or contact their customer service? I have a feeling that they would make it right for you.
    I actually contacted them because I had ordered a set of end mills with my machine and couldn't find them. They replied very promptly and told me where they should have been attached to the crate. I simply didn't find them in the first look because I had my son uncrate the machine while I was at work...

  2. #26

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    Feb 2019
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    16

    Re: started my cnc conversion for Precision Matthews PM-25MV Mill

    I didn't check my ballscrew lengths, only tested the ends to make sure they fit the bearings and preload nuts correctly. I'm just starting to machine the conversion parts now.
    If Z or Y are too long, I figure I could cut/grind them down.
    X- I can make my motor standoff a little taller.

    I'm taking a shortcut with the motor standoffs to save a lot of time since I'm doing all the cutting manually.
    I ordered these for the x and y mounts, they are a little tall, so I should just need to cut them down to the proper height. https://www.amazon.com/RATTMMOTOR-St...gateway&sr=8-6

    I ordered a Nema34 mount as well, but its design is different (hollow) and I thought I would have to do significant modifications to get it to work, so I sent it back. Turning the standoffs on a lathe would be a lot easier in this case.

  3. #27

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    May 2019
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    22

    Re: started my cnc conversion for Precision Matthews PM-25MV Mill

    Quote Originally Posted by BrianPM View Post
    Did you call or contact their customer service? I have a feeling that they would make it right for you.
    I actually contacted them because I had ordered a set of end mills with my machine and couldn't find them. They replied very promptly and told me where they should have been attached to the crate. I simply didn't find them in the first look because I had my son uncrate the machine while I was at work...
    I did and they are sending new bearing. Their customer service is great. It is their quality control that is lacking. I understand not catching the bearing that was missing a ball on the Z, it was barely noticeable. The rusted one however was as obvious as a slap in the face with one turn of the handel. But I guess you can't catch everything. For all the other stuff they told me to if I don't want to deal with it spend more money and get the Ultra Precision model. You get what you pay for.

  4. #28

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    May 2019
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    22

    Re: started my cnc conversion for Precision Matthews PM-25MV Mill

    Quote Originally Posted by dazp1976 View Post
    I'll do that for now and see how it goes.
    Motor + bearing carriers weigh in just shy of 4kg on mine (8.5lb ish).
    My slow progress here:
    https://www.cnczone.com/forums/bench...m25-clone.html
    I love the enclosure! That is way more industrial than my plans. All you need now is a chip auger

  5. #29
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    Jan 2012
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    67

    Re: started my cnc conversion for Precision Matthews PM-25MV Mill

    what size of OZ stepper motors should i go on the pm25mv?

  6. #30
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    Mar 2017
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    35

    Re: started my cnc conversion for Precision Matthews PM-25MV Mill

    I was using 400 oz in steppers on X and Y, and a 1200 on the Z (though that was way overkill for the Z).

  7. #31

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    May 2019
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    Re: started my cnc conversion for Precision Matthews PM-25MV Mill

    Quote Originally Posted by rmachinist View Post
    what size of OZ stepper motors should i go on the pm25mv?
    What I did for an estimate on for the 30MV was take my hardest material to cut, SS 304 for me, and guessed at my the toughest cut. I used https://fswizard.com/www/ to get some rough numbers and if you click the blue bar on top you get cutting force. I am not sure if it is radial and axial combined but I assumed worst case it was all radial, came out to about 180#.

    Put that in a lead screw calculator. https://www.amesweb.info/Screws/Lead...meThreads.aspx and got about 800 oz in.

    I knew I wanted Teknic Clearpath SDSK motors so my choice was easy and went with 1100 oz in on all 3 axis knowing that my X and Y are overpowered for 80% of my jobs. I am sure the 640 oz in would have been find but it was $20 more for the bigger motor and I am a sucker for a cheap upgrade.

    I am sure this isn't the best method and I would love to hear what others have done to size their motors.

  8. #32

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    Feb 2019
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    16

    Re: started my cnc conversion for Precision Matthews PM-25MV Mill

    I just went with typical recommendations for the G0704 machines: 570s on the X&Y and a 906 on the Z- I was going to use a 570 on the Z as well, but I wasn't sure if it would be enough as this is my first machine. I don't have anything put together yet, so I can't comment on how well they work.

  9. #33
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    Jan 2005
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    1938

    Re: started my cnc conversion for Precision Matthews PM-25MV Mill

    Quote Originally Posted by sundewzer View Post
    What I did for an estimate on for the 30MV was take my hardest material to cut, SS 304 for me, and guessed at my the toughest cut. I used https://fswizard.com/www/ to get some rough numbers and if you click the blue bar on top you get cutting force. I am not sure if it is radial and axial combined but I assumed worst case it was all radial, came out to about 180#.

    Put that in a lead screw calculator. https://www.amesweb.info/Screws/Lead...meThreads.aspx and got about 800 oz in.

    I knew I wanted Teknic Clearpath SDSK motors so my choice was easy and went with 1100 oz in on all 3 axis knowing that my X and Y are overpowered for 80% of my jobs. I am sure the 640 oz in would have been find but it was $20 more for the bigger motor and I am a sucker for a cheap upgrade.

    I am sure this isn't the best method and I would love to hear what others have done to size their motors.
    That link is for calculating the force produced by an ACME screw. The OP has ballscrews which are much more efficient. Here is a calculator for ballscrews. For efficiency, a ballscrew is about 90% efficient.

    My G0704 has the 570 oz-in steppers on all axes and has proven sufficient in X and Y but I would like a bit more on Z due to drilling forces. The ballscrew calculator says a 570 oz-in motor on a 0.196" (5mm) lead screw at 90% efficiency will give 1027 pounds of linear force. Using your 180 pound cutting force requirement there is a healthy margin. However, for a stepper design, the desired rapid speed may be the driver for motor sizing. This is because stepper torque drops off with increasing RPM and there will be a speed where the stepper will stall. For the 570 oz-in motors I can rapid reliably at about 150 IPM with double spring preload ball nuts. With single ball nuts that speed is closer to 200 IPM

  10. #34
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    Re: started my cnc conversion for Precision Matthews PM-25MV Mill

    Here are the ball screws I just received https://www.youtube.com/watch?v=7UYHzjYW7yg

  11. #35

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    Feb 2019
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    its my understanding that you shim between the ballnuts to create preload when the holes are aligned. The z-axis already comes that way- shimmed in between and attached by the ‘ears’ for this purpose.
    My y-axis came in timed just like yours and my x-axis was pretty close too. I had planned to cut some disks matching the flanges from shim stock.

    The timing on your X-axis looks off by quite a bit, not being sure of the geometry and just spitballing.... but I wonder if the orientation of the 2 ballnuts were reversed, if they would line up closer? The other option might be to turn a spacer to put between them.

  12. #36
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    Re: started my cnc conversion for Precision Matthews PM-25MV Mill

    [QUOTE=rmachinist;2305394]Here are the ball screws I just received /QUOTE]

    The plastic tubes are for removing the nuts without losing any bearings, carefully. put sleeve on end that's not threaded and wind the nut onto it.

    Imo I'd be happy with the Z but not the X,Y. I'd expect them all to look like the Z.

    With the Y, shim between the 2 nuts as needed (I find alu foil good for this, I have some that is 0.01mm thickness) however I haven't had much luck getting mashed together nuts working that well. Having said that it was on my Z which has limited space for making adjustments anyway..

    With the X, what I would consider is removing a nut, putting the mounting block on, replacing the nut so the mount is between the 2, that's if you have threaded holes on both sides of the block. This will aid the shimming process because they are so far out as-is. This way you can skim the block down if you need to to get them close to flush as you can which will then lessen the amount of shimming required. But... doing this may mean you have the annoyance of constantly needing to remove the nut as you make the adjustment. Is the best plan imo though.

    Those grease nipples are a bit of a laugh too. How do you expect to get a grease gun on the Z nut when it's fitted???. You want some elbow fittings and 4mm tubing so you can put the grease nipples on the outside of the machine. Grease then flows from the nipple, through the tube, into the nut.
    Unless you're doing a one shot oil system.

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