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  1. #1
    Join Date
    Mar 2009
    Posts
    27

    PM25 stalling X and Y

    Greetings,

    I'm still pretty new to milling machines, so keep that in mind. I purchased a PM25MV, and converted it to CNC using one of the common conversion kits. The kit uses NEMA 23 (570 oz-in) motors for X and Y, and a 34 (1200 oz-in) for the Z. The Z works great, no problems at all. Y works fine as long as X is nearly centered.

    The problems start when the X table travel is more than maybe 6" to the left or right, and less if there's extra weight on the table. It seems that when the weight of the table gets offset to one side or the other, it causes extra friction, and the NEMA 23 motors stall. Just a finger tip lifting on the heavy end is enough to make it work.

    Mechanically, I don't see any significant issues. I've had it apart, and it seems smooth. It's well lubricated with Vactra #2. I've read other posts that suggest this is somewhat normal for these type machines, and I suspect that's true.

    My question is why don't we just use stronger motors? Why not NEMA 34's on all axis to reduce the issues? Does anyone make adapters for the NEMA 34 motors?

    Thanks,
    Rusty

  2. #2

    Re: PM25 stalling X and Y

    Make sure you have the ball screws mounts in line with your ball nut. If there is binding you can get step loss. If this is fine, then it's a way issue. On my G0704 if I put two 4" vises and a 6" 3 jaw chuck on the extended end at full X+ or X- it will stall the steppers at anything above 140ipm. If I take one of those items off it will run at full rapid without stall, with less load I can up the max rapid. In my experience, you will have to run the ways a little looser than you might like to get everything to run really consistently. If you run the table around by hand, no screws, you should be able to move both axis without a lot of effort, but the important thing is to identify tight spots and try to get those worked out.

    Also, I don't think bigger motors are needed when you get it all adjusted properly, so people don't use bigger motors.

  3. #3
    Join Date
    Mar 2009
    Posts
    27

    Re: PM25 stalling X and Y

    Thanks for the comments. I spent a couple weeks fighting this issue, and I finally just set limits for X short enough that I could trust it. I'm certain the screw isn't binding, and no adjustment of the way seems to correct the issue.

    I tried everything I can think of for motor settings, and they should be as strong as I can make them. One thing I didn't consider before was whether my 570 oz-in motors are really as strong as they're supposed to be. Can you reliably measure this? I'm thinking maybe a torque wrench turning the motor when it's trying to hold position?

    Thanks,
    Rusty

  4. #4
    Join Date
    Mar 2003
    Posts
    35538

    Re: PM25 stalling X and Y

    They only have 570oz of torque when they aren't spinning. Once you get to 400-500rpm, they lose about 2/3 of their torque.
    Gerry

    UCCNC 2017 Screenset
    http://www.thecncwoodworker.com/2017.html

    Mach3 2010 Screenset
    http://www.thecncwoodworker.com/2010.html

    JointCAM - CNC Dovetails & Box Joints
    http://www.g-forcecnc.com/jointcam.html

    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)

  5. #5
    Join Date
    Mar 2009
    Posts
    27

    Re: PM25 stalling X and Y

    Yes, thanks. I was aware of that. I might try measuring one when it's holding still. It's a pretty far fetched theory, but I'm out of better ones.

    Rusty

  6. #6

    Re: PM25 stalling X and Y

    They motors should be fine. I don't think I'm even using 570's I think I went with 350oz steppers, I cant remember though. At what feed are they stalling? The only time I really struggle is when I get up into the 200ipm feed rates. I can run one vise with a part in the middle of the table a 180ipm rapids all day without issue. It's when I start adding more vises that I get into trouble.

    What controller software/hardware are you using?

  7. #7
    Join Date
    Mar 2009
    Posts
    27

    Re: PM25 stalling X and Y

    If I try to drive to the ends of the table, it will stall at any speed. I keep it at 50 ipm max, and it will stall way before getting to the end of the table travel. This is with no extra weight on the table. I have noticed that it runs much better one direction than the other when it gets near the end.

    This is the hardware I bought- https://www.automationtechnologiesin...or-3-axis-kit/

    Software is UCCNC with one of the Ethernet controllers.

    Thanks,
    Rusty

  8. #8

    Re: PM25 stalling X and Y

    I found I had to turn my accelerations way down in UCCNC relative to Mach 3. I think perhaps it has to do with UCCNC actually accelerating at the numbers you input whereas Mach doesn't, but I don't know? So maybe try that.

    You might also want to check your step pulse and dir pulse settings. I know with UC300eth and Mach 3 I had to set step pulse to 5 and Dir pulse to 10 for my drivers or they really missed a lot of steps, similar to what you are seeing. I'm using a MX3660 and a G540 in my machine.

  9. #9
    Join Date
    Mar 2009
    Posts
    27

    Re: PM25 stalling X and Y

    Acceleration is pretty low now, and even low single digit numbers didn't help as I recall. I'm not sure what you're referring to step pulse and direction pulse numbers. I don't see a setting like that. I'll attempt to attach captures of the general settings and X-axis.

    Thanks,
    Rusty

    Attachment 409486
    Click image for larger version. 

Name:	x-axis.jpg 
Views:	0 
Size:	97.5 KB 
ID:	409488

  10. #10
    Join Date
    Jan 2018
    Posts
    1516

    Re: PM25 stalling X and Y

    Reconfigure drivers and system with lower steps per unit and try that. I reckon your microstepping is too high myself giving ridiculous resolution and losing more torque.

    I work in mm and when I started out I used a high microstepping of 10,000 on the drivers and 2500 steps per unit for a 4mm screw pitch. That gave me a resolution of 0.002mm and it stalled like crap even at 80rpm (320mm/min rapids)
    Now I use it with drivers set at 1600 and steps per unit at 400. This gives a resolution of 0.025mm (big difference in settings) and my torque/reliability increased.
    I can now rapid at 1500mm/min and if I change it to a res of 0.05mm it will go quicker.
    To be honest you only need a resolution of 0.05mm on a mill tbf.

    Many off the shelf hobby mills only have a res of 0.01mm which is hardly any microstepping at all like 1/2 stepping.

    All this was with the same elecs. My machine is a bit smaller but I am converting a PM25 clone atm.

    My 425oz/in 23 motors will be going on my 25's x&y for now using low step settings until I can afford some 1100oz/in 34's. My Z is getting a 1600oz/in immediately.

  11. #11
    Join Date
    Mar 2009
    Posts
    27

    Re: PM25 stalling X and Y

    Thanks for the comments. During my weeks of initially trying to make this work, I tried lots of different microstepping resolutions on the controllers, with the corresponding steps per unit. What I posted is back to the defaults, since it never really did any better than this. The default for the controller gives 1600 steps/rev, and my unit is an inch. The settings I have now give .0012" resolution, which equals 0.03mm, so it's not so different from what you're using.

    I can accept that my machine might have more friction than ideal, but I haven't found anything I can realistically do about it. I may consider moving up to stronger motors just to see how much that helps.

    Rusty

  12. #12
    Join Date
    Jan 2018
    Posts
    1516

    Re: PM25 stalling X and Y

    Quote Originally Posted by 13brv3 View Post
    Thanks for the comments. During my weeks of initially trying to make this work, I tried lots of different microstepping resolutions on the controllers, with the corresponding steps per unit. What I posted is back to the defaults, since it never really did any better than this. The default for the controller gives 1600 steps/rev, and my unit is an inch. The settings I have now give .0012" resolution, which equals 0.03mm, so it's not so different from what you're using.

    I can accept that my machine might have more friction than ideal, but I haven't found anything I can realistically do about it. I may consider moving up to stronger motors just to see how much that helps.

    Rusty
    Hmm. Fair enough. God help me with mine then using the 425's.
    Looks like we're probably both forking out for some 34's.

    Either one of these will do me.
    https://www.ebay.co.uk/itm/German-Sh...r/192215700849
    https://www.ebay.co.uk/itm/EU-Free-s...l/262956803872

    https://www.ebay.co.uk/itm/Mount-a-N...0/283115937147
    23 to 34 adaptor with measurements listed if that's of any use to you.

  13. #13
    Join Date
    Mar 2009
    Posts
    27

    Re: PM25 stalling X and Y

    Thanks for the 23-34 adapter link. That was on my list of things to search for tomorrow.
    Rusty

  14. #14
    Join Date
    Jan 2005
    Posts
    1943

    Re: PM25 stalling X and Y

    I'm not familiar with the program you are using, but I see you have a kernel frequency of 100kHz selected. At 8137 steps/in, that is 787 IPM. I hardly think your running that fast. I know that on Mach, it is suggested to set kernel frequency as low as possible to avoid problems. A dirty step pulse signal will cause a stall as fast as anything as it is seen as an instantaneous acceleration. I'd first lower kernel frequency to 25kHz which will still give you capability for 184 IPM in terms of step generation.

    As far as the 570 oz-in motors go, I have them on all 3 axes of my G0704 and they work fine at 8000 steps/in, 20 in/sec^2 accel, and max rate of 140 IPM. I don't have missed step problems unless I push the machine too hard, but that is pretty hard. I'm using KL-6050 drivers at 48V, and LinuxCNC through parallel port on an ancient P4 desktop.

  15. #15
    Join Date
    Mar 2009
    Posts
    27

    Re: PM25 stalling X and Y

    A lower kernel freq is something I haven't tried, and it will be simple to test. This is an Ethernet interface that's supposed to be good for 400 kHz, so 100 kHz should be pretty conservative. The Ethernet does go through a switch, and I can try running it direct, but I really don't suspect this to be a problem because the machine can run plenty fast near the center. The problems only start when the table weight if off balance.

    Thanks,
    Rusty

  16. #16
    Join Date
    Aug 2005
    Posts
    1091

    Re: PM25 stalling X and Y

    Hi,
    570oz.in motors are more than adequate for your machine’s X & Y axes.
    They should be provided with around 5A/phase
    I couldn’t see how much current you are feeding them. Are you providing them with their rated current?

    I run my TM20VL machine which is the same size as yours with 570oz.in motor on the X & Y axes controlling then from a Gecko G540 that only drives them at 3.5A/phase.
    https://youtu.be/caZ6F5MT8FA
    https://youtu.be/AjfhQUBjBjI

    As you can see from the 2nd video the performance is more than enough. I never run it at that speed.

    BTW, the belts are 1:1 ratio.

    Also check that the gibs are not too loose, or too tight.

    Cheers

    Peter.


    Sent from my iPhone using Tapatalk Pro
    -------------------------------------------------
    Homann Designs - http://www.homanndesigns.com/store

  17. #17

    Re: PM25 stalling X and Y

    Is 5A versus 3.5A even a concern? Does 0 RPM hold really matter? I can't think of a scenario when it does on a mill. When I went to the MX3660 from G540 the only real gains were in the digital drivers generally just being quieter and cooler, the extra inputs were nice, but I also have the G540 on for a C axis. That's about it. I'm pretty sure I could turn the amperage down to 3.5A on the MX3660 and wouldn't know the difference. That said, i could pile a bunch of junk on both ends of my table and probably run it 180ipm all day, it's when one side sees 80 pounds and is hanging 18 inches off center that the issues come up. These smaller tables tend to flex and if the ways are a little too tight then things start to bind. Most of the time it's not an issue, sometimes it is.

    Also, Peter, thank you very much for you wiring diagrams. They saved my life (obviously being melodramatic but it feels this way) many times.

    All of that said, i still think it's a mechanical issue. There isn't a lot of horsepower and it took a lot of fine tuning to get everything working really well on my G0704. Maybe the PM is a nicer machine, lots say that it is, but getting it all "just so" made all the difference. The only time I stall steppers while milling is when I've royally messed up.

  18. #18
    Join Date
    May 2005
    Posts
    3920

    Re: PM25 stalling X and Y

    Just from a quick read of the first page here, I suspect that you have mechanical issues with very loose gibbs. The reason I say that is that you should not get any significant movement from finger tip pressure. I'd god to say that any such action like you described would indicate to me a fundamentally broken machine needing either adjustment or remediation.

    Normally when you hear about a machine that binds when outside the "middle" area of operation you think worn ways and saddles. However finger tip pressure would likely not solve that solve that issue. My first guess would be that the gibbss are so loose that the table is tipping as it moves outside that center zone.

  19. #19
    Join Date
    Mar 2009
    Posts
    27

    Re: PM25 stalling X and Y

    Thanks for the comments. I definitely agree that this is a mechanical issue, and someone who's passion is perfecting a milling machine might be able to make it work with the smallest steppers made. At the moment, I'm trying to make the hobby the stuff I can make, and not making the machine work :-)

    I have adjusted the gibbs from too loose, to too tight, and everywhere in between without making any improvement in the original problem. Note that the finger tip pressure I referred to is lifting up on the heavy end of the table to remove a bit of off balanced weight. There is no physical movement, just some pressure on the bottom.

    BTW, I did try the lower kernel freq today, and that didn't make any change.

    The motor controllers are supposed to be rated for 5.6A peak, 4.0A RMS, and that's what they're set for.

    This does bring up a question about the power supply. I'm using the switching supply that came with the package, which is rated at 48V 12.5A, and it's the typical generic box with no actual markings. I know these are not the preferred type of supplies, so that may be working against me. Now that I think about it, I'm not sure why I didn't question this previously, seeing as I have 4 controllers (one not connected to a motor), which appear to add up to well over the capacity of the supply. I probably didn't question this because it came in a package with 3 motors and 3 controllers. Could it be that simple? I would think the actual current when moving is much lower than the stationary holding current (which is reduced by the software also). I suppose I could easily unplug 3 of the controller and just run X to see if that allows it to work.

    https://www.automationtechnologiesin...or-3-axis-kit/

    Thanks,
    Rusty

  20. #20
    Join Date
    Jan 2018
    Posts
    1516

    Re: PM25 stalling X and Y

    Quote Originally Posted by 13brv3 View Post
    Thanks for the comments. I definitely agree that this is a mechanical issue, and someone who's passion is perfecting a milling machine might be able to make it work with the smallest steppers made. At the moment, I'm trying to make the hobby the stuff I can make, and not making the machine work :-)

    I have adjusted the gibbs from too loose, to too tight, and everywhere in between without making any improvement in the original problem. Note that the finger tip pressure I referred to is lifting up on the heavy end of the table to remove a bit of off balanced weight. There is no physical movement, just some pressure on the bottom.

    BTW, I did try the lower kernel freq today, and that didn't make any change.

    The motor controllers are supposed to be rated for 5.6A peak, 4.0A RMS, and that's what they're set for.

    This does bring up a question about the power supply. I'm using the switching supply that came with the package, which is rated at 48V 12.5A, and it's the typical generic box with no actual markings. I know these are not the preferred type of supplies, so that may be working against me. Now that I think about it, I'm not sure why I didn't question this previously, seeing as I have 4 controllers (one not connected to a motor), which appear to add up to well over the capacity of the supply. I probably didn't question this because it came in a package with 3 motors and 3 controllers. Could it be that simple? I would think the actual current when moving is much lower than the stationary holding current (which is reduced by the software also). I suppose I could easily unplug 3 of the controller and just run X to see if that allows it to work.

    https://www.automationtechnologiesin...or-3-axis-kit/

    Thanks,
    Rusty
    Power supply looks to add up to 600w in total. I'd say that should be adequate.
    I use my Nema23 425oz/in motors at 4.2A off a 36v/10A/350w supply (2 motors per supply) without issue. My 2 supplies are each near half the size of yours.
    You could try just running with the x'y connected as a test and see.

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