CNC Router Super Jerky


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  1. #1
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    Default CNC Router Super Jerky

    Hoping someone on here can help me,,, I posted this over on the Mach3 forums as well, but figured I'd try everywhere. My CNC router is super jerky,especially on curves - something similar happened berfore, and Ger21 figured it out, but now its acting up again, a little differet this time,,,

    I have a 4x8 CNC router Ipicked up a couple of years ago - it's a home built jobber by somebody, steel frame, and not the best design. I have used it a lot though, and have been nursing it along - hopefully I'll be able to replace it with a better one, but I'm not there yet, so need to keep this one alive for a bit longer if possible.

    The latest 'upgrade' I did to it was to replace the Z axis to a better setup, which seems to be working fine, and to regear the X axis/the motor driving it across the gantry. The old design (and still currently my 'Y/A axis), ran on direct drive rack and pinion. The backlash in the direct drive always gave me problems, so I swapped the X axis to a CNC routerparts 3:1 belt drive reduction unit, which holds the pinion against the rack under spring pressure. I recalibrated my steps, and gave it a test. It jogs just fine up to 600 IPM or so, maybe faster, which is plenty fast for me. It moves around by hand, with no power to it, without binding. But when running G code it acts horrendously. On curves it stutters so badly the machine is shaking. On straights it runs better, although still a little rough, but every now and then it still jerks - especially when it''s approaching a corner, but sometimes in the middle of a straight. It does it in the X axis, and the Y axis. I think the Z is fine, although it's hard to tell since it moves so much less.

    I am running Longs DM542a drives, with a DB25-1205 breakout board. Windows 7, 32 bit, Mach 3, no external motion controller, just running off the BOB. Motors are NEMA 23 23hs45-4204s like these:
    https://www.amazon.com/Torque-Steppe.../dp/B00PNEPW4C

    I have my kernel at 25000, but have tried it all over the place with not much different results. I've tried my microstepping in a few different configurations, including 400 or 800 for the X axis (the one geared 3 to 1 with a 1" pinion, 20 degree pitch on the rack) and 800 and 1600 on the Y-axis. I'm not exactly sure what this equates to in terms of microstepping (can someone elaborate on that?).

    I think it has to do with my computer, or maybe my BOB died... I had a similar problem before when the computer was trying to talk to windows and update itself when I had it networked. Now it's disconnected from the internet. I have run the drivertest file, and it hovers around 25000 pretty stable. My CPU usage doesn't ever seem to spike over 12%.

    I've tried it on multiple G code files, all which I've ran before with no problems.

    Argh, any idea on what's causing this now? I'm going a little crazy. Can anyone tell me where I should set my kernel and microstepping for a good/conservative start? somewhere that it 'should' work with velocity around 200 IPM? And why does it do it only under G-code, but not while jogging? Ugh...

    EDIT: Also, CV mode is on, and look ahead is 200.

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    Last edited by dameronw; 06-01-2017 at 03:43 PM.


  2. #2

    Default Re: CNC Router Super Jerky

    It sounds like you need to change your Motion Mode. Go to Config>General Config dialog box and check the Motion Mode is set to Constant Velocity, not Exact Stop. On the right there will be CV control. You probably should uncheck any of these. There is also a box somewhere in the middle that says Look Ahead. If your computer is reasonably fast, you should type 190 or so in the box instead of 20 that is the default. Maybe that will solve your problem.



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    Default Re: CNC Router Super Jerky

    Just went and double checked - CV is checked, and on the right hand side none of those options are checked. My 'look ahead' has always been 20, and I know my computer isn't the best, but in any case I went ahead and tried it both ways, and no difference. Yuk

    I still think it may have something to do with kernel, microstepping, pulses, etc. but maybe not,

    Dameronw



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    Default Re: CNC Router Super Jerky

    Go to the Settings page and make sure CV Distance and CV feedrate are turned off.

    Gerry

    UCCNC 2017 Screenset
    [URL]http://www.thecncwoodworker.com/2017.html[/URL]

    Mach3 2010 Screenset
    [URL]http://www.thecncwoodworker.com/2010.html[/URL]

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

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


  5. #5

    Default Re: CNC Router Super Jerky

    Check this on ArtSoft forum:

    CNC router shudder and jerky / jitter doing 3D toolpaths

    Or do a search for AlexanderJamesGuitars on the Artsoft forum.

    Read it all. Especially the parts where it talks about your gcode turning off your constant velocity and look ahead with a G08 command.



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    Default Re: CNC Router Super Jerky

    I has same problem it was computer causing problem and also could be motion board but more then likely computer I had to reinstall mach and disable Antivirus sounds stupid but worked

    Sent from my Le X820 using Tapatalk



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    Default Re: CNC Router Super Jerky

    Also make sure cv is on

    Sent from my Le X820 using Tapatalk



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    Default Re: CNC Router Super Jerky

    Quote Originally Posted by X07gavrp View Post
    Also make sure cv is on

    Sent from my Le X820 using Tapatalk
    Sorry scrap cv bit just seen ur edit

    Sent from my Le X820 using Tapatalk



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    Default Re: CNC Router Super Jerky

    Hi, my advice for what it's worth, and as I've been told, is to run your computer completely naked.......LOL.......that means no antivirus, no internet and no MS Office etc etc........just the Wind op system......do all your G code compiling, if you're into manual G code writing, on your desktop computer or a separate laptop using Notebook and save it to a USB flash drive not the computer HDD which only needs to be a small one.

    This keeps your machine computer isolated from any virus attack you might pick up from the net or files that have been exposed to the net.

    When all else fails, scrap all your "dodgy" files, reformat your machine computer HDD and ALL flash drives, reload your Win system and the Mach 3 files, XML files and drivers etc.....NOTHING ELSE......that will be one unknown factor eliminated.

    BTW.....don't ever use files from another person who doesn't believe in computer cleanliness, create your own or with proper bought in CAM software.

    The other thing is it could be a mechanical problem....you might have dirt in the linear bearing blocks or ball nuts.....or some dirt in the rack teeth.... but that is an easy solve to do.

    With the power off rotate all the stepper motor spindles to see if you get a tight spot anywhere.......check the couplings too......being a big home built job you might have some misalignment from the frame flexing on an uneven floor......a bolted frame is extremely prone to that.
    Ian.



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