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Topics - dameronw

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General Mach Discussion / CNC Router Super Jerky
« on: June 01, 2017, 01:56:56 PM »
Hoping someone on here can help me,,,

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, 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, or 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:

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...


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