Yes, it looks like one axis has some play in it or backlash.
I had discovered some issues I was encountering on my machine which mostly were corrected after tightening up some screws, but I still see that though most cuts have improved significantly, my machine still doesn't cut an exact circle when I attempt to do so. So that you know what type of machine I have and what I am experiencing I will submit a brief summary of my machine, its electronics, hardware & software, include a picture of it, and include a picture of the result of the piece I just cut which is not perfectly round. Any assistance you might be able to provide using the information I have provided would be appreciated. I'm thinking it may still be some loose screws or that I possibly don't have one of the motors set exactly correct regarding steps/unit. I still have to go back and check the latter as I switched it once and attempted quickly to return it to the settings it had originally.
I built my own machine. It has an ESS ((Smooth Stepper) motion controller connected to a PMDX-126 BOB. I’m running a three axis machine using Mach 4 controller software. The external drivers are all DM542T stepper drivers with dual 425 oz-in NEMA 23 steppers driving 2010 Ballscrews on linear rails. The X axis is a smaller torque NEMA 23 driving a 1605 ballscrew on linear rails and the Z axis is a NEMA 34 driving a 1204 ballscrew on linear rails. The frame is made of 80/20 aluminum extrusion (profile 3030). I’ll include a photo:
0836764C-5E58-4547-B296-0A86E081EDA1.jpeg4032×3024 3.41 MB
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Yes, it looks like one axis has some play in it or backlash.
Gerry
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Yep, a typical case of backlash.
Cheers
Roger
That looks a bit extreme for backlash, which is typically under a mm or so. If you've ruled out confusion in the units/mm settings, I'd suspect some mechanical issue, either loose screws or (more likely) loose pulleys. When a set screw develops some play in it, it's not always obvious; it only lets go at the extremes of motion, and then goes to the other end of its range. Try making a mark on the shaft and pulley with a Sharpie, and run your program again with a piece of scrap. Inspect your mark for discontinuity as the program progresses. If you find this is the problem, make a flat on the shaft so the set screw can't drag itself around to various positions when stressed. .
[FONT=Verdana]Andrew Werby[/FONT]
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While i have zero real world build or use experience, as I have not yet jumped in....
Shouldn't the first piece of troubleshooting be to use an extremely light cut in a soft material, or even chuck up a sharpie and draw on some paper? The results would be extremely telling...
There is an "issue" with mach and some drivers, where the drive will not catch some slow moving steps sent by mach - usually these are at the transitions of an arc.
In mach3 the way you would fix this is by setting it to sherline mode, which changes the pulse pattern from tiny pulses, to half waves. I dont know if mach4 is the same
This is the first place i would look if i was getting "backlash" like that that did not appear to actually be mechanically induced.
Oh, I agree entirely with Andrew: 'backlash' due to a very loose coupling or similar. Could be almost half a turn of the ball screw in fact.
There is an "issue" with mach and some drivers, where the drive will not catch some slow moving steps sent by mach - usually these are at the transitions of an arc.
For cases where a single pulse is being lost, this is usually solved by flipping the default state of the Step pin. Tyhe problem there is timing constraints in the power driver electronics.
Cheers
Roger