HobbyCNC microstepping problem

Sorry had a brain fart on the backlash.

Ok so lets suss this ok.

Steppers off mill you get full movement, no "missed steps" or anything like that ?
IF THAT TEST FAILS: That would indicate an electrical or stepper issue.

IF THAT TEST PASSES: I would postulate you have a mechanical issue
  • Gibs are too tight.
  • If the leadscrew nuts have adjustment they are too tight.
  • There is end play in the bearings, which would be rare on all 3 axis.
  • Backlash is an issue, after a quick search 0.003" or 0.0762mm seems typical backlash for a Taig mill. 0.040mm - 0.050mm appears to be quite a
    bit on the low side.
I would also test with backlash comp turned on and see if that makes a difference.

On my mill I running ballscrews with a 5mm pitch, with 1.9' stepper and 1/8 microstepping I get 0.003125mm per step. Now from memory my backlash is about 0.015mm so without backlash comp on I'd get 4.8 turns before any movement when reversing direction. Yep I know I can get better with a double nut or oversize balls but I'm happy with the way my parts are coming out.

I had a real issue with mine to begin with that had me stumped for a bit, which turned out the lock nuts supplied weren't the best quality, changing to a better locknut fixed the issue.
 
You could remove a stepper but leave it electrically connected and then see if you have the same problem when it does not have to move a load. This should be a definitive isolation between Electrical and Mechanical.
 
Boswell said:
You could remove a stepper but leave it electrically connected and then see if you have the same problem when it does not have to move a load. This should be a definitive isolation between Electrical and Mechanical.
Click to expand...

That's exactly what I have suggested.
 
bladehunter said:
Ok so lets suss this ok.

Steppers off mill you get full movement, no "missed steps" or anything like that ?
IF THAT TEST FAILS: That would indicate an electrical or stepper issue.

IF THAT TEST PASSES: I would postulate you have a mechanical issue
Click to expand...

I will remove a stepper from the mill and test it after work today today to eliminate any mechanical effects as you suggest. I'll look at backlash and other mechanical issues only after geting the steppers to run well.


Emil
 
I removed on of the steppers from the mill and testet it. The results match what I observed with the stepper on the mill, but the problem is a lot easier to see.

When using 4 microsteps it will run like this for each microstep I jog it:
Step CCW (medium size)
Step CCW (large)
Step CW (small)
Step CW (small)
This sequence then repeats consistently when I keep stepping.

Looks like a wirering problem, but I don't think it is. I have measeured the resistance between the stepper wires to verify that the wire colors from the datasheet are correct. I have tried every wirering combination which makes sense, with the same result in each case.

I didn't have time to measure the voltage each phase is geting last night, but I will do that today.


Emil
 
bladehunter said:
You haven't got your step & direction pins mixed up in Mach 3 config.
Click to expand...

Good sugestion. Had to check that.

Got this in LinuxCNC:
Pin 2: X direction
Pin 3: X step
Pin 4: Y direction
Pin 5: Y step
Pin 6: Z direction
Pin 7: Z step

It matches the pinout in the HopbbyCNC manual, so that is not the problem.
 
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