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Slipping/losing steps in Z axis

From the original Synthetos forum (2011–2025)

Started by jeromio on in TinyG Support. 1 reply, last activity May 3, 2017.

jeromio #

I have a consistent, tho unpredictable problem with my Z axis. It will lose steps, randomly, in either direction, altho it seems to happen most often going down. My Z is a ball screw and it can be turned easily by hand (I have a 3" knob on the opposite shaft of the motor).

I have isolated the wiring so that nothing touches and the AC cable for my router is far away from stepper cables.

I have bumped the max accel down to 5million. I use very slow feed rates for Z: was using 100, have gone down to 50 with no change.

But here's an interesting aspect of this problem. If I rest my hand on the knob as it is moving (when it's just doing a very slow, 2mm change), if I apply slight rotational pressure, I can easily move the knob until it reaches the correct number of position. Then it will "stick" there and hold.

So is there a setting I should adjust? perhaps the trim pot for that axis needs more or less current? I have a beefy 24v power supply. The X & Y axes perform very repeatably and do not lose any steps.

I'm also going to try switching motors (they're all NEMA23s) to see if perhaps there's something amiss with the Z motor.

cmcgrath5035Staff #

It should be easy to eliminate router noise form the discussion by running up and down with spindle off. From your discussion, I think you have already done that.

If I rest my hand on the knob as it is moving (when it’s just doing a very slow, 2mm change), if I apply slight rotational pressure, I can easily move the knob until it reaches the correct number of position. Then it will “stick” there and hold.

Have you tried rotating the Z between steps when it is not moving, i.e. is it easy to break the hold position with the hand wheel?
Easier to do this up vs down?

What are your Z motor and axis settings?

Most ballscrews have larger travel per rotation that the threaded rods or ACME screws typically used for Z. The result is less mechanical torque amplification for the Z axis, meaning you might need more stepper current for Z if that is the case when using parameter sets intended for the ACME set ups (or rods) that are more typical.

Reducing Z axis microstepping to 4 or even 2 might help as well, assuming you are using 8 at the moment.

How how heavy is your spindle (router)?

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