Digital Depth Good, Physical Depth Wrong

If the axis is actually moving when no moves are commanded, then that would be an electrical noise issue. Check for ground loops, or other possible sources of interference and any possible wiring issues.

Hey Todd,
Thanks for working with me here. I truly appreciate your time. I have seen that sometimes having multiple components like I do ( 3 x ATTINY85 and 3 x L293D) sharing the same ground for logic and motor control can sometimes cause an issue. I have my parallel cable soldered to the control board instead of being plugged into a socket so I doubt that's the issue. Also, the BC547's that are being used to determine direction can be effected by outside forces, but can mostly be resolved by placing a tiny ferrite bead around the base ( of the BJT.

Lastly. I have just dug up an old ps2 keyboard. I only have a crap ton of USB mice. But I disconnected the speakers, ethernet and CD rom. Replaced the usb keyboard with the ps2 and am 'air milling' a test at the moment.

Yeah it's the most bizarre behavior. No problems for a few hours then all of the sudden Z is sputter when it's supposed to be locked solid. Like it'll move when it's supposed to, but then instead of locking up just does this weird thing.

anyways. Thanks again. I'll post back soon.

Best,
John

Another thing to check, an intermittent short on a motor cable can cause weird stuff to happen as well.

Funny you should mention motor shorts. Ok so just a quick recap. Going back to beginning I said that when it gets any real chatter then Z starts driving downward. So is chatter causing Z drop or is Z drop causing chatter....

OK. Just ran through a 4 hour job. The one that keeps giving me trouble. At about the half way mark everything was beautiful. I had only been milling air though. So I did what I had to do to get into position and then started at the 1/2 way point for real. No problem. Away she goes. About 45 minutes in I get some chatter and Z starts dropping again. So I stopped. Jogged Z up kicked the spindle back on and pressed against the chuck to make chatter. really making the motor work. Guess what! Z Dropped.

Figuring this was some type of feedback or other EMI interference (basically creating one huge but low power transformer here) I stopped the spindle, disconnected the power wires and double looped them through a 22mm OD x 14mm ID x 10mm tall ferrite ring. SOLVED! I can't give the spindle enough chatter to make z drop now.

This has been one hell of an experience. Absolutely maddening. I finally have my slotted spoilboard complete and now that the issue is resolved, I can get to milling some really killer stuff.

Thank you all so very much for your time and input.

Best,
John