Z axis position loss

I am having an issue where my Z axis loses its position and seems to move too far upwards for reasons I cannot decipher. It seems to grow progressively worse as the scallop toolpath passes over the same area.

Occurs about 150k lines into a 35 minute scallop toolpath written in fusion 360, when the tool is supposed to be moving mostly vertically up the wall of a piece, shown here:

Speeds and feeds:


I realize that my transition/lead in/lead out feedrates could be high, but it seems to occur in an area where that isn’t a concern

Short clip of my timelapse showing the position loss: https://youtu.be/6iLjjdUK9HM

Snippet of my .tap file where I believe the failure is occurring: Copy of SampleZFail.tap - Google Drive

Would be interested to know if anyone has had a similar problem or has any idea why this is happening.

Those feeds and speeds look just fine. I know @jjneeb has run into this before and I believe has a fix for it, I believe it depends on what setup you have.

You can also contact support too.

Have seen this on half a dozen machines that are doing these 2.5D carvings.

Try switching your Z axis Step signal active level to the opposite value ( I think it is active high by default, but I don’t have access to my machine right now to verify). This is in the plugin pins configuration area.

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I bet you have yours set like this Jim:

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Thanks so much @Eric and @jjneeb ! From what I can see this is flipping the output for controlling the z stepper, what effect does this have on the machine and why would it fix the issue?

Correct, it is inverting the polarity of a step pulse. In the end, you get the same number of steps either way. However, I think there is probably a marginal timing or voltage level between the ESS and the stepper driver, but I have never pulled out the oscope to really dig into it. I had this issue several years ago, and AVID recommended trying it. It fixed the problem and had no side affects that I have ever noticed. I have recomended this to a half dozen other people who have had the issue and it has fixed it for them as well.

Whats also strange is that I’ve never had the problem with X or Y steps drifting like that, only Z, and only in the up direction.

That config Eric showed above is the correct one - I just got to the hotel after a roadtrip through a Nebraska/Kansas/Colorado snowstorm and checked it on my offline copy of Mach4.

Thanks! I will try that fix!

My version of mach4 with the avid rotary screenset seems to be missing that “pins config” window, is it under configuration? I can’t find it.

In the Mach 4 menus, go to Configure → Plugins → ESS.

Thanks! Trying it out today.