Touch Plate accuracy issues?

I am experiencing something weird when zeroing Z with my touch plate.

Usually the bit will retract 50.8mm (2”) after touch off, this is also what the setting is in Mach 4.

Just recently though, it started to cut shallow and I noticed that the bit only retracted 38.8mm instead of the usual 50.8mm, My cuts were also left shallow by 6.13mm.

On testing, I note that when starting the machine and Mach afresh, the bit will retract the 50.8mm after zeroing, but will leave the cut 6.13mm shallow, and then the retraction height is again only 38.8mm I can verify this depth by touching the bit to zero on the table and this is the difference.

If I just set the tool zero manualy by touching on the table and setting the Z to zero in mach, the cut is perfect.

I haven’t updated any software recently and the computer is quarantined from the internet and the Avid setup software (to turn off many programmes and settings etc, can’t remember what it is called) was run when the machine was setup.

The machine is a 4’ x 10’ Pro has NEMA34 motors and is approx 5 years old and it is run in a semi production mode, e.g. most every day, but was certainly run harder it’s first few years.

I have scratched my head trying to figure out what may be the issue, I’m convinced that it must be a software thing, but of course may be way off?

Hoping that someone can point me in the right direction, for now I can continue working by zeroing manually but have gotten so used to the touch plate that I really miss it.

Thanks
Gus

Several versions ago on Mach there was some unreliability issues with the touch plate due to a bug in Mach’s motion planner.

What version of Mach are you on now compared to our latest available for download?

If you’re on an older version I would upgrade and see if that fixes the issue.

Thank you Eric for the reply, much appreciated.
Yes, my versions are several versions old, I am running Mach 4 build 4612 and Avid ESS 277.1.
These have been flawless for the last few years and I am hesitant to mess with the software, as I recall it was a little involved getting everything just right last time I did it.
I will mess around with checking everything on the touchplate side of things, cables, connectors settings etc etc, but if no luck in resolving it I will definitely do the software update.
Thanks again
Cheers
Gus

Sounds like you’re on a much older build. if you check here:

Around 2.4.3 we found a bug in Mach for Z probing and fixed it.

If you want to try a new version but keep your old one you can backup your Mach4Hobby folder (you can just rename it to something else) and you can reinstall Mach and try the new version.

As you can see there’s been a new set of bugs with each version that we’ve gotten on top of. My sense with the latest version is that it’s reasonably stable for most people. I would try that one.

Brilliant, thanks again Eric.

Cheers
Gus