fadal 4020 Z home position issue Need Help

I'm running a fadal 4020 we reset the Z home position ran out that job set up another mid way through the Z home position is going about .1 above the cold start line. I has happened twice with the same results.. any advice is welcome.

Thanks
Kling

Old Fadals HS88 will cold start at the nearest marker pulse, so you may just be cold starting to the next revolution of the motor.

At the start of the job we are at the Z cold start position, where the line indicates.. We ran 50 parts just fine, then on part 51 machining was done about .1 about the part. When we went back to the cold start position and the spindle went to .1 about the hash mark, then at this point it won't tool change either.. So it was working and midrun changed its home position. Hopefully this makes more sense..

Slip of shaft? Z motor coupler or endcoder? I would tighten both.

There are just quite simply way too many things that can cause an issue like this .100 is a **** ton of movement, so ifizcnc might be on to something. It would depend on your machining conditions. Less than ideal tooling with aggressive feeds could theoretically cause this issue, with a motor coupling slip. The Fadal servo motor coupling design leaves a lot to be desired in my opinion. It is VERY unlikely that the coupling between the motor and the resolver is loose. A bad resolver can cause this, but with some testing this could be confirmed quite easily (move, home, move, home, move, re cold start, move) ect. You need to put an indicator on the machine and check it out, with no load (not cutting) if there is a variation it is most likely the resolver. If the problem only occurs during machining, it is most likely tooling/mechanical.

thanks all I will let you know what I find