3018 PROver Z-axis

I started out using the stick spindle motor and had no problems. Setting the Z height with the probe automation worked perfectly. Today, I changed over to the upgraded spindle motor (the one from Sainsmart, not a larger aftermarket one). From all that I can tell it is the exact same size as the stock one, but now my material Z height comes up about .25" too high when I use the probe. In other words, when I start a drill job that was just fine before changing spindles, it now starts nibbling at the plunge about .25" too high. So a hole that should be .25" deep is now only .125".

I've double-checked my probe thickness and ran several Z probe routines and the result is exactly the same. Everything else is equal. The only thing I changed is the spindle motor. This is driving me nuts.

Check whatever it is that throws the home switch at the top of the Z-axis stroke. It sounds like it must have shifted when you changed the spindle motor.

Nope. That's not it. It's a tab that's molded into the spindle motor mount. Everything with the limit switches looks normal.

Tried a couple more things. Physically moved the spindle motor down in the mount. Z remains too high by the same amount. Tried manually zeroing the work height using a piece of paper and got the exact same results. Z height is off by about .25", so there seems to be an issue with the zeroing routine in Candle? Makes me think there's an offset somewhere, but I can't find it.

I'm completely flummoxed here. I took the new spindle out and put the original back in and everything worked just fine. These spindle motors are the EXACT same size. I measured them with calipers. I put the new one back in and it went back to pecking at the workpiece .25" too high after zeroing out the Z. Arrrrrghghghghghghgh!!!!

If it's always the same, you could program a work offset to compensate, at least until you figure it out. Here are some instructions I found for another guy I was just typing at: https://www.cnccookbook.com/g54-g92-...ts-cnc-g-code/

It seems to vary and I wouldn't call that a solution. There's a reason that the Z is not homing right.
After searching around more and joining the Sainsmart FB group, I'm not the only person that's having issues with the upgraded spindle. It seems to come down to if you try to run the thing at over about 8K, it browns out the controller and screws up the Z homing. This would also explain that when the spindle starts with an S10000 M3, it starts, hesitates then starts completely. When this happens, that's when the Z home gets messed up. If I limit the spindle to 8k, it starts normally and everything is fine.

It's super annoying that they sell this motor specifically for this machine and the controller mosfets can't handle it starting up.