Z axis pulled strait down mid run

I was running some back side machining in freshly made soft jaws and had a strange failure mid job. The first op went smooth and on the 2nd tool path one piece pulled out and dropped. OK no problem will move the mod vise in more and make sure they are clamped tighter and run a lower optimal load. I let it keep going to try and salvage the 2 other parts and the next part started cutting fine but then it pulled the Z axis down like nothing without even a peep from the steppers and stalled motion in X, Y, and kept pulling Z down.

There was no chatter or skipping sound from the steppers “granted I haven’t crashed my HDM before so I don’t know how loud the steppers get on it when they do miss steps but on my So3 it was very noticeable when it skipped steps” it didn’t pull the work piece out of the soft jaws or pull the tool down in the collet.

I feel like there is no way it should have been able to pull the Z axis down before pulling the part loose in this situation.

My gut says have someone check and tighten all 4 ball screw couplers because the only sound was the cutter.

2d adaptive 20k rpm, 50 ipm, .145" Doc, .050" optimum load climb .0025 chip load

Has anyone had this happen on their HDM?

It happens at the end of the video to save you a few minutes if you don’t want to watch the whole thing.

Check the wiring connectors for the Z motor you may have a bad connection.

Anthony

Did the failure happen in the same place both times?

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That was the first run because it damaged the soft jaws and I needed to mill another fixed side before I ran it again. I just happened to be recording during the failure so I figured I’d upload it so others can see what im talking about.

I made a new soft jaw this weekend and ran the job again with less aggressive feeds and ran it mid air first to see if it would do it again without a load. The CM preview and Fusion 360 simulation look good so I installed a new end mill and re ran the job without a failure.

I just don’t understand how it got pulled down and stopped motion in both X and Y without making any noticeable sound of skipping steps. I tried to check the Z axis coupler on my own but could only get a allen key into the bottom bolt which was tight. The top bolt was too high and blocked by the stepper motor mounting block so I have to wait for help from a friend to address the couplers.

I feel that the lightly secured part would have come out long before there was enough force to back drive the Z axis.

I’m just glad it was a budget end mill and not one of my Amana bits that got wrecked and the SMW jaws can be flipped provided you don’t cut super deep into them.

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