CNC Z axis malfunction

@dannym I experienced a z axis malfunction twice yesterday. I ran a file that I’ve run about 6 times before, so it’s been tested, and about 3 minutes into the program the machine thought the Z axis was about 2 inches lower than it really was. I stopped the program and used the remote control to manually move the Z and it would not rise higher than a certain spot which was far lower than the real Z limit.

I reset the drives, rehomed the machine and ran the program again and it malfunctioned at the same spot 3 minutes in. This time it stalled out 3 inches lower than the real Z limit.

I’ve run this program plenty of times before and have no idea why it’s having this issue. I thought perhaps my bit was getting dull which caused friction when the machine pulled upward, but when it happened again at the same spot I wasn’t so sure.

The image below is the second time it malfunctioned. I couldn’t get the Z to go any higher than that point.

Anything which jams the Z-axis so it stalls or slips will result in that symptom where the Z’s in the wrong location. It won’t come from anything to do with the bit sharpness or type.
Most likely there is something on the Z-rail surfaces that is jamming the wheels. There are other things that could cause jamming. I’ll take a look.

Thanks! The rails were pretty gunky yesterday. I spent some time brushing off the x and y rails. I’d love to know how to clean the Z axis.

They don’t see a lot of problems, but most likely is sawdust getting packed in under wheel compression. In rare cases it compresses into something surprisingly solid and stuck down. This is the sort of thing you could easily see or feel running your finger across it, also it can pack into the V-wheels. But since it’s dust, the best I’ve found is just a wet rag. Once wetted it swells a bit and lets go easily and completely.

There are some other cases. I’ve seen resurfacing of epoxy pour tables that was done too soon, before a complete cure (pours can take many days or weeks for a full cure) and the resulting flakes were compressed in there. It wasn’t that hard to get off, but wetting the rag doesn’t have any effect on getting epoxy off. Have also seen plastic flakes get in there from cutting plastic.

It’s not a frequent problem though. AFAIK this hasn’t gotten mucked in a long time.

I went over it today and the Z axis is moving freely. It has some buildup and I cleaned it, but I didn’t see enough that it would cause a problem. I jogged it pretty aggressively with no problem.

I’m just not sure, still thinking about it.

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