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Weird Z-axis behavior!

New user here. Overall I’ve been thrilled with the Maslow, and have created several successful projects using it since purchasing the kit, z axis, sled and router earlier this summer.

Something strange has started happening lately with the z-axis, though. I’ve just noticed some odd plunge depths, and today I was able to see clearly its behavior, and can pass this example on for comment.

I mostly cut foam insulation sheets. They are 4x8 and 1" thick. Since it’s so soft, I can easily cut in two .5" passes. As long as I slow the router down to about 1500rpm, it handles foam pretty well.

Today I started a job where the first set of commands sends the sled to the start position, and the next is the first plunge to .5"

I watched the gcode in Ground Control and verified that the command said to lower .5"

As I watched the router, I saw the z-axis motor turn until the bit plunged 1.25" deep before the sled began moving, cutting through the foam sheet and the piece of backing plywood, and it continued to turn.

Even as the sled moved along its path, the z-axis motor continued to turn throughout the cut. This has never happened before. And the only reason the bit didn’t go any deeper was because it had bottomed out on the screw depth control on the router.

So to be clear, the sled was moving AND the z axis motor was turning at the same time.

On another project (plywood this time) the program had instructions to plunge .1" at a time when cutting out a circle. The first two or three passes went okay, but the next one saw the z-axis plunge at least .5" deep.

Has anyone seen this type of erratic behavior from the z axis?

Any suggestions?

Purchased kit from @MakerMadeCNC for what it’s worth

I’ve not seen that behavior and not sure what would cause it. I assume the gcode had a single plunge and then a long series of x,y moves (without a z move). My initial thought was that something happened with the encoder signals as a loss of signal would result in the motor running continuously at full speed, but you said it continued to do so throughout the cut. The runaway z-axis move would have stopped prior to commencing an x,y move (due to a quasi-timeout).

Seems a bit like a hardware problem, most likely with the motor controller board. Maybe something is shorting out pins?

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That could be caused by a loose z-axis motor cable, that is the first place I would look