Roughing bit increases depth ruining the work

When using a v-bit toolpath and using a roughing bit, the depth of the cut increases and ruins the wood. This does not happen all of the time, but too frequently to be ignored. In reviewing the g code there is nothing to indicate any changes to the z axis or the depth of the cut. In the attached pictures I have the depth set to .03 and the beginning of the cut is fine, but approximately 1/3 of the way through the cut time the depth starts to increase, sometimes slowly and sometimes drastically. Also the location in which the depth starts increasing varies and does not occur in the same location or time in the defined toolpath.

In the attached pictures you can see where the rough bit (1/8" end mill) work on the top and bottom is correct and the center of the image is where the bit starts going much deeper even though not part of the defined toolpath. In a different attempt the depth started to slowly increase in the right wing of the design.

Any chance the bit is slipping in the collet?

I have checked and the bit is tight and has not moved in the collet and the router is well secured.

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Hey Kal,

if can you eliminate a loose milling bit in the collet, in theory three possible reasons could be the cause, a loose ball screw coupler, missing steps on the stepper (possibly by a bad cable connection) or a software bug. The latter seems not to be the case since you said it does happen at random, also software bugs mostly are reproducible, and your issue seems not.

A loose coupling between stepper and ball screw is possible since steel expands and shrinks with changing temperatures. Even cooling down during shipping and warming up during reception and assembly can be a cause of shrinkage and stretching, and thus of screw connections that become loose. Also heat and thus expansion could arise after a certain period of time after the start of a work process.

A loose coupler could behave like losing steps in one direction.

I would check if this screw connection has become loose. For this I would shut the controller down and power it off (or disconnect the Z stepper) and then try to move the Z slider up and down and try to listen to the noise and to find out if there is play.

If the coupler is slipping, there is a video on how to fix the screw again: Support: How to tighten the coupler on the ball screw. It shows on X or Y Axes but with Z Axis it is similar, with the difference that the coupler is better accessible, as can be seen on this video. On Z Axis, the ball screw does not need to be removed in order to fix coupler screw.

This is however in theory. It is always a good idea to first contact

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Kal, Have you resolved you issue? I’m only asking because I’m having the same sort of issue when trying to vcarve a couple commissioned name signs. I’ve also checked by z connections making sure the pins are all straight and no wires pulled out.

I believe the cause was running a dull bit a little to fast. Also I was using a 1/8 inch bit using a collet adapter. The job would run for a bit before the bit was pulled down in the collet creating the deep cut and ruining the work. I am trying to use bits with a 1/4 inch shank whenever possible.

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