Job accident with weird movement

Hi all,

While cutting some parts for spectacle cases, I had to whitness the job fail and see the machine doing an unexpected, very fast movement into an unexpected direction.

The job was on its last round of the cutting contour toolpath (cutting the last 0.5mm), with the tabs being 6mm high and 5mm wide (18mm stock). Suddenly, something of the cut part broke, or maybe one of the tabs broke, I don’t know. However, the inner cut parts started moving and clogged the way of the mill, while it was at tab-depth.

I’ll have to figure why the parts broke (I suspect a tilted z-axis), but what I do not understand at all:
Why on earth did the machine make this rapid movement to the left (marked on the images)?
The clamped down stock moved like 2-3mm during that accident, but there was no reason why the machine would move into a negative X-position. I don’t know what would’ve happened next, because I already interruppted the power.

Does anyone have a clue about what could have caused this movement?

This was probably caused by lost steps — you seem to be cutting a slot just as narrow as the endmill? That results in near constant 100% tooling engagement which is rough on the machine to do — best practice is to add geometry and cut as a pocket down to tab depth or the penultimate pass:

1 Like

Thanks for the suggestion Will, I will try that to be more safe in the future.

Regarding the lost steps: When losing steps while moving to the left, shouldn’t the router end up further to the right, rather than further to the left?

Also measured my spindle mount: It was 1mm lower on the right than on the left. As I was also using an upcut mill, this could have been the reason why the tab broke. The tip of the mill basically would have been slightly cutting “under” the tab, then pulling on it while rising to tab height.

Sometimes the machine will gain steps because it is pulled into a cut.

I like using downcut Endmills in wood, esp. when using tabs.

1 Like

What Will suggests is most like true but my Shapeoko XXL once went crazy and started cutting just like yours and ruined the project. The thing just started out full depth out the outside of a cutout around a box in one inch material. Fortunately it has never done it since. :rofl:

You’d be amazed how much force the router and bit can exert when cutting. So quite possible the bit grabbed the material and pulled it over. Keep in mind since you’re cutting a slot the bit is pulling and pushing against almost 270 degrees of material, so it’s possible it also went left instead of right which you might think due to the rotation.

Recently ran into the issue with not having a collet tight enough and pulled the bit down. You see it all the time on the forums but I was shocked how far it actually did pull it down into the material.


I have had the same thing happen on my machine a few times. Every time was during (relative) aggressive cuts in hardwood so I am curious if this is a result of some sort of overheating on the control board?

1 Like

That would actually surprise me in my case.
I’ve been using the same feeds and speeds during summer and now the temperature in my shop is much lower.
But it fits to what Will said, regarding the bit getting pulled into the material. Would assume that can happen too, when being too aggressive.

@Deerunner Ha, that happened to me in one of my very first jobs as well. I saw it and thought like, no this cannot happen! It took me a few seconds to realize that it was actually happening before I shut down the machine. The bit almost left the collet :astonished:

1 Like

This topic was automatically closed 30 days after the last reply. New replies are no longer allowed.