Suddenly X & Y veered off and pulled the cutter down

I have been trying to cut hexagons out Walnut. Woked fine for the first go. For the second one, Shapeoko 3 XL suddenly veered off course (see photo) and then pull the Z-Axis down along with the cutter.

Any thoughts why this happened?

Slotting is hard. Looks as if the wood grain made an easier channel for it to follow. way to address this:

  • add geometry so as to make such cuts a a pocket where possible
  • reduce d.o.c. in a slot and ensure that chips get cleared
  • check the machine electro-mechanically before each cut (wiring all connected, belts taut, set pulleys present, tight, and one against a flat)

Esp. check the belt tension.

Also, rotate either your model or your stock 90 degrees so that you aren’t cutting directly with the grain.

Cutting with the grain for a slot should be totally possible. I do it all the time.

Did the cutter pull out of the collet? If so, then your collet is not tight enough. If the Z axis was pulled down then I would check the pulley and belt on the Z.

Otherwise you lost steps for some reason, or had a glitch in the controller. Are the belts tight enough? Are the pulleys tight enough?



My design and G-Code generation was done with Carbide Create w/ material set to Hardwood

  1. I was using Outside/Right option. Not sure how Pocket helps. Happy learn.
  2. DOC was set by Create

Both. First Z-Axis and then collet.

When you’re cutting a slot, the bit rubs on both sides of the cut, and there is nowhere for the chips to go that they will not be re-cut if they aren’t evacuated.

Adding offset geometry at a distance of twice the endmill diameter or so addresses both of those conditions.

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Slotting can be tricky with deep cuts. I cut hard white oak a lot and normally do a 4mm doc so when the slot is first starting chip evacuation can be tricky until the slot is long enough for the chips to shoot out along the cut path. I normally use a vacuum to clear out the slot each pass.

I’m having trouble understanding how slot problems can be avoided with pockets. Isn’t the first cut when starting a pocket going to be a slot?

FWIW, I haven’t had any problems with slots yet, but always looking to improve my toolpaths.

Yes, but then at each next depth, you’re only touching two sides of DOC, for a slot you’re touching two sides all the way down. Some CAM’s let you do the outside or inside cut with an extra pass so that you can have the slot away from your part and the cut next to your part with only 10% engagement or some low number like that.


I have to agree with foreman. I slot all the time in hard woods and with grain, deep depths of cut and only had this problem one time and it was do to belt tension. The bit pulling out of your collet is simply not being tightened enough. Go through your belts and v-wheels to be sure the arte set properly and always be sure to tighten your collet good and tight. G/L Ray

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I concur with Tim. I had something similar to this occur recently in MDF on a profile cut, which you are doing, so I would not suspect the grain causing the issue. Cleaned my collet and haven’t had an issue since.

What were the feeds and DOC?

I took the defaults generated by Carbide Create.

Can something like SuckIt or running a vacuum as it is cutting help with the issue of chip clearing?

Yes, a vacuum and dust shoe will help with chip clearing. List of designs here:

Detailed discussion of drawing up and cutting a design here:

The feed and DOC look fine, how sharp is your endmill?

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fairly new. I have used it to slot some pine. less than 1 hour of use on wood.

I figured my experience today might be worth sharing on this post. I have been having a go at making my own dust boot out of some 20mm acrylic like material. I had done a number of cuts and had one last pocket to mill. A circle for the vacuum hose to go from. Every time I went to run the action, it failed and pulled the cutter in a direction or went wrong. I spent a hour checking belts, re-making the code fiddling - trying it again and a again - with the same results. Each time no change. I then decided to change my end mill - even though it looked fine. As soon as I did that it cut perfectly.

No rhyme or reason, no logic as each cut previous had been fine - but once it was changed it worked a treat.

A sharp end mill is a happy one, and many of these end mills from china etc just do not last long…

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