Bit not following the same path anymore

Have a 500x500 machine, using Universal G-Code Sender and a mix of Easel & MeshCAM

Worked well for about 1.5 of solid runtime. Changed material and now the bit will not follow the same path as the pass before. It is like it is drifting to the positive X, negative Y and even negative Z.

My first thought was that I did something wrong, but the more I test, the more I think there is something else at play.

I thought the bit I was using was dull and/or I was trying to too deep, too fast with the wrong bit. I’m new to this, so I know there will be mistakes. I have made some, like not getting the material clamped down well enough or milling the tip of one of the clamps. I even stepped away when I thought things were working well enough to, just to come back to the bit buried halfway up a clamp and the pattern being cut half on the material and the other out in open air.

I am trying to cut some letters for a small project out of 1/4" ACX that I have cut down into 8.5" blanks. It is supposed to take 5 passes to cut them out. I first thought that i didn’t set the Z correctly when it first started only taking 4 passes, then it was 3 passes. Now it is still 3 passes, but the X & Y are not following the same pass as the previous passes. It is drifting down and to the right (if you are looking from the top). I have to stop the machine because I am afraid that I am going to either break a bit (1/8" by the way) or damage the machine in some way. I have use the 1/8" single flute upcut, 1/8" 2 flute ball mill and the 1/8" 2 flute straight flute bits. The first one snaped and worried that the other 2 are now dull or something else because of this “drifting”.

There was something that I thought was REALLY STRANGE that happened. I had cancelled the program from UGS, but left the spindle spinning where it sat. I thought “well it has already cut there, there isn’t any chips to build heat from, I will see what I can find online. So I let it sit, spinning. All of the sudden I heard it touch the wood again…then again. So I pulled the bit out of the wood (using UGS of course) and moved it to a part of the wood that was untouched and lowered the bit down to the surface. In about 1 minute the bit had moved ~1/4” +X, ~1/16" -Y and just the slightest bit deeper into the wood. The drift is much more dramatic while it is cutting. This doesn’t happen if the spindle is off, it does the same thing if it manually on or automatically on.

I don’t understand how it could work fine for that long and now have some kind of gremlin take over. I was going at no more that .0625 deep, 14k rpm & up to 40 ipm. Is that too much? All of the calculations that I have found that the bits should be able to handle 60 ipm or more.

Can someone please help out a newbie?
Thanks a million in advance!!!

Stepper drift is a prime symptom of a failing spindle. As the spindle goes bad, it generates a lot of extra electrical noise that gets picked up by the drive circuit, and that translates into gained/lost steps while it’s operating. That’s why you don’t see it happening with the spindle turned off.

It’s a bummer, but Inventables will take care of you with a replacement spindle. Just send an email to with a description of what’s happening, and they will spring into action (well, during normal business hours.) :smiley: This has been an unfortunate problem with some of the 300W spindles - I’ve managed to murder two of them myself - but the customer success team has taken care of me every step of the way.

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Thank you, I’ll send them an email right away.