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X & Y axis drifting when milling a hole

Message 1 of 3
210 Views, 2 Replies

X & Y axis drifting when milling a hole

I'm running into an issue where my bit is drifting when attempting to mill holes or slots on my older Hendricks CNC. I do not believe there to be an issue with steps as this is only an issue with this type of operation.


In this instance I'm milling a 0.28125" hole with a 0.25" O Flute End Mill using a 2D contour tool path with Ramp enabled with the defaults (ramping angle: 2 degrees, maximum ramp step: 1.5", ramp clearance height: 0.1"). I suspect an issue with the lead-ins, or with how my custom post processor is converting these to gcode. I have to set the vertical lead-in radius to 0" for my machine to work properly and this has not been an issue in the past. In this file I have set horizontal & linear lead-ins to 0" to resolve the warning "Lead-out dropped due to linking constraint". This may be a poor workflow and I'm looking for guidance on the correct way to achieve this operation.


I was milling counterbored slots similar to this last week and was running into this same drifting issue with the 0.28125" slot (wasn't experience it with the larger 0.406" CB slot, these worked flawlessly) and it appeared to fix it when setting the horizontal & linear lead-ins to 0" for 4 slots in the same tool path. Is the 0.25" bit too large to be milling the 0.28125" holes & slots?


I've attached the gcode, Fusion file, and my post processor. If anyone has any suggestions or advice, it would be greatly appreciated! Please let me know if any clarification is needed. Thanks in advance Fusion cam fam.

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Message 2 of 3
in reply to: brwoodfisher

Other notes: I forgot to mention I did run the file again and the same issue happened.


Issue still occurred with

  • Disabling lead-outs
  • Set lead-ins to 0.01 (which resolved the warning above)
  • Set lead-ins to 0.01, lead-outs disabled

However, I made a sketch on the model for a hole with diameter 0.406", duplicated the tool path, and the machine milled this hole with no drifting, and no issues at all.

Message 3 of 3
in reply to: brwoodfisher

Are you decreasing the feed speed when cutting the small hole?

The feed rate of the outside edge of the 0.25 inch tool will be almost twice as fast has the feed rate of the center of the tool


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