More ovals -- even after new set screws

I was super excited to cut my first aluminum last night. I researched my speeds and feeds extensively and was happy with how easily I was able to get the machine to work.

I was cutting Aluminum Flat Bar, 1/4" x 4", 6061 General-Purpose Plate, T6511 Mill Stock with Kodiak Cutting Tools KCT166406 1/8 End Mill. I was cutting a 5 mm holes using 10k rpm with a feed rate of 500 mm/min and plunge of 120 mm/min for a boring operation in fusion 360 with a pitch of 0.5 mm.

Just because I was nervous, I only drilled down 2 mm and the whole operation was super fast and easy with nice circles. Confident, I increased my depth to 5mm but the resultant boring operation produced ellipse bigger than the hole with the major axis in the y direction. I had this problem before as mentioned in Strange Behavior - Shapeoko cuts Ellipse, not circle.

I did the machine checklist, replaced and tightened the set screws, cleaned all the interfaces between the belts and the machine.

Any ideas?


Can you flex your z-axis about the X-rail? Grab the bottom of router and pull and push along the Y-axis.

If you’ve thoroughly ruled out all of your set screws and pulleys, maybe you’ve got slop in your Z-axis?

Even check that your Y-plate screws are tight into your X-rail. A little slop there could cause the rocking back and forth?

1 Like

And after you are done with the mechanical checks, check your belt calibration params too ?
i.e. when jogging by e.g. 1inch along X or 1 inch along Y, does the router actually move by exactly 1 inch? If the size difference in your oval between the X and Y dimension is not a lot, it could just be that a little belt calibration adjustment is required.

Can you cut perfect circles in a soft material ?


Thank you very much for your quick suggestions. I continue to be inspired and impressed by this community.

Next steps:

  • Check for y-axis slop
  • Check all set screws and pulleys to include y-plate screws
  • Check belt calibration params
  • See if I can cut perfect circles in soft material

I’ll try this tonight and post results here.


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