Total newbie here; feel free to ask me the dumb questions, 'cause I may be doing something utterly stupid here.
Ran into the problem on firmware version 0.14.17. Still see the problem on 1.0.0.
The cut not-quite-a-circle appears to be rotationally symetric; cut it in half, rotate one half 180-degrees around, and the halves would match up.
It appears to be repeatable. Cutting the hole by helixing down, and cutting the bottom flat yield the same not-quite-a-circle shape. Cutting circles at a couple different sizes yields the same not-quite-a-circle shape.
The not-quite-a-circle seems to be elongated along a line parallel to Y=2X or something. It's not elongated along a single axis, so I don't think it's an incorrect thread-pitch in the config.
I ran the machine through a circle without cutting anything and it just looked "jerky" to me. It didn't seem like a smooth circular motion with both axis in constant motion; it felt like each axis would stop too abruptly in their motion instead of making that smooth sinusoidal swaying motion I would expect.
Cutting a circle with outside radius (including the 5/16" endmill size) of 0.75", the outside diameter varied from about 1.52" to about 1.47". (Inexpertly measured, but it's enough you can see it clearly.)
Very light, slow cuts in aluminum with a HSS 5/16" endmill.
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G20 ( imperial ) G90 ( absolute coords ) F2.500 ( set feed rate ) G0 Z9.700 ( move to safe Z ) G0 X2.2083 Y2.237 G0 Z4.340 G1 Z4.090 ( Helix down ) G2 Z4.060 I0.4437 J0 P2 ( Flat bottom ) G2 I0.4437 J0 ( done ) G0 Z9.700 ( move to safe Z )
This is on a Grizzly G8689 converted to CNC using the HeavyMetal CNC X2 kit, with 570oz-in 3.5A NEMA23 steppers on all 3 axis. My Y axis is my shortest, with only 3.0" of travel after the conversion.
If there are some diagnostic shapes I should cut to help narrow down what's working and what isn't, that might be helpful.