I put in gcode with nice round circles, and this is the part I got out. (see image) It is "stretched" along the y axis. This is 6061 that I cut with a .125in 2fl endmill. What is going on? Is my x gantry flexing and collapsing slightly as the tool cuts?
Does it cut correctly in a softer material like plywood? Are your steps per mm calibrated correctly? What are your speeds and feeds? What's your depth of cut and width of cut? What machine? Belt or screw driven? This is a common problem but as you can tell, it can be any number of things. We need more info to help.
I haven't cut anything this small and precise in softer materials, so I don't know for sure but I haven't noticed it in the round plywood parts I've cut so far. If I have a chance today I will cut the same part out of ply to test Here's the other information: Are your steps per mm calibrated correctly? To my knowledge yes, and since the accuracy on the Y dimension of those holes is good and consistent on all four I am thinking that is a confirmation that the calibration is ok. I'll check it today What are your speeds and feeds? What's your depth of cut and width of cut? .5mm stepdowns Width of cut: those were all contour cuts, so .125" Machine LEAD
"To my knowledge yes, and since the accuracy on the Y dimension of those holes is good and consistent on all four I am thinking that is a confirmation that the calibration is ok. I'll check it today " If you didnt go through calibration and are using the default settings, that's probably your issue, or at the very least, one of your issues. The default settings are a starting point. Every machine is different due to the way the screws are made. Before doing any test cuts, calibrate. Another thing to check is your lock collars and your motor couplings. Make sure they are secure. Its common for these to vibrate loose after install.
that shape circle means you have backlash. The tool is rotating so it tries to push itself to one side. if any gantry can move in that push direction then it will move and you will get oval cuts. so, use a finger to push on the tool in X direction and in Y direction (stepper power on, spindle off). it will move more and more easily in one of those directions. fix that (-: as mentioned before you need to check that all motor adapter collars are properly secured though your photo does not look like a motor collar slip, check it anyway.
