Circles inconsistent

Sometimes they close, sometimes they’re perfect!.. I don’t get it!
Belts are nice and tight, there seems to be no play in the head, I adjusted backlash on Y to .25 which seems to generate perfect circles with no perceptible start / end point, but if I run the same file 20 times, several will be absolutely wonky… I lubricated the rails, and even checked square… everything is dead on.

Here’s a photo… you’ll see that most are dimensionally perfect, whereas I can put the cutout back in the hole and rotate it freely with no binding… but then there’s a couple that don’t close, and even one in the middle which is oddly misshapen.

This is a brand new problem, and I’ve been playing for about 8 straight hours now, and just can’t seem to make heads or tails of it.

What could cause inconsistent cuts like this?


the very top row was testing various backlash settings… the bottom 3 rows are all with .25 backlash comp on the Y axis.

Thanks Guys!

Well son of a B! I had one set screw on the pully down inside the gantry where I couldn’t reach it which was completely stripped, but Loc-Tite was used to hoild it in place, so it wouldn’t turn… So no matter how much I tried, it would not budge… The other? well, they drilled a hole in the shaft of the motor, and put a long set screw right into the shaft… that sheared in 2… But! It wedged tight enough so that on not one , but three visual inspections, and “tightness checks”, it eluded me. I finally just tore the whole gantry down. That’s when I found it!

Now I’m back to perfect dimensional accuracy, and perfect circles…


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Wow. Glad you found it and got all sorted.