Not drawing a perfect circle

[MikeyH (Mike Hembrey)]

That effect is usually caused by:

1. Backlash
2. Improperly adjusted belts
3. Improper stepper motor parameters.

Most likely is backlash, so we can start here:

But my set screw ( grub screw ) is tight!

I often read that someone with a backlash problem says they tightened everything. When asked if they checked the set screws, they say, “yeah, those are tight too.” Sometimes they can feel tight when actually they are not. In the illustration below, the “B” image illustrates the proper position of the set screw in relation to the flat area on the shaft. Of course you cannot see this, so how are you supposed to know if yours is correct? If you try to tighten the screw in the “A” image, you will …