Backlash

Yesterday I discovered a significant amount of backlash in my Ultimaker's axes. This is how I fixed it.

First I isolated where the backlash was coming from. I used a bit of blue tape and stuck it to shafts and belts in the mechanical linkage while driving the axis back and forth with the smallest step in PrintRun. The reason for the blue tape is to amplify the small angular or linear motions enough to see them.

Starting at the motor shaft, observe the motion of the blue tape while clicking the small step left and right (X) or up and down (Y) in PrintRun. If you observe motion in both directions move to the next part in the linkage (pulley, belt, shaft). At some point in the process, the blue tape doesn't move unless you click the step button several times. The joint between the current part and the previous part is the problem.

For me, this was right at the beginning, either where the pulleys are set-screwed onto the motor shafts or the small pulley tension is set by the four motor mounting screws. So I took off the motor, removed and reattached the pulley on the motor shaft (to let the set screw get a new grip on the shaft), and reassembled it with a lot more tension in the small belts. I was able to remove most of the backlash just from that.

This also explains the flat spots I was getting when using G2 and G3 arc codes.