I think I figured out where the problem is coming from. I disconnected the lead screw of the x-axis (long axis) from the gantry such that the gantry could slide freely in the x-direction. I then did a G0 rapid on the x-axis such that if the leadscrew were still attached to the gantry it would go 40 ipm (400 rotations per second for my leadscrew). At this speed, it is easy to watch the leadscrew and see if it is out of true. I found that my leadscrew wabbled a significant amount indicating that it was not straight. This means that the nut is subjected to a sine wave like friction force (as the leadscrew moves further and closer to the true alignement position of the nut). I'm almost positive that this sine way like force is the cause of the noise! I'd be interested to know if you see this behavior as well.
Also, do you get noise from any of the other axes? |