Y axis left rail moves with a jerky motion

New setup on Elite forman. I noticed during assembly that when I move the gantry by hand (unplugged) that the left side was catchy and grabby along most of the travel. When moving under power it has a kind of pulsing movement on the left side up can feel in the overall machine. Also looks like the ball screw is slightly wobbly. Right side is smooth as silk.

Most noticeable in continuous mode at or above 50% speed.
Both motors working no error lights
The QCW frame is square to less than 1/16" variance.

Any ideas on where to start evaluating?


Hey Frank,

Besides a ball screw that is simply bent a little too much (should be replaced if it makes such errors, write to support@onefinitycnc.com if you cannot find another cause), I could think of point 7) (ball end nut too tight) in this document

I would also check point 4) (coupler). There was a case when a part had become loose and has hindered the rotation of the screw.

Since your machine is new, it is unlikely that it is point 5) (ball screw). However once there occured this mysterious issue. It was solved by the manufacturer replacing the entire rail.


Thx. Will check that out. Hoping the screw did not get bent.