[Bird_E]

So I need some ideas as to what is causing a strange backlash type issue with my Z axis. I have just finished an RF-45 style machine conversion.
The Z axis is driven by a 3/4" ball screw and double circuit ball nut.

When I got the machine working and under power I checked the axis for backlash and found something strange.

If I setup a test indicator and touch off on the spindle nose and jog down a few thou, zero the indicator. Set mach3 for step jog @ .001. When I press the key to move the head up, it continues to move down about a .0015 before it starts to move up!! Traditionally I would think backlash would show as zero movement on indicator until the backlash it taken up and then start movement in opposite direction. In this case, when direction is reversed, movement continues in the same direction for about .0015 then it reverses.
of course I checked to make sure the pulley and motor are moving in the correct direction, which they are.... Any idea what I should be looking at?
Thanks!
Bob

[aarongough]

After it reverses and moves in the direction you expect, does it move the amount you expect or does it move less?

[TechGuy5002]

Is there any play in the Ballscrew between the bearings. Can you jiggle the ballscrew?

[txcncman]

Play in the Z axis coupler. Play in the screw/nut connection. Slip stick on the Z axis ways/bearings. Flexing of the frame.