an odd problem... mill "lurches" when changing direction.

Hey guys,

I am just finishing up an upgrade to my X3 (G0463) with the goal of extending my Y-axis travel and getting rid of grossly excessive backlash (0.018").

I replaced the Y-axis ball screw, nut, and ACBs (re-machined the bearing pockets), and added a spacer block to extend my older (pre-zero back lash) CNC Fusion Y-axis travel by ~7/8" (Crevice Reamer mod).

And now that I'm back up and running something strange is going on.

The Mill "lurches" when the Y-axis changes direction. I set up to test my backlash, and while jogging with 0.001" steps, when I change direction, the first jog lurches forward by > 0.01" and then all jogs after that are .001", unit I change direction again, where I get another "lurch"

I'm stumped :confused:


Mods... although I have an X3, I don't think the root cause is specific to the X3 platform, so I'd like to leave it here, where I'll get more responses.

add'l info....

I converted the mill using second hand, old, CNC Fusion hardware I purchased from a fellow Zoner years ago.

I had Y axis backlash problems from day one, and I believe they were mostly due to the bearing arrangement, where it appeared that the mounting block had been modified (and somewhat botched) so that the bearings did not fit well.

I switched from 28x10 bearings to 30x12 ACBs and precision bored the pockets for a slight press fit, getting rid of the slop.

The new ball screw was turned to a precise fit in the bearing as well.

So the Y-axis is nice and tight (though it rotates freely).

Could this be the result of misalignment of the ball nut mounting block?

Stiction

Don

I agree with Don, adjust the gibs.

Did you leave backlash compensation enabled in Mach3?

OOOOh.... back lash comp is still set on in Mach.... That's probably the problem....

I'll check the gibs as well.

Then I'll prop up front of mill and reach under and loosen, then re-tighten the screws to the Y block.

Thanks for the replies... I'll post results later.

Easy solutions are great ;-)