Ideas needed: techniques to reduce Z axis slop:

Ideas needed: techniques to reduce Z axis slop:


Guys,
I have a backlash issue in my Z axis and here's the background:
Its a Bridgeport CNC Series II with a 2:1 pulley reduction from the
stepper to the knee driveshaft.
The shaft then goes into 2:1 ratio 45degree bevel gears at the Z
ballscrew and gives an a total
ratio of 4:1. It seems that the bevel gears are the problem as they
have some slop between
meshing the teeth. If I reduce the air assist on the table to force
the ballscrew to have some
pre-load or tension, then the stepper has to work harder and my top
speed goes down.

I've tried a first attempt at shimming the bevel gears to force them
together to mesh tighter, but don't
really like this solution. Any ideas what I can do? This seems like a
bad design choice to use non-helical
gears here.

Thanks for any ideas,
Lee