Re: [CAD_CAM_EDM_DRO] Ideas needed: techniques to reduce Z axis slop:

Lee Studley wrote:

>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.
>
>

I really don't think there is much of a solution to this. This is part
of the reason why I
made the quill my Z axis. The only real solution I can think of
requires throwing away
the bevel gears, and rigging a pulley somehow to connect a motor
(probably outside the
knee) to the screw on the inside. You could cut a hole in the side of
the knee to bring the
belt out. Or, you could put the nut in the knee, and put the bearings
for the screw on
the bottom, where the nut goes on a Series-I manual machine. Then, the
motor and drive
could be in a box on the base casting. I'm not familiar enough with the
Series-II to
know which of these would work better.

Jon