Re: Ideas needed: techniques to reduce Z axis slop:

Hi Jon,
I like the idea to modify my quill for a ballscrew at some point. I
also like the belt idea, but it will be hard to do, there's a casting
around the knee ballscrew bevel gear, so it would be a major machine
mod. I'm going to scope it out today to see how I might do that. Also
I came up with a thrust bearing idea to push the bevels together with
an adjustable spring tension that will be easy to implement, but as
the bevels wear it may not last? I bet it will be ok for many years
of my usage...

-Lee

--- In CAD_CAM_EDM_DRO@yahoogroups.com, Jon Elson <elson@p...> wrote:
>
>
> 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