Re: Rack Gear, and Pinion suggestions ?

>--- In CAD_CAM_EDM_DRO@yahoogroups.com, "eightwgt2003"
><eightwgt@a...> wrote:
> I am building a 4X8 router with a 10" gantry height. I purchased
> plans from Machine Tool Camp, but have decided to use the plans
>more
> as a guide and improve the machines accuracy. I am trying to get
> TRUE .01 (1/100) accuracy out of the machine at a reasonable cost.
>I
> am looking for suggestions on rack systems / manufacturers.
>Backlash
> is a concern as you all know.... I looked at ball screws but trying
> to get away cheaper since I want to drive the unit from both sides
> with a jack shaft, and timing belts to drive each pinion gear.....
> ANY help and suggestions are appreciated. By the way - I am
>building
> the frame from Minitec extruded aluminium, and bolting machined
> aluminium tool plate (1")to it to close the tolerances as far as
>the
> straightness..... linear guides will be continous supported 3/4"
> shafts, with open pillow blocks on all 3 axis.
> Thank you
>
> Tom M

Tom, As you have said backlash will be a problem.
One of my customers has 4 laser cutters that work on twin precision
rack and pinions guaranteed to 0.01mm but you don't want to know how
much these cost <bg>

One way to reduce the backlash is to use as wide a gear and rack as
possible and then split the gear. Secure one half to the drive shaft
and then spring load the other half slightly out of mesh. This then
takes up any play in the rack but can compensate for any unevenness
that you have.
See http://www.sdp-si.com/D241/PDF/D241p036.pdf
for a pic of the setup.

John S.