Re: Vertex Rotary Table Backlash

>--- In CAD_CAM_EDM_DRO@yahoogroups.com, "alex" <telecomt@t...> wrote:
> >
> > Because you need the high worm ratio to prevent cutting forces
> > driving the table. Try turning a 10:1 gearbox the wrong way, it's
>not
> > that hard and to get a high enough ratio that would prevent run
>back
> > on chain or belt would be an enormous ratio and physically
>impossible
> > to fit in.
>
> Thank you for the explanation, but for this, brake can be invoked!
>

Not if you are using the table for continious cutting. A brake is Ok
for plain indexing if you can rely on the braking action not to jog
the spindle.
If you are continious cutting then the cutting forces can ans will
move the table.
The very first indexing head I built was made from an old headstock
off a lathe with a big type 42 stepper of 1100 oz/in driving the
spindle thru an 8:1 reduction arrived at by running a 10 T timing
sprocket against an 80 T sprocket. This was heavy duty stuff, 3/8"
pitch by 1" wide belt.
First job was milling a face cam on the front of a 2" diameter bar
with a 1/2" cutter. As the cutter started getting into the cut which
was not excessive you could hear the motor loosing steps.
I managed to do the job by just taking very light cuts and once
finished promptly scrapped the head and went onto converting a big
dividing head.
See pic near the botton of this page.
http://www.jeffree.co.uk/DivisionMaster/Examples.html

John S.