Re: [CAD_CAM_EDM_DRO] Making leadscrews more accurate

Les Watts wrote:

> > Les wrote:
> > >Rather than XXYZ control the minor pitch variation between the two x
> > >screws is taken out by a simple cam/rotating ballnut.
> > >It's an old victorian trick to make a leadscrew's pitch more
> > >accurate than it was manufactured to.
> >
> > Les,
> >
> > Please tell us more about this! And/Or post links/Refs??

On the Excellon PC board drilling machine, they had a high accuracy
positioning system based on a GE Century-100 control - really old,
thousands of Germanium transistors on one-sided paper-phenolic
PC boards. It used resolvers for feedback. The resolver body was
mounted on bearings, with a spring-loaded arm that followed a cam
about 6" in diameter. The cam was turned by the leadscrew through
a 150:1 reduction gearbox, so that the cam made less than one
revolution for the full linear travel of the leadscrew. The cam was
hand filed (I think) to correct for variations in the leadscrews, which
were already high-accuracy grade. I left this mechanism disconnected
when I re-fitted these axis drives to my Bridgeport. The screws measure
out to better than .0003" / 36" travel, so it seems unnecessary!