Re: [CAD_CAM_EDM_DRO] Making leadscrews more accurate

Hi Les,

This is the system used by the highest grade measuring machines. I last saw
it on some Societe Genevois ruling engines in use at James Chesterman's just
before the company closed. They were used there for graduating the highest
grade of scale rules. The procedure was to coat the scale material (usually
stainless steel for scales or glass plates to make 'negatives' to photoetch
slightly lower quality products) with a wax resist and then scratch the
lines through this using a diamond point. Then the scale would have the
lettering applied in a similar way and would go off for etching and,
sometimes, filling of some of the lines.
The other trick of these machines was that they had sloping beds so that the
carriage - on roller bearings - tended to run to one end. It was prevented
from doing so by the nut against which it just rested, always being pushed
uphill by it.

Ian
--
Ian W. Wright
Sheffield UK
www.iw63.freeserve.co.uk

----- Original Message -----
From: "Les Watts" <leswatts@...>
To: <CAD_CAM_EDM_DRO@egroups.com>
Sent: 05 January 2001 18:48
Subject: [CAD_CAM_EDM_DRO] Making leadscrews more accurate


> > 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??
> >
>
>
> Well I have no links because I know of no other one that has done this. I
do
> seem to recall reading about the early machine makers in the 1800's using
> this technique to make leadscrews though. (Maudsley?)
>
> I will be happy to do a little writeup here as I will be grilling
> you guys about an EMC install pretty soon! Let the mechanics
> be as open source as the software.
>
> A ballscrew or other leadscrew has pitch errors that can accumulate to
large
> values over a distance of feet. The preloaded rolled screws I like to use
> are C7 which has
> an e300 of .04mm. In other words .002"/12" pitch error.
> It sometimes is periodic and cancels over length but often does not. There
> is much confusion about cumulative vs non cumulative errors in ballscrew