Re: [CAD_CAM_EDM_DRO] doubling resolution strategy # 2

In a message dated 03/09/2001 12:22:14 AM Hawaiian Standard Time,
Ian@... writes:

> This is something I have been fighting with for the last couple of days. How
> DO you check the accuracy of either cnc or dro systems to the accuracies we
> seem to be capable of?
> Then I commanded a move of 1.000mm - the dial
> moved to 0.900mm exactly!! Sent it back to 0 - it now read 0, sent it to
> 1.000mm, it read 0.9mm - damn! This was getting frustrating. So, I decided
> I'd try the digital vernier again and fixed one leg to the end block and
> clamped the other to the carriage - now that must be accurate! Sent the
> carriage to 100.000mm - the vernier now read 99.75mm - back to 0 - it read
> 0. Sent it to 50.000mm - it read 49.68! still perfectly repeatable back and
> forth. This is silly.
> Ian
> --
> Ian W. Wright
>

Ian,

I mounted a 1" travel dial indicator to my machine and tested it it for
backlash first. Try approaching a given dimension from both direction. For
example, go to .500" from zero. set the dial to .500". then go to .750 and
see what it is. Go back to .500 (so that you approach from the opposite end)
and see what it is. Go to .250 etc etc. You will see a pattern that reveals
the problem. Either backlash in the nuts or improper bearing preloads etc. If
you have two dials, you can also watch the relationship of the screw's axial
movement to the table.

Now assuming you know how much lash you have, then you can do a linearity
check with gage blocks or micrometer standards. A good digital caliper
mounted as you did would be OK for non critical set ups....

Peter
THRd, Inc.



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