Re: [CAD_CAM_EDM_DRO] Re: doubling resolution strategy # 2

>
> P.S. It's nice to see someone actually trying to find the "real world
> accuracy of the machine. So many just "trust" or "assume", based on
> resolution...

I did this with mine. I set up a milled bar as perfectly parallel to the X axis
as possible, as a 'ruler' to lay the gage blocks against. It had a right angle
piece at one end, to rest the first block against. I used it both to measure
absolute error at one inch intervals and to measure backlash at different
positions. I found that my high-precision ballscrews were so accurate that
it was not beneficial to set up the corrector cams. These ballscrews were
out of an Excellon PC board drilling machine. The X screw has a travel of
about 30 inches, but I only have enough gage blocks to do about one foot
so far. Over that foot, the error was definitely less than .001". It was hard
to read it much finer than that due to several different effects all causing
some repeatability problems.

> P.P.S. You could also design some "parts" which can be tested for
> size/geometry/location. Based on the metrology of the parts, you will
> know what your machine can, and can't do. The trick here is in the
> design of suitable "test" parts... But really, if the machine makes
> the parts YOU need to make, to the tolerances that YOU are capable of
> checking, isn't that enough?

This is much harder, as the cutting forces cause all sorts of deflections
in the cutting tool, the workpiece, and the machine itself. Also, when cutting,
there are thermal effects in the workpiece, and the machine - especially
in the spindle housing. Using the wrong tool in the wrong place can
easily cause tool deflections that swamp any other machine inaccuracy.

Jon