Re: Re: Scratch-built CNC mill

>From: "Ian W. Wright" <ian@...>

>The question really should be - why *do* people use glass scales. Close
>contacts with a company which made precision measuring products taught
>me that the material which machine scales are made from should match
>either that of the machine itself or the material being processed. In
>this way, its not necessary to take any account of changes in
>temperature. That is - a steel scale on a steel machine will remain
>proportional at all temperatures. If you are working hard on a large
>metal part it gets hot and will consequently expand, so, logically, if
>you are relying on a scale which does not expand as much or is in a
>position where it is not affected by the heat of the work, the work will
>finish up undersize when it cools down. opinions anyone??
>

I have seen reports that where very high accuracy is required the machine
is always left switched on. It is in a temperature controlled environment
and most importantly the coolant is supplied in a flood at a carefully
regulated, above ambient temperature. The machine is calibrated at that
temperature. Not really practical in the home workshop but then how many of
us have machines capable of repeatable performance at those levels anyway?

Randolph Lee has pointed the way to the Heidenhain web site. If you would
like to see a metal tape measurement system look at
http://www.renishaw.com/encoder and have a rummage around. I have to put
that plug in because I work for Renishaw. As yet though I don't have any
readout out systems in my workshop. Would be useful though if only to
convert between metric and imperial.

regards
Bill Phillips