Re: [CAD_CAM_EDM_DRO] Re: measuring scales and thermal compensation

In a message dated 3/17/00 11:34:17 PM Hawaiian Standard Time,
Ian@... writes:

<< So, make the scale out of the same stuff as the
bulk of the machine, and they both change length by the same amount.

Ian >>


If you are cutting a long piece of 6061-T6 and your linear encoder scale
is steel and if your coolant is not keeping the part cool, there would be a
large difference in measured and actual size.

Years ago, I worked in a large ship yard. When they machined the tapered
bore of large props, they would start machining around 2 or 3 o'clock in the
morning. Since these props often had bores up to 30+", they were turned very
slowly. To bore the 24 inch depth (these were verticle lathes with 20+ foot
diameter faceplate/chucks) would take many hours. By 6 am, the props were
heated by the cutting action to the point where they were no longer workable.
They were allowed to cool till the next morning. This would go on till the
bore was cut close enough for the bluing process to begin.

I guess the moral of the story is, the parts should be checked carefully
for high temps if they are large. If shrinkage/expansion can be predicted and
compensated for, that's the next best thing. Otherwise, use coolant to help
equalize machine and part temps.

Peter
THRD, Inc.