"Lloyd E. Sponenburgh" wrote:

"Pete C." fired this volley in news:4dd2914a$0$10550
:

Most people use a dial indicator and map the screw an inch at a time.


Not hardly, Pete. I've watched that procedure before on big VMCs. You
want not only "localized" errors, but cumulative errors to be mapped.

My reference was to people doing CNC retrofits, not big commercial
machines. Whe we replaced ball screws on the big machines the new ball
screws came with a pitch error table to enter into the control.

Also, measuring an inch at a time does not "localize" errors, you map
continuously from one end to the other and unless you are quite sloppy,
you introduce no cumulative error into that mapping.


As Ed stated below, the Japanese techs were using laser devices. The could
map a 6' travel to half a tenth, cumulative, easily. (I'm betting it was
better than that)

Yep, the ball screws for real machines are laser mapped. You can
probably buy your ball screws mapped with a pitch error table included
for an extra charge.