Yes Joe, it's amazing. The center of the job shop when I was
active was the Bridgeport and most average machinists could
only hold a tolerance of a mil or two on an old mill. A really
good machinist could work down to the tenths with a well
maintained machine but at that level your getting into an area
where temperature becomes a factor in dimensioning, especially
as the part you're working on grows in size.
The CNC mills, lathes and machining centers of today can hold
those close tolerances in a controlled environment, typically
68°F or 20°C if using NIST as the standard. I'm not a CNC
programmer but I believe my nephew who is, has told me there
is temperature compensation built into the programs now. This
would account for the reason they can hold such tight
tolerance's even when there are deviations in shop temperature.
Curt is more qualified to comment on that than I am.
Denny Graham
Sandwich, IL
