"Jeff Wisnia" wrote in message
...
snip---
My inquiring mind want's to know....

In general, what sort of temperature differentials are acceptable when
working to those tolerances on measurements of a few inches or so with
common metals?

ie, do you have to worry much about the body temperature of your hands
affecting parts or instruments.,

Jeff

The .0001" work I used to do was done in a shop with no temperature
controls, but keep in mind that the work was very small, so the temperature
differential was less of a concern than it would be on larger items. Good
sense is a part of success-----allowing for expansion when necessary, or
cooling parts and instruments to an acceptable level.

On larger items, temperature can be a serious factor. Case in point: I ran
an order of spacers, quantity of 630, for the main landing gear on a C-130.
The spacer was about 6-3/4" diameter as I recall. I still have one
somewhere in storage, but don't have a clue where it is. It was made from
7075-T6 aluminum tubing, and had a 1" corner radius that went into a 7
degree taper. The part was turned on a lathe with a hydraulic duplicator.
There was a straight portion of the spacer that was held to +/1 .001", about
an inch long. For finishing cuts, the properly roughed parts were
introduced to soft jaws that were warm from heat from the headstock, so the
parts expanded as they were machined, in spite of a small supply of coolant
being applied. In order to end up with a straight turn, the template was
dialed in with a slight angle, about a half thou as I recall, so the finish
machined part was straight. The angled template compensated for the ever
growing part. It goes without saying that the timing in running the parts
was critical----otherwise the expansion wasn't in lock step with the
template setting.

Typical grinding tolerance was usually .0002", which we accomplished in the
shop with no particular care aside from general shop methods. Temperature
swings in precision grinding are generally not very wide, due to almost all
operations being run under flood cooling. The huge volume of coolant in the
machines tends to keep the temperature stable.

As for the ring gauges with the .000020" tolerance, the parts were inspected
for size at the machine by a second (unbiased) party, then were required to
sit in the gauge lab for 24 hours before being certified. Temperature and
humidity are both important. The gauge lab was kept at 68 F as I recall,
but I have no clue of the acceptable level of humidity.

Bear in mind that our normal work did not require holding such tight
tolerances. The set of ring gauges was an anomaly, due to an immediate need
that could not be met commercially. The rings were sized on a standard,
manual, Sunnen hone. The hone is more than capable, but it requires
skillful application.

Harold