got a 12" 123 starrett. all thumbscrews were rusted. cosistently .002
inside scale way off.
ground a custom screwdriver bit to fit the adjusting screws(i think
theyre gunsmithing screws).
soaked thumbscrews in crc and wire-wheeled off rust with dremel and a
brass wire brush.
this also removed all bluing.
heated screws cherry red and quenched in peanut oil.
this restored bluing to factory.
knurling on the now harder screws feels like it 'bites' better.
cleaned with micro-teflon spray.(the suspension cleans everything
leaving a microscopic teflon film)
calibrated with gage block set.
found out that .2935 is the actual width of jaw prongs to be added for
inside measurements. not the .300 starrett says.
used a .1005 block, put in jaws and adjusted 'inside' scale to read
Verified with micrometer.
They look and work brand new. incredibly so. The new bluing is beyond
tenacious, unlike trying to blue a zinc plated nut.
used micrometer to set jaws .0005" open and checked light gap.
theyre flat to .0005 at most. but i'd love to get the jaws on an
optical flat and see how flat they are in microinches.
i really really like my gage blocks now. and grade3 is great. they say
longitudinal stability is now .000001"*L per decade. cool.
and i always thought bluing was a chemical process. (maybe for
gunsmiths, but not for watchmakers):-)
18 years ago