16 years ago
(~35 year old AMT 10" Bench) to something with more precision -- since I'm
regularly drilling #70's for PC board holes and have a future need to go up
to #90 or so -- I measured it's runout over the weekend. Runout was a
little less than +-0.0015" or just under .003" total. I was advised that
it's about as good as could be expected, but I felt that I needed more so I
said, "Hey, I've got an old Dremel drill press stand that I've used for
years. Maybe it's better."
One part of the measurement is a little unorthodox -- I had to measure it
with the unit running. Okay, I was using the Dremel benchtop speed control
set to absolute minimum and I don't think it was running more than about
50-60 RPM [visually about 1 second around], but since it's a direct drive
and the motor is enclosed in the hand tool's housing, it's the only way to
get it to go around without actually putting a finger on it and turning it
which also pushes the shaft sideways.
But the results were no better than the bigger unit. I watched the needle
on the dial indicator wiggle between two readings that were exactly .003"
apart and the rate of motion was similar to what I saw as the rotational
speed of the shaft.
With that much runout, I'll never be able to drill down in the #80's with
carbide bits -- except maybe for making pinholes in .002 brass sheet [which
is one use I'm going to have].
But the bottom line is that I'm going to need something considerably better.
I guess I'll watch eBay for a week or two to see if anything turns up and if
it doesn't I'll probably have to start pitching quarters in the jar to save
up for the new unit.
Thanks for all the suggestions.