A lot of helpful hints in your post, Roy, thanks. This is the type
of info one would pick up as an apprentice in a machine shop, I
guess. I'm looking around for a new steel collet for use as my
standard.
Meanwhile, I'm roughing out blanks for some 3C collets in steel per
the Exactus articles. I annealed the steel from the rod in a large
shock absorber and can now machine it -- it seemed very hard prior to
annealing in my fireplace; there is a good side to the cool spring
we're having!
Regards, John
--- In 7x12minilathe@..., "roylowenthal"
<roylowenthal@y...> wrote:
My choice for a "standard" collet would be a pristine steel one,
from one of the suppliers who states accuracy. I'd use it to hold
an
accurately ground test rod - dowel pins are good. I've had
horrible
results with drill blanks not being straight!
I always use indicators on stationary parts; without the cute
little roller point, I don't indicate parts while they're moving.
For a runout check, I'd manually rotate the test piece to 4
perpendicular points. If a tiny bit of reverse rotation causes
large
indicated runout change, it's a symptom of dragging the indicator.
Back rotate or not, just be consistent on all measurements.
It's also better to keep oil away from indicators - sooner or
later, some gets inside. It doesn't take much oil to make an
indicator really sticky & unusable (think millidrops!)
Leaving things .001" or so oversize allows room for
filing/polishing for final finish. When I'm trying to make a new
surface concentric with or blended into an existing one, I use the
4-
jaw. When I've used collets for that sort of thing, they still
needed indicating & gentle persuasion with a small rawhide mallet.
Roy
--- In 7x12minilathe@..., "John" <moran03@e...> wrote:
The collet is a new SB, sk-polishing offers these frequently on
eBay
and I took advantage when one didn't seem to draw many bids. I
have
accepted it as a standard in testing my collet chuck, at least so
far...
Your comment on working to tenths is very interesting. Having no
experience or training in machining I've been developing my own
methods on an ad hoc basis. I've run into the problem you
mentioned
of "noise" on the DTI due to surface finish; my crude solution
has
been to use fine carbide paper to polish the surface a bit prior
to
taking the reading. I then wipe the surface with a paper towel
and
add a little oil. My measuring technique is to run the lathe at
its
lowest speed, about 12 rpm, and watch the DTI. The needle is
still
a
little shivery but watching several cycles allows me to get a
reading
by averaging the maximum and minimum readings. I am open to any
improvements in technique since I am very much a beginner at this.
Your point on accepting a couple of mils of runout is one I have
slowly arrived at in using the 3 jaw. Lately, I try to leave the
diameter on the large side if a part will need to be removed and
re-
installed in the chuck, going to the finish size as the last step
when possible.
Thanks for the info.
John
