"Cydrome Leader" wrote in message
...
I've been making some parts out of 1/2" aluminum rod which get
turned down
to 0.200 for 3/8" of an inch, and the end chopped off.
...
Is this what anybody else would do? I have no machinist pals to drop
by
and chat about stuff like this with.
If I read you right they are shaped like a thick-brimmed top hat or a
rimmed bushing.
http://image.made-in-china.com/2f0j0...te-Bushing.jpg
I'd do about the same as you except that I rough nearly to size, then
make one or two finish cuts based on measuring the part and advancing
the bit almost half the oversize. This compensates for the wear in my
1965 lathe. If I'm careful I can hit the diameter within 0.0002", over
a short length that varies with shaft deflection.
For the shoulder position, if I didn't have a micrometer carriage stop
I'd face it square and a little long after finishing the diameter,
then locate the facing bit 0.375" from the shoulder with dial calipers
or some handy gauge and face off the end of the 0.200 diameter. I can
usually get within 0.005" with a ruler and magnifier headband.
I locate the cutoff bit from the shoulder with the depth rod end of a
dial caliper. The 4" size is handier for confined spaces, especially
when milling. Rocking the caliper slightly shows whether it is
contacting the shoulder or the cutoff bit. It's probably good to
0.001" but I may cut it long and face smoothly to length with the part
reversed in the chuck.
I had a company-property Sherline lathe and mill to play with for a
while. After using a bigger lathe it seems incredibly limiting. My 10"
lathe will do the same tiny work like threading custom #0-80 screws. I
kept my first small lathe after buying it because the small one spins
much faster and so is better for drilling small deep holes, and
polishing.
I grind my HSS bits about like this:
http://www.iowa-industrial.com/Trist...image-No-2.jpg
but with a more acute angle at the tip so they both turn and face
cleanly. The shank has to be angled in the tool post, easy with a
Multifix or old-style lantern toolpost, harder with a square or
turret. If the junction of the diameter and face matter I grind the
point sharp or rounded to match, or use a triangular insert.
jsw