On Fri, 24 Feb 2012 18:00:58 -0500, wrote:

On 24 Feb 2012 05:31:07 GMT, "DoN. Nichols"
wrote:

On 2012-02-24, Karl Townsend wrote:
I need to make a pin .25" long by .096" diameter with a 0.109 by 0.117
head. It needs to be hard so I'll make it out of a 7/64 drill bit, the
size of the head.

What's a clever way to hold this in the lathe? it would be hard to
make soft jaws go down this small. I'm thinking some sort of
collapsible bushing that I'd drill.

Can you use 5C collets? If so, consider getting an "emergency"
collet, soft, which can be drilled/bored to size.

Or -- if you have a small enough lathe with a Watchmaker's
spindle, you should be able to find a WW series collet of just the right
size. For the 0.109 (if that is the diameter), a #27 or #28 collet
(they are marked in tenths of mm). For the 0.117 (if *that* is the
diameter, you would need a #30 likely, or perhaps a #29. (It calculates
out as 2.9718mm FWIW.

The WW collets are one of my reasons for holding on to both my
Unimat SL-1000 (with the watchmaker's spindle), and the Taig (with a
similar but less versatile spindle).

Good Luck,
DoN.
Mabee something like a pin vise?

If this is a onesie job, and if there are some standard collets
available, the way I do these things is to wrap steel or copper wire
aound the shank until it fits in a standard collet. You can only use a
single layer, of course.

Otherwise, I turn a sub-collet from anything available and split it
down one side. I've tried splitting them part-way down, with two or
four slits, but the end result doesn't seem to be any better.

Someone mentioned that the shanks of drill bits are soft. That's quite
accurate. Also, they aren't any specific dimension. They're smaller
than the nominal diameter of the bit. Sometimes, they aren't very
round, either.

Oil-hardening drill rod is the ideal material. But you could also make
them from mustic wire. It's going to be quite hard, but it's
plain-carbon steel, so you can anneal it over a kitchen range or
(carefully) with a torch. Then it's easy to heat-treat, heating
quickly and quenching in oil (it's so small that there's no need for
water). Just don't soak it at heat or it will be brittle as hell, from
coarsening of the grain, and you'll de-carb the part. Then temper at
350 - 425 F in a kitchen oven, for an hour or so, to get maximum
strength.

--
Ed Huntress