On 2009-07-25, Tim Wescott wrote:
I'm going to make a wire-bending fixture for putting fairly small-radius
bends into 1/8" music wire*. I have some 1/8" oil hardening drill rod
and a slightly undersized 1/8" reamer designed for installing dowel pins
in tooling. I also have some 1-1/4" round bar, made of mystery steel but
there's a good chance that it'll harden at least a bit if encouraged.
You know of dowel pins already -- so why not get some. 1/8"
dowel pins are quite inexpensive, and a *lot* harder than you could get
the drill rod to be without it being too brittle.
As for the mystery steel -- I think that it is as likely as not
to be low carbon enough so you won't get *any* appreciable hardening
with it. But why would you need that? You want it tough, to hold the
dowel pins, not hard, because it is not a wear surface in this
application.
So I'm planning on putting a couple of pins made out of the drill rod
into the end of a bar, and bending the music wire around the pins. I'm
_assuming_ that if I don't harden the drill rod that it'll bend, although
I'm in a hurry so I'm going to test that assumption by trying to use the
tool.
And music wire is hard enough so it will dent the drill rod,
likely even if you've hardened it before use.
After I bend up my first attempt at a fixture I'll want to do it up
right. It seems like I should just be able to heat up my whole assembly
to a dull red then chuck the thing into a bucket of water -- does this
sound correct?
Water is too extreme a chill for oil-hardening drill rod. Cut
the rod to length and bevel the ends (assuming that you don't get dowel
pins), then wrap them and some paper in some stainless steel foil wrap,
crimp it closed and pack as tight as possible around the pins to exclude
as much air as possible, then heat that to your red heat. The foil
keeps out any air which is not already there, and the paper burns up the
oxygen which is already inside.
Once you reach the red heat, cut off the end of the stainless
steel wrap and let it fall into a container of oil -- engine oil will do
if you don't have anything better. This will quench it at the proper
rate. You might have a flash of flame from the vapor at the top of the
oil's surface, but it will go out very quickly. (Do it outside anyway to
be safe.)
I have some pottery clay lying around so I'll probably
paint the pins with clay & charcoal in an attempt to protect them from
decarburization.
The pins are what you need *hard*, and by protecting them from
the oil you will not get nearly as much hardening as you want.
When I fish it out of the bucket should I try tempering
it? If so, how, and how much?
Forget about hardening the body of the fixture, and get dowel
pins which are already very hard and you won't have to worry about this.
But if you harden the drill rod -- read up on the tempering
temperatures of the rod which you have and aim for just a little less
hard than full hard. At a guess, something like 150 F to 200 F for
perhaps a half hour (these are quite small, so the hour per inch of
thickness need not apply).
But I would go for the dowel pins, not the drill rod. (I've got
both on hand.)
The heat-generating tools I have available are pretty much a propane
torch and an O-A cutting torch. The temperature measurement tools I have
are my own somewhat color blind eyes.
Do the heating in the shade so you have a better chance of
seeing the red. Or -- you could test them with a magnet. When they are
no longer attracted to the magnet, they are ready to quench.
* Music wire is moderately high carbon -- 0.7 to 0.9%, and drawn in a way
that work-hardens it nicely. It's soft enough that you can cut it with
diagonal cutters successfully, but hard enough that you'd better hide the
cutters from their rightful owner when you're done.
I'm not sure that 1/8" music wire will take the kind of bends
which you would get from 1/8" drill rod or dowel pins. Normally for
cutting music wire I would suggest the Starrett carbide faced compound
leverage nippers -- but I think that 1/8" music wire may be a bit too
much for them.
Good Luck,
DoN.
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