center pin reamers, homemade

Don Mannino donmannino@worldnet.att.net
Thu, 08 May 1997 11:34:17 -0700


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Greg and List,

If you want to make your own broaches, you can do so out of music
wire. The only one that is tough to find is .050" (or is that 051"?)
but the rest are normal string sizes.

Straighten the wire by pulling it through a hole in a 2x4 (or
whatever). Cut a 5" length and chuck it into a drill. Spin it slowly
with the drill while holding the tip against a belt or disk sander at
an angle to create a sharp point. Smooth and buff the point after it
is sharp.

Then put the wire on a workbench, and with the edge of a large file,
create a 1/2" wide rough area about 4" in from the tip. Apply a lot of
pressure with the edge of the file, and change the angle around so
that the rough area is evenly rough, about like 220 grip sandpaper or
so.

Put the wire into a center pin vice (the little handles that can be
bought from supply houses) or glue it into a wood handle, and voila',
a very nice center pin broach. The rough area must be 1/2" or more
from the handle, so that the bushings pass all the way over the rough
area twice with each reaming.

Since Schaff is set up to make them, I think it's easier to just buy a
set. I'd feel so even more strongly if they paid me something for them
.. . .

My main complaint with using center pins as reamers is that they don't
stay sharp, and each time you make a new one it cuts a little
differently. Hammer centers especially need to be consistent in
friction, and hard steel reamers make this much easier to accomplish,
especially if you are burnishing the bushing to smooth it during the
reaming process.

You can dig up my old article from the October '88 Journal to get the
full description of how to use this type of broach.

Motorized burnishing works pretty well if it's not spinning too fast
as mentioned by Horace, but if this is used to enlarge the hole much
it tends to generate too much heat, and the bushing will sometimes
tighten back up again.

Don Mannino RPT



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