I am a new owner of a small metal lathe and milling machine. My first
milling project will be some half inch hinges for a Christmas present.

Materials will be brass for the hinge and drill rod for the pin. I am
reverse engineering a hinge that has a 5/64 inch diameter pin.

My third edition American Machinists Handbook states that for a press fit
the pin should be 0.0075 to 0.001 inch larger than the hole. For a running
fit the hole needs to be 0.0005 to 0.001 inch larger than the pin.

I plan on using an arbor press to install the pin in the hinge.

By going with wire gage drill rod and chucking reamers I have settled on the
following:

The hinge pin would be #46 drill rod, 0.079 in. diameter.
The press fit hole will be either a 5/64 bit (0.0781) or a #47 ream
(0.0785).
The loose fit hole will be a #46 ream (0.0810) sizing a hole left by a
5/64th bit.

(dimensions taken from travers catalog)

Here are my questions:

1. Which is easier to work with, Oil or Water Hardened drill rod?

2. Will I be able to use a cutoff tool on my lathe to cut the pins to
length?

3. Are my choices for drill/ream/rod sane?

4. Is there something obvious I should know before starting on this?

Thanks for your help.


Either type of drill rod should be fine, and will be about as easy to work.
But, you are not going to be doing any appreciable work on the drill rod - just
cutting to length.

I wouldn't worry about cutting to length. You'll be pressing it into the hinge
barrels, and I would start with an over long piece, with a slight chamfer on
the end to be inserted. Press in until flush, then
cut/grind/file/mill/sand/hone off the protruding end.

Using a cutoff tool on such a small piece of rod isn't really necessary. In
any case, you'll end up with a small "tit" which you'll have to remove by hand
anyway.

Whichever rod you use, it will be harder in its annealed state (as sold) than
the brass, and won't need hardening.

Your drill rod dimension doesn't make sense. #46 drill rod is .0810, same as
the #46 drill or reamer size.

You can get reamers in any of the fractional or number sizes, and in special
decimal sizes every .0005".

A running fit is for bearings - you don't have to worry about that. I'd
probably use the #46 reamer for both sets of holes, and, if the pin tended to
work loose, put some punch or chisel marks towards one end and then re-insert.
If you don't like that, use an .0005" undersize reamer for both sets and see
how it fits. If it doesn't move easily enough, open one leaf up to the #46.

I've thought about making hinges myself. Let us know how it turns out.

John Martin