"awh" wrote in message
k.net...
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?

Both of them will be more difficult to machine than mild steel, but you're
likely to notice little difference between them until you have a little
experience machining. Because water hardening is only carbon steel, it
tends to be more economical than oil hardening, which is an alloy tool
steel.

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

That is more a function of your lathe than anything. Parting is very
difficult because parting is a rather demanding operation, especially if
you're using commercial parting tools,which can be rather broad. If you
have a very small machine, I would suggest to you that you hand grind a
narrow parting tool, something in the neighborhood of 3/64" wide, with
proper side, front, and back clearance, and with a chip breaker type of rake
on top. You want about 8° to 10° angle at the cutting tip, with the chip
breaker a fairly large radius that permits the chips to flow towards the
rear of the tool without interruption. That style of parting tool lends
itself extremely well to parting small, tough material. Use a slow feed (by
hand in this instance), reasonable speed, and lubricate well, using a sulfur
based cutting oil. They stink, but they work well. With a tool this
small, if you get in trouble, the tool will break instead of doing damage to
your lathe, a very negative experience I had when I was a boy and learning
the machinist trade. I ruined the ½"-20 spindle on my little Craftsman
lathe.

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

Actually, yes. For a hinge pin you will start with material that is
relatively round, straight, has a nice finish, and is tough. You will have
no need to heat treat the material for a hinge pin, which I would recommend
you also do not do. Once you heat treat long, slender items, the chance of
them staying straight are not good.

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

Only that drills do not make very good holes. If you don't own any reamers
and think you'd rather not invest in them, a rather smart idea for *******
sized reamers that may never be used again, you should practice drilling
holes in steps. Good practice in the shop dictates that you center drill
(or spot drill with a spotting drill), drill undersize, then drill to size.
That works very well in general, but in brass it can be a bad experience due
to the ability of brass to "hog in". That means that when you open up the
hole, the drill will grab and self feed. That can lead to ripped up hands
if you're holding things that way, broken drills, and damaged parts. If
you're familiar with how to reduce rake angle on drills, all you have to do
is reduce the rake angle to 0° and the drill won't grab, though. You can
also drill with your drill as ground, but you have to use a little drag on
the spindle of your mill, and must also be able to "feel" what is happening.
Again, without some experience, this may be a bit beyond your ability, but
it's not something that you can't learn by trying. There's really no better
way to understand things like this than to experience them.

One other thing to keep in mind. When you remove the bulk of material as
you're making the hinges, the parts are most likely to not stay flat.
Don't make the mistake of drilling your holes first, otherwise the parts are
unlikely to accept the pin. Rough the parts completely, then go back and
take finishing cuts. You could probably drill the holes after the roughing
operation and get by, but drilling them last might be your best choice. That
means that you will be drilling from boss to boss, so in this instance the
reamer may be a better choice because it has a better chance of achieving
holes that are in alignment. Play with some scrap stock at first if you
have that luxury. Try to make your mistakes on something that has little to
no value to you.

Thanks for your help.

My pleasure.

Harold