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From: patv@...

I'm into model railroading and I've been trying to make HO scale parts
using automated techniques. Unlike most folks, I'm not as concerned about
power as I am about the ability to machine details. For example, a 1"
dome representing a rivet in HO scale is 0.0115" in diameter and 0.0057"
high. Spacing in between these may go as close as a scale 1.5" centers or
only 0.0057" gap between domes. As you can see, this would mean I need
some very tiny end and ball mills.

Interestingly, I have some of the same needs in my clockmaking work. The
beading on clock bezels is the same sort of thing, and the "beads" almost
touch. I was planning to make a special form cutter, where the cutter
would have an internal radius to machine the raised "hump" It would be
easier to form the cutter if it was a single flute, and with soft metals
(brass in my case) it should work.

You could also machine a negative form, making the rivit heads with a ball
mill, using it as a form for a lost wax pattern. The old clockmakers had
special form knurls, not only for beads, but for crosshatching, acanthus
leaves, ad infinitum, which were rolled onto a soft cast blank.

David M. Munro

From: "David M. Munro" <munro@...>

*** snip ***

Interestingly, I have some of the same needs in my clockmaking work.

The

beading on clock bezels is the same sort of thing, and the "beads"

almost

touch. I was planning to make a special form cutter, where the cutter
would have an internal radius to machine the raised "hump" It would be
easier to form the cutter if it was a single flute, and with soft metals
(brass in my case) it should work.

The thought of special cutters has crossed my mind. Unfortunately, I've
never needed one and have no idea of how to make one. Got to hit the ole
books to see if I ever learned anything in that area.

You could also machine a negative form, making the rivit heads with a

ball

mill, using it as a form for a lost wax pattern. The old clockmakers

had

special form knurls, not only for beads, but for crosshatching, acanthus
leaves, ad infinitum, which were rolled onto a soft cast blank.

Actually, I have a small arbor press and punch set with a single axis
table the will emboss rivets into thin sheets of plastic or brass. I've
used it before, but the table is garbage. I need to rebuild it with a
real x-y table to accurately emboss a rivet pattern. Thought about using
a solenoid and two steppers to automate this one, but that's a different
story ;-) The ball mill and reverse pattern does seem to be the best
suggestion so far.

The rivet is only an example of the the relative sizes of the detail I
need. I did think of chemical milling as a possibility, but wanted to see
if there's a CNC solution first.

Pat


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Some years ago I built a microscopic mill for a production plant and I think it might work for you also.

I bought a dental air turbine. It runs at about 400 to 500 thousand RPM (no, I did not get one zero too many). It was not
expensive either if I remember correctly. Do not buy the whole handle or they will charge an arm and a leg, just buy the
replacement turbine and then make a little housing for it so you can mount it in the regular CNC spindle.

Remember to add a drop of oil now and then or an oil mister to the air supply. The plant machined millions of small parts with
the one I built without wearing it out.

Check with dental supply houses. There was a company in the "Home Shop Machinist" that used to sell a turbine mounted in a
little handle that they made but I do not remember their name.

There are all kinds of dental burrs, both carbide and diamond.

Good Luck
Bertho Boman
Vinland Corporation