Re:

patv@... wrote:

> 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.

These tools are definitely available. Most of the tool catalogs (J&L,
MSC, KBC, etc.) have them
listed under micro end mills. You can use 'corner rounding' end mills
to make the convex rivet head
shape easily, and standard end mills to cut down the surface in
between. I just did a job using
a corner rounding end mill to make a 180 degree rounded 'hill' on a mold
for a friend. If I had
made the corner rounding mill orbit around in a circle of the right
radius, it would have made a
hemispherical bump.

> So, anyone have any experience with this type of work? What process
> do
> the commercial boys use when making their molds? Are they using
> exotic
> techniques? Also, do any of these CAD post processors like DeskProto
> allow
> for programming of cutter geometries, such as conical as opposed to
> simple
> ball and end mill diameters?

Bobcad/CAM can do this, but it is difficult enough that you often figure
out the tool offsets
yourself and then tell the CAM package to follow some pattern in the CAD
drawing with
the specified offset. But, Bobcad/CAM can do at least some of this. It
may be limited
to square and radius end mills, when the radius = 1/2 diameter, that
makes a ball end mill.
But, maybe there's a way to have it do end mills with negative radius,
which is what a
corner rounding mill is. Anyway, we just figured the offset ourselves,
and then had Bobcad
follow the curve at that offset.

Jon