Re: Looking for a decent milling tutorial

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "bll_nlsn" <donkey57@...> wrote:

>
>
> There have already been some very good replies to your questions. I
> will add a little more info.

While fully concurring with the previous responses, I'll chip in as well:

I've had very good success holding material to a sacrificial plate
with super glue (cyano-acetate). I recommend the gel type which is
more forgiving of less than perfectly smooth, flat stock. Lay down a
thin bead around the periphery of your cut line and clamp down firmly
to set.

Release the bond by heating with a torch. I use one of those
miniature, refillable butane types. Takes maybe 2 minutes through an
1/8" plate. Clean off the residue with acetone.

I also have a supply of machinable foam I rescued from being discarded
by a commercial shop. This stuff was used to test run DNC programs at
high speed. Not used much anymore as CAM software has become more
reliable. Makes an excellent sacrificial plate when you have room to
clamp. McMaster-Carr carries it, but it's pretty expensive. Some
commercial shop in your area may have some they'd like to get rid of.

Another idea is machinable wax, also available from McMaster. This can
be machined to make semi-permanent fixtures like backing plates. Was
also used for rapid prototyping and testing DNC programs. Reusable --
it can be melted in a tin cup on a hotplate and re-cast as needed.
Also used for making thin walled parts or features. Say you need a
very thin bushing: drill, bore, ream the finished ID. Fill with molten
wax, machine the OD. The wax core keeps the wall from tearing or
crushing. Leave the wax in to press the bushing into your assembly,
then melt it out. I've make stainless steel bushings with walls as
thin as a few thousandths inch this way. (Just for fun, try a super
thin walled, oddly shaped, shot glass, impress your friends.)

There is a class of low melting temperature metals called Cerro Alloys
that can be used in the same way.

Holding parts can be one of most challenging aspects of machining.
Newer hands are often surprised by how much time we spend making jigs
and fixtures. But, there's no way around it; if you can't hold the
part properly, it's impossible to machine it properly. Years of
experience seeing hundreds of clever techniques for holding things is
what makes an old hand.

If you have a sketch you'd like to post, I'm sure many of us would be
happy to advise how we would go about it. I think this would benefit
everyone. Even after 30+ years, I'm still learning new tricks.

regards,

DC