Re: part holding

--- In CAD_CAM_EDM_DRO@yahoogroups.com, Tom Hubin <thubin@e...> wrote:

> Hello Rick,
>
> > The hardest part about cnc is not the electronics, the servos, the
> > ballscrews. The hardest part is holding down the friggen part!
> <snip>
> > How do you guys hold down a part when
> > you want to machine 5 surfaces on it?
>
> I make fixtures for the parts. I use dowel pins (usually 1/8 inch
> diameter) to securely and accurately locate the parts on the

fixture. I

> can remove parts, inspect, reorient, and replace within a fraction

of

> 0.001 inch.

Hey Tom, thanks for the reply.

How do you hold down a part with dowel pins while taking a 0.125" cut
with a 1/2" endmill? Or do you mean you use bolts or screws into
your fixture to hold the part to it and the dowel pins are just for
alignment?

Things I have done in the past are: Machine part out of much larger
stock which is held down to the mill table with clamps. Trick is to
not machine all the way through, leaving perhaps .025 metal. Then
take part to bandsaw, cut it out, flip it over and flycut the back to
the final thickness. This wastes a lot of metal though...

Anyway, I think I know what you were talking about with the fixture
idea...I have done similar things. I normally would have run the
program in air just to make sure things were going to be ok, but in
this case I thought I could just squeak by the clamps with a few thou
to spare. :-)

Rick