I designed a couple of parts that I now need to get CNC machined
(mill). I have sent many parts out for laser cutting, but this would
be my first to a CNC shop. As with the laser cut projects, I did the
drawings in Alibre Professional, and now I need to familiarize myself
with the next step for CNC work. I have a couple of small shops that
I am going to approach to run the parts for me, and of course I am

going to ask them how they would proceed... but I would like to ask
the group here what the normal way things happen. Please keep in
mind, I plan to purchase some sort of entry level CNC mill in the next
year or so. Something like a Tormach, or if I could find a used
machine, the Sharp 2412 has been suggested to me... anyways, this post
is not meant to generate talk about the actual machines, more the
methods.

One of my major CNC prep questions is HOW ARE THE PARTS HELD. Both of
these parts are to be milled out of rectangular bar stock, and with
these parts, the finished product will not leave much to hold on to...
hence my concern.

I am trying to incorporate mounting points in the product design, to
allow these parts to be fastened to a jig, but it seems this is a two
step process...

I am picturing in my mind's eye how this would progress thru the
steps.

First I would have to give them (or design for them to machine) a jig
(called jig B) that would hold the parts.

The only way I can envision the next step is for the shop to hold the
raw material (in this case a 4" wide x .750 thick aluminum bar stock)
either on a basic jig (called jig A) on the mill table, or in a simple
mill vice, then run a first program to drill the fixturing holes that
I have designed into the part for second step fixturing in JIG B.
They would then have to remove the part from JIG A and install in jig
B, and run the rest of the program. Is this plausable?

My Next concern would be the something that only the shop I choose
will answer 100%, but could I expect to give them the DFX file and
they then can convert it over to talk to their machines?

Then, how does one decide what tooling to use? We are talking about
smaller shops without the budget for the latest/greatest software...
so does something like MACH3 or the other CAM software pick the tool
sizes? Or does the machine programmer look at the print and say... OK,
I'll use a .250 end mill for here, and a .750 for there, etc??

I suppose this leads to another question... is it prudent for the
person drawing the files to try and use radius' thruout the part that
coincides with common sizes of tooling? I mean if I need a radius on
a part, and the shape is not a critical design element, then Pick
something simple like a .250 radius? Is that just good design work..
meaning everyone in the trade already knows to do that?

thanks alot, I appreciate any helpful comments!