Re: [CAD_CAM_EDM_DRO] New to this Group and new to CNC machine operations!

Hi Tim:
You've asked some really loaded questions here...loaded in the sense
that here's so much to talk about here that I hardly know where to begin.
Moldmaking is a moderately complex undertaking in which you need to know
quite a few details about how the process works, and how to apply it all to
your part so you can achieve the following:
You need the mold cavity to have the right shape to make the part without
spilling any plastic into places it's not supposed to go.
You need a means by which to get the plastic into the mold.
You need a means by which to get the plastic back out of the mold after it
cools.
You need a means by which to control the temperature of the mold.
You need to build it strong enough to work safely under the forces to which
you will subject it when you squirt the plastic in.

Having solved that with your mold design...it's time to start thinking about
how to make the individual mold components.
Many operations are involved, as some parts are quite complex, and they will
invariably consist of some features that can be readily made using CNC
milling as a reasonable approach, and many operations for which milling, CNC
or otherwise, is totally unsuitable.
Many times, the lack of the gear needed to do things in an ideal manner can
be circumvented by cleverness in the mold design...for example, many mold
cavities are normally produced using EDM (electric discharge machining),
but could also be produced by milling and turning, if the mold cavity is
split into several blocks that are then dropped into a milled pocket in
which they can sit and be supported against the many tons of force that
injecting the plastic will create.

One of the key things in moldmaking is knowing where high precision is
absolutely essential to successful and safe mold operation, and where you
can get away with more liberal tolerances.
Some features need to be built dead nuts accurate and like a brick
shithouse, and some matter very little.
Surprisingly, the most liberal tolerances are often on the cavity that will
form the part...deviation from the design creates nothing more than a part
that is slightly different from the print dimensions, but missing a critical
shutoff fit will condemn the mold to failure or worse yet, hurt or kill
someone.

Of course, this all applies to varying degrees depending on the mechanical
complexity of the mold...molds that consist only of core and cavity, or
cavity and cavity, are pretty difficult to screw up enough to make them
unsafe to operate.

With regard to what CNC milling machine to buy, you probably have the sense
by now that it's an impossible question to answer until much more is known
about what you propose to make.
A case in point...the mold components are much bigger than a casual part
inspection would lead you to believe.
A two cavity mold for a part that is one cubic inch will be about 6" x 8" x
8" minimum, if it is to be used in a commercial press.
That means you don't have a prayer of building it on a Sherline unless
you've got LOTS of spare time.

You'd probably be better off spending your money on a Bridgeport sized
machine, and giving up the CNC bit, unless you're very well supplied with
cash.
Don't forget, complex molds were built long before CNC became available!!!

Hope this helps

Cheers

Marcus