wrote:
Thank you very much for your all's time.

As for MaxNC, that's out of the question for us since we'll end up
frequently manufacturing parts greater than the 12 inch travel.
For the safety question, we've gotten a ok for a manual mill as long as
there is a machinist watching over, and there is restricted access (to
ensure some of the more careless members dont play with it like a toy).
We've also been fairly careful with our handeling with machine tools
and even though it is a risk, we think its one worth taking (for the
things learnt).

"
Truly +/-.001" on a bridgeport is pretty tight, but certainly
attainable.
What kind of work are you doing that requires such a tolerance? "
We manufacture our own high-speed gearboxes whose mounting plates
require about 1/1000th tolerance. we've previously found that even
1/1000th off can cause the motor to bind and start flipping the
breakers, or cause unacceptable current draw.

This is where you need engineering input. You do not need to hold tight
tolerances to get good alignment; you need to have adjustable mountings
and have good alignment procedures, and/or use couplings that allow
misalignment. Keep in mind that what starts out aligned might not stay
that way under various loadings.

That said, I shoot for tight tolerances on everything I make. Failure
to do so leads to a downward spiral of corrections for errors in
corrections for other errors. I recently made a part with a channel
that snakes from one side of the part to the other, with through holes
connecting them. That required flipping the part and reading the
drawing from the other side; it worked, but would not have been so
"easy" had I been sloppy with the dimensions.

Good machinging is always desireable, but it is no substitute for good
design.



As for the mill, we are in fact located in California (bay area,
however.) , so we are highly interested in Gunner's offer of a Shizuka
CNC mill. If that is not possible, we can of course, go for a
bridgeport, or we've also been looking for something like
http://www.industrialhobbies.com/ the square column mill. The work
envelope is more than adequate, it seems to have a strong enough motor
for our work, and the spindle speed seems okay for aluminum work. the
Free shipping also makes it very attractive for us.

I have no CNC experience, but my instincts align with those saying that
manual experience is essential to CNC work. It would be very easy to
instruct a mill to take a dangerously deep cut. There is a lot to be
said for feeding manually before engaging a power feed, at least for
rough cuts, and especially when cleaning up uneven edges.

In general, I suspect you would be better off without a DRO. If you
want to learn, learn to navigate w/o one. A steel rule and a small
drill bit allows you to get within 0.1 inches, at which point the dial
readings become meaningful. A machine with uneven wear on its screws
weakens this argument.

Bill