Bridgeports (revisited, I'm sure)

So my brother finds out about my CNC project and his eyes perk up.

He's got four bridgeports in his shop that he'd love to have up refitted,
but he gave up on it a while back because it cost too much, as much as he
could get a new (used) one for already outfitted. The kits were 5 Kbucks. So
I did some quick math and figured he could have it all running for 1500,
more or less.

So now I get to do all the electrical work for him. (Granted I'll get
payback with some free production work.)

Searching this list came up with a couple of links. One guy fixed his up
with motors and timing belts but no pictures. The rest of the postings
(there were a lot of them) quickly deviated from info useful to me.

Anyway, the significant work (for me anyway) is sizing the servos and
gearing. I can use high power units and get the table acceleration up, but I
don't have any of this quantified, even the mass of the tables.

I can see a need for high acceleration if you're drilling a huge array of
holes, and he mentioned that 90/sec is good enough for fast movement, but
that doesn't require much power, it's the sudden stop at the end that draws
power.

One of the units have linear encoders on all three axises. He wants to use
them for feedback to EMC2 as opposed to the shaft encoders in order to
eliminate backlash. Does EMC2 support this, or will the servos oscillate
within the backlash?

And bottom line, how big do they need to be? If it needs high acceleration,
can I drive the motors with controlled surges? Would it mean being forced
into brushless servos to avoid high currents through the commutator?

I've got the electronics and computer stuff covered, BTW.

Dennis


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