"Eric R Snow" wrote in message
...

As Anthony said, replacing the aluminum pieces with steel would be
best. Bronze nuts for the steel leadscrew will work best. You should
be able to buy split nuts. These have a screw that pulls the two
halves of the nut together to minimize backlash. Also available, but
harder to adjust in the location you must put the nut in, are nuts
which screw together. The thread that holds them together is a much
finer pitch that the 5 TPI for the leadscrew. Screwing them in or out
changes the backlash.

Ah, that kind of nut sounds like a really good way to go. Do you have any
leads on where to find these? I haven't seen them in MSC or McMaster.

If you are really going to put CNC on this mill
later consider doing it now. The CNC should use ballscrews. They have
much less friction. This lack of friction makes them unsuitable for a
manual machine because they self feed easier. So when climb milling
the table lock must be set to drag enough to prevent the cutter from
dragging the work into it and breaking things.

That's kind of a way out, and I'd rather have a working mill than an ongoing
project right now. Thanks for the pointers.

As far as shipping
damage goes, if it arrives damaged send it back. And why should the
choisest part of a new screw be in the middle? Are you planning to
measure the lead error?

Nope, just have come to expect damage in handling, even with something
labeled precision. Your points are good.

If so, I guess you might find a three foot
area in the six foot length that is best. BTW, I've bought acme screws
several times in the last 25 years and they have always been much
better than the maximum error allowed. But I've always bought USA
made. I have seen leadscrews from Taiwan that were terrible. I made a
little stepper driven X-Y stage to put on the Bridgeport for milling
small complex curved parts and the screws it came with were visibly
out of tolerance. The thread looked like the die was wobbling while
cutting the threads.

I've been trying to keep to American-made materials in projects; with this
one it's a no-brainer.

Thanks!!
Pete