coarse pitch ball screws

[endgrainguy]

Despite having some misgivings, I bought an Ebay bargain, 20 mm diameter, 20 mm lead ,nsk ground ball screw and nut and then afterwards saw the caveat against coarse pitch screws on the "ball screw basics" thread here. I guess I don't understand why it won't work well -the screws are very accurate, and can't one simply set driver for high microstep (maybe 1/10) and get plenty fine resolution? Or is the coarse pitch incapable of sustaining much of a load? Still, it would have to be far better than the Dumpster CNC antibacklash nuts many use? I'm planning on using this afor a 25" long Y axis for a moving table on a fixed gantry woodworking CNC router. I don't need high speed -50 inches/minute would be fine, but it will be doing inlay work, so high accuracy is required -- by woodworking standards anyway -maybe .002-.004 combined backlash/repeatablity. Here's my screw; http://cgi.ebay.com/ws/eBayISAPI.dll...m=260235880436.

[Mike Everman]

I'm a big fan of coarse pitch screws. I've been making pick and places with a 20x40 pitch that go 2.5m/sec.
The only downside to coarse is that axial stiffness starts becoming more about torsional stiffness. This won't crop up in most wood routing uses, IMHO; definitely not in the pick and place arena.
I'd just throw a 2:1 belt pass on the end, and think of it as a 10mm pitch screw.
Ah, I just remembered the other great thing about a coarse pitch screw used this way. Accelerations for the coarse with a 2:1 belt reduction will have 1/4 the screw inertia to overcome, so more acceleration with less motor, which is of course most important when driving through tight corners at high ipm.

[ger21]

For a wood machine, the only downside to high-lead screws is loss of resolution, and the fact that they require more torque to provide a given force.