[kevincnc]

I happened to measure the ballscrew on our Morbidelli today. It's 30mm, with a rotating nut, and moves a 1000lb+ head at about 1500ipm. There's about 13ft of travel, as it's a 5x12 machine.

Does that have pop-up supports to keep the screw from sagging when the head is at the far ends?

[harryn]

I have been looking a lot at class 3 ball screws lately vs rack and pinion. Roton (and others) have 1 inch dia x 1 inch lead (1 turn per inch) class 3 screws as a standard, off the shelf product.

A direct drive (through a coupling) stepper to a screw like this, it is very similar in rpm, torque, speed, and resolution to the cncrouterparts pro rack and pinion setup. As far as I can tell, the class 3 ball screw will be at least as accurate as the rack and pinion seutp, and possibly even more so, because of fewer components between the motor and final drive.

This puts the ball screw rpm into very reasonable speed - often only 100 - 200 rpm for a lot of hobby cutting projects, which means that quite long setups are possible. 6 ft was the longest I found on Roton, but Thompson will cut them longer.

I am still looking at the "total" cost of these seutps, but at least for 3 and 6 ft, it looks similar. The main challenge for me, remains economical screw mounting, but I think this can be done (for hobby use) at a reasonable price. Pro level ball screw mounting is really good, but not cheap. The difference in price between a 1 inch lead screw and 1 inch class 3 ball screw was really not that different - $ 25 vs 35 per foot.

Coming back to the belt drive question, the main challenge is the lenth:width ratio. If you use a belt for cnc wood routing, target a length to width ratio of around 10 - 15:1. ( example - 60 inch long belt, target a 4+ inch wide belt) A 60 inch long x 1 inch wide belt will give mediocre results at best. I like belts, but 4 and 6 inch wide belts start to be difficult to place in constrained locations.

[ger21]

Does that have pop-up supports to keep the screw from sagging when the head is at the far ends?

It's got a small single support that looks like a wheel in the center. It's mounted on a spring loaded bracket to pivot out of the way when the head moves by. I've never actually watched it while running, though.

The Masterwood we had at my last job had a similar screw with no support at all.