roller screw versus ball screw.

[Paraprop]

Considering an application like the retrofit of a Bridgeport Knee Mill , is there any advantage to substitute the classical ground ball screw (32mm diameter, 5 mm lead, 13 micro m. / 300mm) by a roller screw like the ones manufactured by SKF ?

Daniel

[Zumba]

It's similar to the comparison between a needle roller bearing and a ball bearing. Rollers larger contact patches than balls, which equates to higher load capacity. The Nook website shows that a 25mm x 5mm roller screw has an 11000lb dynamic load rating, whereas a 25mm x 5mm ballscrew has a 2000 lb rating.

But a bigger contact patch means more friction of course, so it'll limit your top speed. Again, just like how the max RPM of a roller bearing is typically much lower than that of a ball bearing.

Speed won't really matter on a Bridgeport, but neither will load capacity, since the screw is definitely not the weak link on a BP mill. Did you find a pre-owned set of screws? If you're buying new, I'd just stick with ballscrews.

[Paraprop]

Thanks for the advise.

I'll try to get a set of ground ball screws then. Don't trust second hand ones.