Re: [CAD_CAM_EDM_DRO] B/S vs. acme was Re: What makes a machine CNC ready?

At 08:00 30/06/2006, you wrote:

>11) acme, as well as regular 60-degree screws generally have higher thread
>count per unit of length, meaning more screw rotations are needed to advance
>the screw the same distance compared to ball screws. This has several
>advantages, one of which being that you can use a motor with less torque to
>drive the screw.

Well that depends not only on the relative pitches, but also on the
relative efficiencies of the two screws, which comes back to where this
discussion started...

For example, if we had a 4mm pitch ballscrew that was delivering 90%
efficiency vs a 2mm pitch Acme thread that was not one of Fred's exotic
Teflon-coated jobbies with bells & whistles, but a "cooking" variety screw
that was delivering an optimistic 40% efficiency, then the Acme screw would
require *more* torque from the motor, despite its finer pitch, not less.

Just goes to show that one should beware of making generalizations
(including this one!)

Regards,
Tony