Buffing speeds & flex shaft?

[Tallman]

I ordered the wheel polishing kit and the Zoop seal, and I read through the online buffing booklet, which states:

"For best results your wheel should maintain a surface speed of between 3600 & 7500 surface feet per minute (SFPM).

SFPM = 1/4 x diameter of wheel x RPM"

Why is it 1/4, wouldn't it be Pi (3.14) x Diameter x RPM? Just curious...

Anyway, it seems that a grinding wheel is a good choice, so I will borrow a friend's Craftsman grinder. I can't imagine not using a flex shaft to polish 18" car wheels with this, but no one seems to sell them for bench grinders. Surely someone has them? I have a Rotozip too, but it runs at 24,000 RPM I think...would that work as well?

[skiddz]

Your formula is correct. Pi times diameter times RPM will net you a correct SFPM. For aluminum, shoot for right around 5,000 SFPM. A 6" wheel at 3450 RPM will get you up around 5,400 SFPM which is right in the ballpark.

I cobbled up a SFPM calculator with javascript and put it here:

http://users.adelphia.net/~skiddz/Wheelspeedcalc.htm

It's ugly and kludgy, but it works. :)

There are flex shafts out there that you can run from your buffer. I've got one I run off my Jet 1hp buffer and it works great. I don't think the RotoZip would have enough torque to be very effective at buffing. I've also got one of these things and other than sink cutouts and the occasional oddball drywall cutout, it's pretty useless IMO. :)

[mtlgd]

Originally Posted by Tallman

[img]
Why is it 1/4, wouldn't it be Pi (3.14) x Diameter x RPM? Just curious...

The long form is (Dia. X Pi) / 12 x RPM = SFPM

Dia. and Pi are in inches. Dividing by 12 converts it to feet.
For general purpose Pi / 12 is simplified to 1/4.