On Sat, 6 Sep 2008 21:57:02 -0400, "Tom Gardner"
wrote:

I need about 67 rpm on a shaft.
An 1800 motor with a 40 to 1 gearbox = 45
An 1800 motor with a 20 to 1 gearbox = 90
Of course, Automation Direct doesn't have a 30 to 1 box and I want to use
them as a supplier.
The output of the gearbox will have a belt to drive the shaft but should I
use the 40 and step up the speed to the shaft with the appropriate sheaves
or step down the speed from the 20? Or, does it not make any difference?

Torque doesn't factor into this, I'm upgrading from 1/10hp single phase to
1/3hp 3-phase...and it's CHEAPER!!!

I would step down from the 20.

If you step down to below load speed and then step back up, the max
torque in the system is greater than load torque. Not that it matters
in this case but I thought I'd mention it.