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

What Ron Moore said.

Will the budget stretch to $160 for a 1 HP VFD?
http://www.vfds.com/inventory.html#drives_0.125

Use the 20:1 gearbox and set the VFD to 74.44%?
Perhaps use a heatsink on the motor to compensate
for less 'fan effect'?

--Winston