[steamer]

It's pretty ease to figure out screw drive RPM. Just measure one inch of the thread and count the number of threads in that inch. That way your know how many turns of the the screw it takes to move one inch. If the screw has 32 tpi. and the gear drive is 32 it's going to take one minute to move that 1 inch. If you want to know yours count the threads on your screw, time how long it take to travel the inch and you'll know the RPM
Say the thread pitch is 20 and it takes 15 sec. to move the inch.
Take 1 min.= 60 sec Div. by 15sec.=4x20tpi =80RPM
So it's going to take 80RPM to move the 20tpi.screw 1in. in 15 sec.
Rob