Acme threaded rod, formula for torque

I plan to use a 3/4" Acme threaded rod in a vertical position. The nut will support a 250# load. The rod will rest on a needle thrust bearing. Is there a formula to compute the torque required to rotate the rod ay a specifies rpm?
Don Morse
dmorse02@twcny.rr.com

 

[RLJ]

Don,

I will assume that you are using a combination style needle bearing with rollers or ring to carry the thrust. I have some information from Marks Standard Handbook for Mechanical Engineers that may help. This info deals with calculating the torque using a ring for picking up the thrust. If interseted I could type them out here, scan/email or fax to you. RLJ s-)

 

I will be using Torrington 1220 thrust bearing with races. All I have been able to get so far is that TAPERED screws are 65-85% efficient-not much to go on. If you have info, pls send to:
Don Morse
dmorse02@twcny.rr.com