On Sat, 16 Jul 2011 15:24:04 -0700 (PDT), Jim Wilkins
wrote:

On Jul 16, 1:01*am, wrote:
...
7) Thanks to the gentlemen who provided me with the formula. I found
it independently in the Machinery' Book late last night after I
posted. I should have found it much sooner if I fed "jackscrew" into
Google. Such is life :-). The figures I got was 125x multiplier
without friction. I tried to do the calculations with an assumed
coefficient of friction of 0.2 and got a multiplier of 31.5. Seems
kind of small. I haven't the foggiest what kind of force I put on the
end of the lever (3" long, BTW, the pitch is 0.151" and the pitch
diameter roughly 0.6").

Michael Koblic,

I think up to ~80% of the tightening force on a screw can be lost to
friction. Compare the torque to tighten with that to loosen.


I guess they are different :-) ??

I re-did the calculations using the 2 formulae in the Machinery's
Handbook: One for when the motion is in direction of the load
(assisting it) and the other in the opposite direction (opposing).

With the same data I got the force necessary to move a load of 1000 lb
to be 6.66 lb in the first case and 9.68 lb in the second case. This
time the multiplier is 103 and 150. GOK where that 31.5 came from. The
multiplier without friction is smack in the middle. That makes sense,
does it not?

Michael Koblic,
Campbell River, BC