On Sun, 17 Jul 2011 05:33:47 -0700 (PDT), Jim Wilkins
wrote:

On Jul 17, 7:53*am, " wrote:
...
This seems too obvious to mention, but I will anyway. *The friction
depends on the lubrication. *A ball bearing thrust bearing or a roller
bearing would also help....

Perhaps you could incorporate Belleville washers to give you an idea
of the force applied. *Belleville washers can be stacked to increase
the force necessary to flatten them.

* * * * * * * * * * * * * * * * * * * * * * * * * * Dan

IIRC experiments on torqueing aircraft fasteners showed a 2:1
variation in clamping force vs torque from surface roughness etc under
the best conditions. A skilled mechanic's judgement was as good as a
torque wrench. The best way to torque a fastener to a large fraction
of its yield point was to measure the change in length, though that's
not always possible. I saw that in print a long time ago.

I saw the same data which is where I got the idea to incorporate a
torque wrench into the design. Then I got completely confused looking
at the recommended torques for tightening bolts - the figures seemed
to exceed the tensile strength of the bolts.

The bottom line is you have no good way to predict what's happening
and should measure the forces.

Even some sort of indirect method would be useful to achieve
consistency. Stick a lump of rubber in the press and measure its
distortion?

Michael Koblic,
Campbell River, BC