"Richard Smith" wrote in message ...
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My tension test rig is cruder, a chain hoist or porta-power hydraulic pull
back cylinder between two large trees. Since I have machine tools I can
reduce the size of the sample, and thus the force to break it, to within the
range of my load cells.

I restrain the broken ends with large ratchet load straps meant to bind
loads on trucks. Also the D-handle ratchet will apply up to 1000 lbs of
pull, enough to drag my pickup truck through a snow bank, so they are tow
straps with a built-in winch for self-recovery, though I wouldn't trust them
for towing by another vehicle.

I did my youthful off-roading on a dirt bike I could muscle out of
waist-deep mud holes, not like my buddy who got his Land Rover balanced on a
stump with all 4 wheels off the ground. The club I was in practiced
motorcycle Trials to include riding over stumps, boulders, picnic tables etc
at balance-challenging low speed. They also raced on frozen ponds, with many
of the spectators in leg casts. Some people here also practice the opposite
of motorcycles on ice, snowmobiles on water.

I thought it was handy that you could remove a plate to access and repair
the Land Rover's transmission from within the vehicle, but disturbing that
they knew you might have to. I added such an access plate to my VW Beetle
where it greatly helped unbolting the engine and starter for repairs.

My job during and after high school was in the lab of a leather factory that
made pump cup seals, flat and round drive belts and traditional leather
parts for looms such as check straps. Their chemist was researching
synthetic replacements for leather and had a Tinius Olsen tensile strength
tester to compare elongation and breaking strength, which I operated.

The machine's mechanical operation was simple enough that I copied the
design to raise the head of my sawmill. Two thick vertical lead screws
slowly raised the crossbar that held the upper clamp. The tension indicator
was a dial spring scale with carbon-piston damping cylinders to reduce the
shock of snapping back to zero. The black pointer pushed a separate red
pointer that recorded the highest value until reset. I have an abused and
hopefully repairable 600# dial tension tester scale in my collection,
reputedly from MIT.

I don't know what the machine had for thrust bearings but I've had good luck
with greased stacks of alternating steel and brass washers when the load
exceeded the PV rating for rolling bearings. On my sawmill the two
leadscrews are coupled with bicycle chain and sprockets.