"Richard Smith" wrote in message ...

...
One circular eccentric disk, mounted on an offset pivot pin so it can
be centered or swung out as needed. The clamp for the swinging side
might have to include a custom stepped bushing to withstand the
torque, rather than just a bolt that holds by friction, but its
surface finishes aren't critical like the eccentric's. ...
jsw

I haven't got this for certain.
Not grasped the idea for sure, yet.

Forces would be in Tonnes to tens of Tonnes.
The size of the eccentric - both what it will withstand as a bend or
shear, and preesenting enough bearing surface for the bearing to take
the load - can make these things quite big. Maybe 200mm diameter with
190mm shaft for 10mm "throw", for some enormous tests in high yield
steels.
As I calculate / estimate as best I can.
RS

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Lets say the 200mm eccentric is pinned to its mounting plate with two
diametrically opposed 25mm round bushings. If the bushings are straight
cylinders the eccentric disk runs in a true circle. If both bushings have a
5mm offset step in the middle to shift the eccentric disk sideways the throw
is 10mm. The lathe setup to turn the bushings is the 5C collet block in a
4-jaw chuck, as in the posted reference.

The bushings provide high shear and bearing strength. They would be slotted
and keyed to prevent rotation. Making them is a reasonably simple lathe
operation. To change the throw you make bushings with different offsets
rather than changing the eccentric disk.

Two identical stepped bushings is simpler to describe, one stepped and one
parallel is more rigid, triangle vs parallelogram.
jsw
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If it came to making one of these things, there would have been a lot
of proof-of-principle with "testing lab. scale" samples, and the
stakes would be quite remarkable by that stage, if we got there.

The main point is to have plans in place.
In a political world, you have to have everything covered, so every
interjection, objection, etc. is smoothly put in its place.
As I've experienced.
I've certainly had the skill of predicting what the ploys might be
tested. Having big efforts to derail the plan slapped down in
seconds.

So it's about being able to see a way ahead, far along a perceived
path. What would actually be going on, where you would actually be by
then, what method you would use given experience had by then but ahead
of you now - that might be a different story.
But for now - you are "covered"...
RS

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Been there, done that, I was the lab rat who built the proof-of-principles
from sketches and gave the engineers simple, practical and economical ways
to convert their concepts into products. I provided you several different
approaches you could pursue, and mentioned possible sticking points like
difficulty of fabrication or programming, and the skills and equipment to
moved past them.

A very handy trick I picked up to counter objections is to memorize the
squares and reciprocals of numbers up to 32 so I could do engineering math
rapidly in my head and present an off-the-cuff mathematical basis for my
arguments. Above 31 [sqrt(1000)] they pair with lower numbers, 1/25 =
0.040, 1/40 = 0.025. Engineers not from the slide rule era don't learn the
simplifying tricks we had to.

For example I was running an error rate test on a satellite link when the
chief engineer demanded to know how much longer I would be tying up the
channel. The test was 10 million bits at 2400 per second. Knowing that 1/24
is 0.041666... I mentally figured the test duration as 4166.7 seconds, then
converted that to 1 hour (3600), 9 minutes (540) and 26.7 seconds and gave
him the answer. He pulled out his calculator, hesitated, then admitted he
didn't know where to start and left me alone to complete the test.

I understand the physics but it's still weird to see something stored and
later retrieved intact from empty space.
jsw
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With the beam tests, you can tune the testing force by moving the beam
end supports in and out - present different spans. So one fixed throw
/ movement drive would cover all purposes.

For the "hydraulic inner fatigue test", I think different diameter
"spuds" sliding in and out of the fluid volume, on a fixed eccentric
drive, might be easiest?
RS

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The most demanding part to make is the piston/cylinder sealing surface,
especially if you don't have machine tools. Any spud screwed into the end of
the piston displaces a fixed volume of oil. There may be another way but I
think the easy answer is to change the stroke length (lever?) unless you
collect an appropriate assortment of polished rod stock and seals (car shock
absorbers, gas cylinders etc). Modifying the rods into pistons and making
packing glands to retain the seals are lathe operations.
jsw