"Jim Wilkins" writes:

...
As for the eccentric, I considered it because you could vary the
piston stroke, but you'd need a lathe to make it, the pump drive is
more than a friend could whip out in a spare hour. A pump built into
the cylinder end might give the fastest cycle rate because there's no
flow restriction. You could fine tune the peak pressure during
operation with a screw that displaces oil. A cheap used tie-rod
cylinder with a scratched bore could be cut down to be your pressure
chamber. Cylinder rebuilders can provide the tubing in any length.

On my tractor's homebrew bucket loader attachment hydraulics I turned
the head of a bolt round and grooved it for an O ring, so it can screw
into or out of the oil space without leaking. It operates the variable
pressure relief valve I made to replace the fixed relief the control
valve came with. The tractor's front tires turned out to be the
weakest link that limited how high I could set the pressure.


Variable - you have many eccentrics, each with a slightly different
throw?

I thought - one eccentric, but many different "pistons" with their
"collar" they go through into the fluid volume.

Yes one thought is that the mechanism could be built onto the lower cylinder end.

With the "bar" driven by the eccentric simply pushing in and out of
the cylinder volume.
For the "170Tonne-force" test it would need to displace about 270cc -
would be 70mm diameter and stroke (or some other combination of
diameter and stroke which gives that displacement).

One advantage of this arrangement is, seeing as it's so stiff, plus
bits can't fly around with being inside the cylinder, the test rate
could be high. Fastest induction motor speed? 3000rpm on 50Hz supply
= 50Hz test rate :-)
That would be 60Hz on N.Am. supply.





The decision comes down to what you can build or buy. I've spent
significant time and money becoming able to build what I or the
customer wanted, electrical, optical and mechanical.

Knowing the metallurgical and fatigue stuff has cost me a lot - money
in various ways and time ...