I had an idea of a crank operating a hydraulic cylinder connected to another
hydraulic cylinder that would do the work. I need about 300 lbs force with
a 3/8" stroke. I need the cylinder to cycle an extend and a retract stroke
in 250 to 300 milliseconds max. and do it 90 times a minute or more. It
sure would simplify a complex mechanical system. Is this possible? Is there
another way to do it?
That's where I'm at now. The first machine had a cam that we chanced to an
eccentric roller bearing. We improved this on the second machine by
optimizing the lever ratios and such. I'm thinking about the third
machine...what ways I can simplify it. They take nine months to build and
it's several hundred machined parts...one at a time! The more parts, the
Might be a good idea. The benefit is that it can remove mechanical
complexity away from a crowded place, leaving just a small hydraulic
actuator "in the zone". They do that a lot in aircraft and
missiles. Ditto automotive brakes -- small wheel cylinders do the
job with comparable strokes and forces.
The force and stroke you cite are certainly compatible with
readily-available hydraulic components.
There are details to consider, like effects of leakage and making
sure the motion at the driven end will stay in spec if there is some
leakage. Mechanical systems retain geometry, and hence expected
motion, unless/until something deforms or wears.
All hydraulic systems with sliding or rotational seals leak, it's
merely a question of how much -- molecules per decade or ounces per
What do you know about automotive anti-lock brake apparatus? It seems
that the devices within the car's brake system, coupled with a pump could
drive a cylinder far enough and fast enough.
It seems that a anti-lock system from a wrecking yard might be modified to
provide the hydraulic displacement from an electrical pulse. I'm thinking
automotive valve spring for piston return.
If you have a double-acting system, and it sounds like you would,
you'll still have some seepage around a gland seal. No big deal, but
the design would need to accomodate that -- i.e., keep working right
even if a little fluid is lost over time.
Don't see why speed would be any problem. Antilock brakes are
hydraulic, pulse a lot faster than a couple hundred milliseconds.
ABS systems use solenoid-actuated valves. Your setup could use that,
but a simpler setup might be more like hydraulic valve lifters, where
you produce the desired motion mechanically in one location and then
use hydraulics to replicate that motion elsewhere in a tighter place.
Speed: A change in pressure travels thru a hydraulic system at close
to the speed of sound in the fluid -- which is considerably faster
than it is in air. In a system with a few feet of hydraulic line, I
would think that operation at frequencies up to 100 Hz (cycles per
second) would be no problem.
One issue could be wear. Your hydraulic gizmos will be cycling back
and forth over a short range at 90 strokes per minute, or 43,200
strokes per 8-hour shift. I don't know how many strokes hydraulic
cylinders are good for before they need a rebuild.
Yup, but they are only pulsed for short periods of time. Not a 24/5
operation, nor even an 8/5 operation. The other thing is...anti-lock
brakes are mostly relieving pressure that has already been applied.
You can't 'idiot proof' anything....every time you try, they just make
I've seen some hydraulic hammers and chisles that dont leak noticably
after a year of hard use. I think Don's idea is worth trying, unless there
is a better method available.
I'd expect a routine maintenance schedule could provide a high degree of
functioning time on Don's type system.
Not necessarily. I said I don't know -- they may be good for millions
of operations between rebuilds. They might well outlast mechanical
bushings,bearings and cams for all I know. It's certainly worth
checking. Someone mentioned diesel injectors as one example.
While you are thinking about the redesign, is there any other places
where hydraulics would work well. I am thinking that if you had a
hydraulic pump and accumulator, you could use a spool valve to actuate
the shear. And could use hydraulics for other things as clamps.
Air already does a bunch like clamps, wire advance, lock-outs and such.
Actually, I think now after airing it out that we have the mechanical
sollution perfected to the point of maturity. I'll know better after this
second machine gets some experience and shows it's weeknesses. Number one
went through some retrofits at the 6 month mark and has a <5% downtime
record. I want <2%. and cheap fixes.
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