Crank opperated hydraulic?

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?
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One would think that pneumatics would deserve consideration? Air cylinders etc.
i
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wrote:

Tight space considerations and, air is jerky and abrupt. The application will power a shear that needs to cut smooth. Sorry I didn't mention that.
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Tom Gardner wrote:

Why add the hydraulics?
--Winston
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Here's a pix of part of the mechanical:
http://metalworking.com/DropBox/_2004_retired_files/ob-shaft_timing.jpg
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this also sounds like a pneumatic cyl would work to me
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Tight space considerations and, air is jerky and abrupt. The application will power a shear that needs to cut smooth. Sorry I didn't mention that.
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A cam, follower, and lever would give you everything you need.
--

Dan

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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 more failure!
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On Sat, 05 Aug 2006 03:54:17 GMT, "Tom Gardner"

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 hour.
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wrote:

Hi Don
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.
Jerry
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wrote:

Yep! The grey area is, can I get the speed? I know hydraulics = leaks! But, we could hard pipe it and weld everything.
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On Sat, 05 Aug 2006 14:13:37 GMT, "Tom Gardner"

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.
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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.
--
Anthony

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wrote:

You and your voice of reason...buzzkill!
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wrote:

Hi Tom
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.
Jerry
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On Sat, 05 Aug 2006 22:42:43 GMT, "Tom Gardner"

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.
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The pistons have nearly no travel, but only transmit force.
Nick
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Tom Gardner (nospam) wrote:

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.
Dan
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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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