Thrust bearing idea needed

I'm toying with the idea of re-designing a custom tool we use. Essentially, it's a portable pin punch (to break welds) that uses an
air cylinder to drive a hydraulic intensifier and then pushes the punch. Yea, like that's portable (50+ pounds)
Currently we get about 7000 psi over a 5/16" dia tip. That's overkill for 95% of the uses. Typical use is a couple of hundred cycles at a time.
Anyway, one option is a rotating threaded bar to act as the pressure creating device (similar to a chain breaker only bigger). This would require a thrust bearing between the screw and the tip, as the tip cannot rotate. Any ideas on a thrust bearing system that would take the pressure and still keep friction down to the minimum? The bearing needs to be less than 1" diameter if possible. Using this the cycle time would be longer, but that won't matter as even a 20-30 second cycle would be ok. Takes a minute or so to re-clamp anyway so cycles are only a small part of the process.
Any other ideas on how to move a 5/16" pin to put a couple of tons of pressure with about a 1/2" stroke and still keep the thing small enough to work over your head if you need to?
BTW, already considered air powered hydraulic pump at 10,000 psi....is not quite idiot proof enough for our application. too many hoses.
Just searchin for any ideas
Koz
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Well, your threaded idea sounds fine to me but you need to crunch some numbers. If you are punching 1/4" mild steel with a 5/16" punch, then you will need about 6 tons of force. Let's assume your thread is 10 per inch, that means 360 degrees cranks you 1/10th inch. If you use a wrench that's one foot long then the tip of the wrench has to move about 75" to complete one circumference (diameter is 24", circ. equals PI * DIAM) during which the punch moves 1/10" so your mechanical advantage is 750:1 but if you cut that by 33% for friction losses you'd get 500:1.
To achieve 12000 pounds force your guys would thus have to push on the end of the wrench with a force of 12000/500 or 120/5 or 24 pounds. That is possible, but I know *I* couldn't crunch 24 pounds sideways overhead all day.
Grant
Koz wrote:

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Thanks for the ideas. Actually, this isn't a true punch. It breaks a perimeter weld on the inside of a 5/16" washer. The weld generally has only minimal penetration so doesn't take that much pressure. It's a little too much for a standard chain breaker though. Also, the clamping head needs to be compact and specialized for the parts so a standard "C" punch won't fit the bill. The current tool is overkill because it will do up to about a 1" washer.
I appreciate some of the ideas given though as they at least send me looking in a few directions. FYI, if the weld happens to be stronger than most, it can be ground down easily before punching. The idea is to alleviate doing this on all the welds though. Once in a while is ok, 50+% of the time is too much.
Wish I could be more detailed but I can't give away the store here.
Koz
Grant Erwin wrote:

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I think it's going to be difficult to find a 'bearing' that will do this, in that size. You might look into a bronze flat plain bearing.
--
Anthony

You can't 'idiot proof' anything....every time you try, they just make
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On Fri, 12 Dec 2003 16:25:25 -0800, Koz

Scheme I've used on clamps is a good-sized hard steel ball (1/2" or 3/4" dia) held captive in a cylinder and pushing on a hardened steel anvil with a dab of moly-D grease in there. A carbide ball and anvil might work even better but I don't know if they'd take the compression force or not. The anvil could just be an old TPG (ground surface) lathe insert!
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Koz wrote:

Have you thought of adapting a hand powered hydraulic puller? Princess Auto sells one (and I have no doubt other tool suppliers have them). Basically it is a small hydraulic cylinder pressurised by screwing in a threaded rod/bolt. This particular model (Part number 1259993, page 214 current catalogue) develops ten tons. catalogue can be downloaded here http://www.princessauto.com/PAcountry.cfm?CTRY N&INF=home You need lots of bandwidth for this. This tool is a bit of a pain to use as setup is awkward but worth its weight in gold when nothing else will do. I have found the gentle application of a 1/4 inch air impact greatly improves performance. The hydraulic setup does solve the 'rotating' problem. Hope this helps. Ken.
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kmiller@*dontspamme*metalbelt.com says...

It might be worth a look at some of the KO punch pullers that Greenlee makes, both hydraulic and mechanical. Lots of force in a small package.
Ned Simmons
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On Fri, 12 Dec 2003 16:25:25 -0800, Koz

You might look at this. http://surpluscenter.com/item.asp?UID 03121400365756&item=9-4122&catname
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