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Reply by Dan Krager

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Posted on Are Most Benchtops Woefully Underclamped during Glueup? (probably not)

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Dan Krager

1465 posts in 830 days


#1 posted 592 days ago

One of the tricks to generate enormous pressure in a home shop is to use air bags in a trapped enclosure. If a veneer press type cage (think heavy truck) were built with thick plate cauls (stacked plywood) an air bag (think car tire or bigger) will generate monstrous pressure.
I’ve heard of using a section of discarded fire hose as a linear air bag of sorts. Again a containment vessel is required. Lay the prepared and collapsed fire hose (may be folded once) beside the edge of a glued panel within the containment and apply pressure. Edge clamp pressure can be enormous. The hose is prepared by cutting off whatever length is needed, leaving the fitting exterior to containment. The fire hose fitting is then fitted with an air hose supplying regulated pressure. Careful welding may be required for that adapter.
Now, to the math. Suppose you can get 100 lbs PSI in the fire hose (they can hold several hundred psi safely). You’ve got 384 sq in, so let’s see, um, um, wait… I’ll get it… um 38,400, yes that’s it 38,400 lbs against the edge.

Hydraulic pressure is an underused pressure resource in a wood shop. Bottle jacks tend to be cheap, but I guess it’s the frame that gets expensive. Three 20 ton jacks can generate 120,000 lbs, but what’s going to hold it? I have been known to use accessories from a hydraulic ram kit, structural I-beams…whatever it takes.
DanK

-- Dan Krager, Olney IL http://www.kragerwoodworking.weebly.com


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