# Clamps and PSI



## Stephen_Adelaide (Apr 9, 2013)

Hi,

For a softwood the recommended psi is 100-150psi (eg. Titebond recommendation) and a sash clamp can apply ~400psi (ball park). However, is this divided over the distance of clamp contact with wood?

What it boils down to is how do the Titebond recommendations relate to how many clamps will be needed?

Their recommendations are that 100-150 for softwoods is needed with clamps every 12 or so inches. Does this mean that you need a clamp capable of delivering 1200psi for that 12 inch distance to make the minimum psi recommendation? Or, do they mean that you need a clamp delivering 100 psi and this will be delivered to all 12 inches and the psi in effect is not divided?

Hope this makes sense, 
Stephen Young


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## mojapitt (Dec 31, 2011)

This has been discussed before. The more clamps the more evenly it will be. However, clamping doesn't compensate for bad or uneven cuts.


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## redSLED (Mar 21, 2013)

As long as your boards line up nice and even, just clamp 'em all tight. Wait 30-60 sec. later and clamp them all tighter. A little more glue is better than less. Add more clamps if you have them. Your wood surfaces should be coarser than finer (use a rasp, file brush, whatever). I've seen unbelievably strong miter joints held together with Titebond only - achieved with medium clamping pressure even. I've never had glued-up pine boards (no biscuits or screws) come apart later - and that's with using basic carpenter's glue and bar clamps.


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## Viktor (Jan 15, 2009)

A clamp by itself exerts force (lbf), not pressure. That force distributed over an area is pressure (psi). If the manufacturer recommended pressure is 100 psi you need one clamp capable of delivering 1200 lbf per every 12" of 1" thick board. However, manufacturer recommendation in this case is a vast exaggeration. If the fit is good 1/10 of the recommended pressure will be sufficient.


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## Loren (May 30, 2008)

In factory settings, you might mill and straight-line rip 100s
of board feet before gluing it up. In a small shop it's
both wise and easier to make your boards straighter.
Industrial clamps are relied upon in factories to close 
glue joints in parts that have moved due to the volume
of work being done.

I have some industrial air clamps and they are frighteningly
powerful, but I still try to be mindful when milling 
boards for glue-ups, because I like a fine joint and I don't
like glue all over the place.

Heavy clamping pressure does come in very handy
when doing bent laminations though.


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## Stephen_Adelaide (Apr 9, 2013)

Thanks guys for the clear and helpful answers.


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## renners (Apr 9, 2010)

I found this to be a real eye opener

http://woodgears.ca/joint_strength/glue_methods.html


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## redSLED (Mar 21, 2013)

^ That is a very good glue-up read.


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