Reply by Nicholas Hall

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

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Nicholas Hall

352 posts in 2103 days

#1 posted 12-07-2012 01:20 AM

@Danny B: A pipe clamp exerts 1050 pounds of force. The psi that it exerts is a function of the area over which that force is applied. If it is applied to a nail it will be over 10000 psi. If it is applied to 100sq inch caul it will be 10psi. The chart in the post says maple needs 1200 psi. To acheive this over a 384sq in area will require 345,000 pounds of force. My question is not how to distribute the 345,000 pounds of force. My question is how in the heck could a woodworker ever generate that much force in the first place.

Here is the text from the article regarding the calculation of necessary force:

“The first step when gluing boards is calculating the
square inches of glue surface. For example, if you
are gluing two boards 3⁄4 in. thick and 36 in. long, a
single glue surface equals 27 sq. in. Even if you are
edge-gluing several boards, you still need to measure
only one glue surface because the clamping pressure
is transmitted across the width of the boards. If you
are edge-gluing flatsawn red oak boards and wish
to apply about 450 lb. psi, then 27 multiplied by 450
equals a force of 12,150 lb. that must be applied. Using
the average of the editors’ clamping forces, this
could be supplied by around nine heavy-duty bar
clamps, a dozen 3⁄4-in. pipe clamps, or 26 quick-grip
clamps. Obviously it would be hard to fit 26 clamps
along a 36-in. board, so add some more powerful
clamps if you have them. It’s fine to mix and match
types of clamp.

Here is a link to the article:

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