Reply by Nicholas Hall

@Crank: Mathias 10 times the woodworker that I’ll ever be, and he’s smarter too. That said, you’ll note that that he’s exterting a massive amount of pressure in his “high pressure” joint. It looks like he’s clamping maple. He’s using 4 c-clamps on a 1.575”x1.575” area. Cheap ductile c-clamps generate 2800 pounds of force. So we have 11200 pounds of force over 2.48 square inches. That’s 4500 psi. The chart above says 1200 is optimal for maple. The author of the article does say that it’s possible to starve a glue joint, he says it’s unlikely to happen outside of a labratory.

Here is a link to c-clamp force measurement: http://www.newmetalworker.com/reviews/besycclmpvar.html

Still Mathias’ experiment is very interesting. What it lacks is a control of sorts. He massively overclamps some, massively underclamps others, but none of his test cases evaluate the strength of a normal joint that most woodworkers create. He uses 4800 psi for the overclamping an 1psi for the rest. I’d love to know what the strength would be at the optimal pressure.

-- “Congratulations. You’ve just figured out the most complicated way to hold a board 30 inches off the floor." Tage Frid