Popular Woodworking 2001-08 № 123, страница 4
Out on a Limb
We did our own research, and the results are . . .
There's a legend about the early woodworking days of Sam Maloof. Seems that one day Sam wanted to test the joint strength of a table or chair leg.
Sam's test didn't involve rigorous scientific methods. Being a practical guy, he took the mocked-up joint to the second floor of his house and chucked the thing on the driveway. The joint didn't break and Sam was satisfied.
In that same spirit, we decided to get to the bottom of the debate over which is stronger: biscuits or mortise-and-tenon joints. We were ready to fling two open-sided cubes off a water tower. But then I
through the eye bolt and then attached it to the anvil. On top of the cubes we set a 2"-thick, 16"-wide piece of birch.
It was amazing. In truth, we all thought the first drop at just over 4' would barely cause any damage.Were we wrong. On the first drop, the cube with biscuit joints was destroyed. The sides that took the brunt of the impact had their joints completely sheared off.
The mortise-and-tenon cube fared better. It survived enough of the first drop to warrant a second whack.
We examined the joints, and here's what we concluded. First, take care not to
The anvil about to hit the cube made from biscuits.
The cube made from biscuits after impact.
The mortise-and-tenon cube after the first hit.
The mortise-and-tenon cube after the second hit.
realized a flaw in Sam's test. Furniture is rarely thrown to the ground. In reality, all sorts of objects land on them, be it an abundant backside on a chair or a heavy object on a table.
So there was only one real test, and all the staff here knew it. Hey, we all watched poor old Wile E. Coyote try to drop that anvil on Roadrunner hundreds of times, only to become the victim of his own making. One phone call later, and a 100-pound anvil from Grizzly Industrial was on its way.
We constructed two cubes, 24" on each side, using 7/s" x 3" poplar. For one cube, each rail-to-leg joint was made using a ^s"-thick x 2"-wide x 13/s"-long tenon. The legs were 2" x 2". The other cube was joined using two #20 biscuits in each joint. All joints were glued using Titebond.
To drop the anvil we set up a beam with an eye bolt. We threaded nylon rope
drop 100-pound anvils on your furniture, no matter what joints you use. Next, as we have concluded before, the wood always gives out before the glued joint does, whether it's a biscuit joint or a mortise and tenon. Last, the length of the tenon relative to the biscuit, along with the rounded shape of the biscuit, gives the mortise and tenon greater mechanical strength, glue or not, than biscuits.
Other observations? Biscuits are not a good choice for the kinds of stress that chair joints receive. If you know that what you are building will have to withstand repeated, heavy stresses, don't use biscuits. For regular woodworking biscuits are fine. And, oh yes, it was a lot of fun doing the test! PW
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Manufacturers place safety devices on their equipment for a reason. In many photos you see in Popular Woodworking, these have been removed to provide clarity. In some cases we'll use an awkward body position so you can better see what's being demonstrated. Don't copy us.Think about each procedure you're going to perform beforehand. Safety First!
6 Popular Woodworking August 2001