Biscuits?

[dcarter636]

Cody, I tend to take those magazine tests with a heap of salt. The anticipated stress modes matter greatly when deciding what joinery to use. They headline STRONGEST JOINTS but rarely do comprehensive comparative testing for shear, peel, tensile, and bending strength which can be different as night and day, as are pressure vs force.

It is usually not so hard to make a few sample joints and evaluate them for good enoughness before making a bunch more. That is a basic practice here when uncertain of a joint or using unfamiliar materials.

[Ruffnek]

Understood, Dave. The test was certainly not all-encompassing but it was a test and unlike tool tests and advertising, there was nothing for FWW to gain by tweaking the results. I reference that test because I haven't found a more reliable source of data on joint strength.

Here's what the article said about the procedure:

Fine Woodworking teamed up with a group of research engineers to test 18 popular frame joints and see which is strongest. We made five sets each of 18 different types of joints in cherry, a species used often by furniture makers. The samples were placed in a servo-hydraulic materials testing machine--essentially a hydraulic ram hooked up to a computer to record force and movement--and broken.

I know biscuit joinery isn't for everyone. I do, however, question absolute statements about the strength of said joint based on nothing but an opinion or speculation. Like I said, the FWW test was likely a lot more in-depth and scientific than any test done by anyone here. If anyone has done a controlled joinery test, then let's hear about it.

Too, Jbark wasn't asking what was the strongest joint he could use. Considering where he's worked and his experience, I imagine he knew the answer to that question. What he wanted to know was if biscuit joinery was strong enough to use on a quick and dirty cabinet door. I think it is and supported my opinion with the FWW test.

BTW, I'd be interested in hearing how many persons here have had a biscuit joint fail and what was the failure condition/mode? There's nothing like case history to shed light on a subject.

[dcarter636]

I spent a bit of time trying to remember biscuit joint failures, they were all many years ago and there was more than one, all were mitered corners but only one is absolutely clear in my memory.

We once had a king size waterbird and the Naugahyde covered cap rails were past tacky so I made new cap rails of red oak. The cap rail was made of ³/₄" stock glued up in the form of a 3¹/₂" x 3" U-channel. Two big L shaped assemblies about 7' x 3 ¹/₂' with biscuited mitered corners at the apex of the L comprised the cap rails that wrapped the top edge of the bed frame sideboards and foot board.
After a number of years of service when removing the caps for some maintenance one mitered L fell apart as I picked it up. The biscuit was unharmed and looked as if it had been starved for glue, which was not likely as I always painted the biscuits and slots with tite-bond at assembly.

I kept and still have the long oak U channel pieces thinking they will be handy for something else someday.

I fairness I have not seen a long grain joint biscuit fail but I have never had a long grain glue joint fail otherwise either. The long joints of the oak U channel incorporated biscuits as alignment devices, they are sound but they would also still be sound without the biscuits.

[Ruffnek]

That's interesting, Dave because part of the holding power of biscuits is that they swell when coated with waterbased glue. That termite barf they are made of soaks up water like a sponge.

I was expecting you to say the biscuit had broken instead of the glue bond failing on it. Perhaps the wood soaked up the glue instead of the biscuit?

[fredbelknap]

I had been using the biscuits that they sell at Lowes. I got some at an auction a year or so ago and they are Lamillo brand.sp They fit a lot more snug in the slot than the one from Lowes. I got several hundred at the auction so that is all I use now.