| Rumpty wrote:
| > >I don't know that I'd bother with the bisquits Mike. They make
| > easier, but they don't strengthen the joint.
| > It's a shame this myth continues on the wreck. Many a great kitchen
| > has been built with biscuits and they haven't fallen off the wall.
| If one
| > takes time, you will learn biscuits are a wonderful tool to use in
| > woodworking, and they easily perform structural tasks.
| Nobody is saying biscuits are useless, but just because the cabinet
| hasn't fallen off of the wall doesn't mean they strengthen the joint
| (depending on the joint).
| Certainly a biscuited right angle joint would be stronger than a butt
| joint, but I'd like to hear the science of how a biscuited edge joint
| would be stronger than a non-biscuited edge joint.
This may not please you, but; a biscuit seems to me to be of about the same value to a joint as a floating tenon in that it will serve to increase the glue area thereby increasing the durability and stability of the joint.
That said, the actual durability of the joint would seem to be dependant upon the quality of the glue and glue-up, and the drying time. Issue 157 of WOOD (Sept 2004) has a comparison of various glues - polyurethanes, PVA's and water-resistant PVA's. The following tests used only but joints with no additional reinforcment. All the glues tested seemed to achieve maximum strength after 30 minutes of drying time except for the polyurethanes which required 120 minutes.
When joining edge grain to edge grain, almost all the glues tried resulted in the wood failing before the glued joint. The pressure required to "break" the joint exceeded 1600 PSI in all cases. In this instance, a tenon of any variety would seem superfluous.
When gluing edge grain to end grain, the results are quite different. The use of a tenon/biscuit, dowels, cope and stick is highly recommended.
The polyurethane glues failed between 350PSI and 800PSI, the water-resistant PVA's failed between 1200PSI and 1800PSI, and the PVS'a failed between 1150 PSI and 1400PSI. Of note is the fact that 4 glues surpassed all others in this area (the wood failed before the glue). These glues are:
Elmer's Carpenter's ProBond Interior/Exterior
Titebond Moulding and Trim
Loctite Professional Wood Worx
Elmer's Probond Interior