[berry]

I'm going to make some cabinet doors soon and in looking over my old magazines it's clear that mortise & tenon joints are preferred.

My question is why not use biscuit joinery?

 

[bobj3]

Hi Berry

"My question is why not use biscuit joinery?"

Because we all have kids that get mad sometimes and the biscuit can't take it.
It's just a butt to butt joint so to speak with a spline that holds it as one.
Once the glue joint moves that's it,and it's going to fail, unlike mortise & tenon, it's hard to break the glue joint,because of the size and the amt.of glue use on this type of joint.

Bj

 

[Mike]

Berry, biscuit joinery actually is a mortise and floating tenon joint. The reason conventional mortise and tenon joints are prefered for door frames is strength. When building the doors you want as much material as possible involved in the joint to reduce the likelihood of the door sagging or joint failure. It helps to think of wood as a bundle of straws held tightly together. Glue adheres well to grains running in the same direction or at right angles to each other like in plywood. End grain does not offer enough purchase for the glue to hold. Anything we do to increase the amount of glue surfaces makes the joint stronger. A butt joint has one glue surface. Changing this to a rabbited joint gives 3 glue surfaces. A half lap joint also offers 3 glue surfaces but with a much larger area hence stronger. A through tenon offers 4 surfaces and a regular mortise and tenon offers 6 glue surfaces. This is the reason you see stacked biscuit joints for added strength, 7 glue surfaces but a much smaller area. Needless to say, solid wood is stronger than glueing a biscuit across the grain, and this is why conventional mortise and tenon is preferred..

 

[Woodnut65]

Hi Berry, Mike has given good info. Mortise and tenon joinery is a preferred method.
The joints can be made with a router to give a number of profiles on the stiles and rails. These are also made with a shaper, usually in a production shop. If you use a conventional mortise and tenon the stiles and rails are left square. Hope this helps.
Woodnut65

 

[vaking]

I have seen an article in one of woodworking magazines (don't remember which) that compared strength of biscuit joint against M&T in some practical test. Biscuit joint proved itself reasonably strong at the beginning, slightly weaker than M&T but not by much. The major difference turned out to be at how the joints fall apart. M&T starts slowly to give up as the load increases. Biscuit, as opposed to it, reaches certain point and then falls apart completely at once. In other words, M&T dies gracefully while biscuit just quits on you. The door built with M&T over time may start saging and cracking but biscuit door you will just find on the floor in many separate parts one day.