Mortise and Tenon question

[Richard Heidel]

I've seen many ways to cut mortises and tenons. Is there a rule of thumb about the size? I usually figure on about half the stock thickness for the thickness of the tenon, but what about length?

[charlie b]

Depends on what the joint is intended to do.

1 - alignment only of two joined parts, not intended to keep the parts from pulling apart, then a 1/4 inch stubby would work 2 - alignment AND keeping two parallel parts from moving apart - like shelves then 1/2" and glue would work 3 - #2 AND expanding and contracting WITH the parts the tenon goes into - through tenon, with a wedge or two for insurance 4 - #3 AND knock down/take apart/tighten - like a bench's stretchers - then long through tenon with mortise in the tenon for a big wedge

Also depends on what it might interfere with - a table apron to top of legs for example. You don't two want tenons to a) bump into each other or leave so little material on the mortised part so as to have no strength.

As for the width of the tenon - again it depends on what the joint is intended to do. You've got 6 types of motion to deal with - movement on the x-axis, movement on the y-axis and movement on the z-axis along with rotation about each of the three axis. The size of the shoulders mainly deals with rotation around one or more axis.

Rather than go on just check out

And while your there, if you haven't tried handcut dovetails, have a look at

Hope this helps.

charlie b

[Juergen Hannappel]

To extend the original question to what was probably really meant: How deep to meke the mortise (if non-through)?

[Swingman]

To me the "rule of thumb" for "thickness" has generally been 1/3 the thickness of the stock. IOW, a 1/4" thick tenon in 3/4" stock.

Length, for a non-through tenon, is generally is 1/16th - 3/16th less than the depth of the mortise to allow for the glue.

[Swingman]

I hesitate to read any meaning into what is said ... therein lies the beginning of many a flame fest.

Traditionally the depth of a mortise is about 3/4 the width of the leg or stile.

Depends on a number of things, the size of the workpiece in which the mortise is being cut, the size of your chisel/tools/bit, the stroke of your mortise machine, whether you are using joinery like mitered tenons, etc.

On a 1 3/4 to 2" " table leg, I generally make my mortises about 1" deep ... maybe a little deeper for thicker table legs, or when I want to miter the ends of the opposing tenons.

[Phisherman]

One third to one-half is about right, but consider matching the width of your chisel or router bit. A deeper tenon will provide more gluing surface, and therefore a stronger joint. A short tenon is called a "stub tenon," and can be perfectly fine for applications where strength is not a big concern.

[Jim Wilson]

Don't blame you...

Ah, traditions! (G) I traditionally cut blind mortises between 1/2 and

2/3 the width of a stile or leg, but it really depends more on the application dimensions, as you subsequently noted.

Also, I saw in your first post that you suggested 1/3 stock for tenon thickness. When joints with those dimensions do fail in the wood, it is by tenon fracture, and virtually never by mortise wall failure. (Of course, the vast majority of m/t failures are glue failures.) This suggests that a thicker tenon would lead to a theoretically stronger joint, and so I went to approximately 1/2 stock for tenon width a number of years ago. I can't say I've really notice any difference -- never had a tenon failure before switching, either -- but it does seem to be a sensible change.

I don't intend any of this as a contradiction to your custom, but rather to point out that mortise-and-tenon joinery is tolerant of a fairly wide variance in component dimensions.

Jim

[Swingman]

You're absolutely correct.