Dado vs. Mortise and Tenon

[Dan Barr]

Wouldnt the Dado be stronger since it has much more gluing surface?

any opinions?

thanks,

dan

[Thom Sturgill]

Wouldn't that depend on the application? I think the greater depth of a mortise and tenon would be needed for a leg/skirt connection while it would be overkill for a shelf and a dado would be appropriate. Also would it not depend on the DIRECTION of the stresses ?

[Jim Becker]

Well...in a sense, putting any portion of one board into a groove/dado/rebate is kinda similar to an M&T joint. :)

That said, Thom is correct...your specific application needs to be considered including the use/stresses applied and in what direction. A shallow M&T joint is very similar to a tongue/groove joint or material inserted into a groove/dado/rebate. A traditional M&T joint, depending on the size could easily exceed the glue surface area of the other methods or be similar.

[Jake Helmboldt]

Apples to oranges; as Thom mentioned it really is an issue of application. A dado and M&T really don't have the same application/purpose (though I suppose there would be instances).

But the M&T I think would be regarded as much stronger in general unless it is a little stub tennon. A dry-fit M&T joint can hold itself together without glue; you actually need to work to get the joint apart when you go to glue it together. But you won't see the same with dados because they are so shallow.

As for application, again they really serve different purposes.

[Danny Thompson]

Remember, it is long grain-to-long grain gluing surface area that matters. Many Dado joints result in very little long-to-long. If you have end grain sitting in your dado, you only get to count the shallow dado walls, but not the wide "floor" of the dado (because it has end grain against it). With M&T you typically get to count all four walls of one mortise and the 2 long walls of the other. If the dado has long grain along the floor, then it's a different story.

[Dan Barr]

im going to make a frame and panel.

wouldnt a 1/2" deep dado for the ply be plenty strong? these frame and panels will be the sides and front of a desk and the legs of the desk will be the stile. i dont think im going to need tenons on the rails since ive got the dado running the whole way around.

(See attached Powerpoint slide)

let me know what you all think,

thanks,

dan

[Jim Becker]

Frame and panel are typically made with cope (effectively tongue and groove) joints. They are sometimes made stronger with haunched tenons, especially if they are large or supporting weight as yours will be if the legs are integral with the panels.

[Danny Thompson]

Wait. So how are the rails joined to the legs? It would be normal to have a mortise on the end of the rails sitting in the dado of the legs. The dado would stop at the bottom of the tenon.

This is how I made the frame and panel on my footboard. See the bottom rail tenon sits in the leg dado, as does the panel.

[Dan Barr]

This is what im thinking.

My assembly is pretty much like yours. since the dado is so long and has plenty of surface area, i wont need the mortise and tenons for the rails. the dado will hold them in place. i can just put a couple of pocket screws in the rear of the rail if this is not sufficient.

thanks,

dan

[George Bregar]

This vanity uses both frame and rail and mortise and tenon joinery. The leg has a dado to accept the panel, and mortises for the tenons on the rails. I would do the same for your desk, but of course, it's up to you. The M&T will resist the racking that a desk will have. A frame and rail will not...well not as well...and pocket screws will fail over time too.

[Danny Thompson]

Dan,

So, the rail will not sit in the dado, right? The panel will be the only thing in the dado and the bottom rail will, essentially, be a piece of decorative trim glued to the bottom edge of the panel. Initially, the rail will not be secured to the legs, and it will not provide any support for the pane. Later, if you decide that you need more support, you can pocket hole the bottom rail to the legs.

OK, I can buy that and think you would be okay. Not traditional, but I think it would work fine, assuming you do not expect any outward pressure on the rail. If you are using this type construction for a door, then make sure the bottom rail doesn't provide a touchpoint with the face of the cab.