Thru mortise and tennon on wide board?

[harry boyer]

I'm making a bench seat with 15" wide 6/4 cherry. I'm concerned about expansion and contraction . The top would be mortised at the top of the leg with about a 2" over hang on each side. The leg is mortised to a stretcher running between the legs with 1/2"x 1" tennon 1" deep . I've seen thru mortise and tennons on benches but I'm wondering if it is safe long term. I'd hate to see the top pull the sides apart. I'm also thinking figure 8 type table top attachment.

Your imput is valued!

[Philip Rodriquez]

You can make the mortise a little longer and only glue in about 5" of the tennon. Just remember to glue in the section you want to stay put!

[Rich Enders]

I recently built a series of similar WO benches with M&T construction similar to what you described. I did not glue the M&T joints in the leg to stretcher connection just below the seat. I can let you know in a few years how they hold up...

[Kent A Bathurst]

I'm making a bench seat with 15" wide 6/4 cherry. I'm concerned about expansion and contraction . The top would be mortised at the top of the leg with about a 2" over hang on each side. The leg is mortised to a stretcher running between the legs with 1/2"x 1" tennon 1" deep . I've seen thru mortise and tennons on benches but I'm wondering if it is safe long term. I'd hate to see the top pull the sides apart. I'm also thinking figure 8 type table top attachment.

Your imput is valued!

I'm not sure I understand "top would be mortised at the top of the leg" - you mean the legs will have tenons that go into the bench seat/top? That might cause a problem, as you apparently are thinking about. You are thinking correctly in terms of the top moving when the stretcher/rail won't. OTOH - I don't know how much of a problem you would actually see - 15" less 2" overhang on both sides = 11" of actual wood to worry about movement - could be fine - flip a coin.

The other option - forget the leg's tenons into the top's mortises - Use figure-8 or use "z-clips" - aka "offset fasteners" [photo]. I use both, but I like the z-clips better...You can cut a saw kerf along the top inside of the rail before you assemble it, then these clips fit into those kerfs, and you screw into the top. Holds very tight, and still lets the top move.


http://www.highlandwoodworking.com/ProductImages/hardware/188105.jpg