Mortise & Tenon - 2x4 into a 4x4

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Forum topic by AwlThat posted 02-05-2019 03:59 PM 3435 views 0 times favorited 3 replies Add to Favorites Watch
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55 posts in 969 days

02-05-2019 03:59 PM

I’ve read where a good standard for figuring the size of a tenon is that it should be 1/3 the thickness of the work piece.

If I do that with a 2×4, which is actually only 1.5”, then I’d have 1/2” shoulders and a 1/2” thick tenon.

Is that sufficient or should I have 3/8” shoulders with a 3/4” tenon? Or are the 3/8” shoulders insufficient?

The length of the tenon is intended to be 2”.

The project is a workbench base, supporting a Paulk-style top.

I certainly don’t expect this workbench to have to bear tremendous weight on a regular basis, I just want to use mortise & tenon joinery for this project.

3 replies so far

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9073 posts in 3033 days

#1 posted 02-05-2019 04:13 PM

Either one is fine. You should have plenty of bearing surface to hold up weight.

-- The quality of one's woodworking is directly related to the amount of flannel worn.

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257 posts in 2587 days

#2 posted 02-05-2019 06:30 PM

The risk you run if your tenon is too thin is outside wall break through. I use hand tools ,so I chisel out tenons, so if I am too close to the mortice wall If I am not careful when wedging out the waste I can crack the mortise wall. The 1/3 rule is base mostly on that premise because you are more likely to break the mortise side than you are to break the tenon.

-- "The pursuit of perfection often yields excellence"

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55 posts in 969 days

#3 posted 02-05-2019 06:52 PM

Thank you both for the replies.

You make a great point, oltexasboy1. It is especially relevant to what I intend to do.

The design I’m working on is a 5’ x 3’ workbench. It will have 3 4×4’s down each side, one on each corner and one in the middle. I will have the 2×4 rails flush with the outside of the 4×4 legs, which leaves either 1/2” of outer wall if I go with a 1/2” tenon or only 3/8” if I do a 3/4” tenon.

If I center the tenons on the legs, to allow for more of a mortise wall, then the tenon’s can’t be 2”. On a corner, for example, a 1/2” tenon only allows for a 1 1/2” tenon length. I could miter the tenons and get 1 3/4” but that’s the max.

I could offset the tenons from the center by 1/2” and that would leave an inch of wall for the mortise and allow for a 2” tenon length, without mitering the tenons. That idea assumes a 1/2” tenon thickness.

I love how talking through something can bring out more ideas. Thanks, fellas.

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