# Mortise and Tenon sizing question



## Bugzy (Jul 15, 2014)

Hey everyone,

Looking for a little expert or experienced advise on mortise and tenon sizing for a Oak table I'm making.
I'm relatively new to larger furniture pieces with a couple beds, fire wood rack, hall tree and a dresser under my belt with what i call great success.

Most of these items consisted of glue up, pocket hole joinery and detail work with a router etc….

I'm in the midst of building an Oak table that is 36" x 76" 1.75" glue up top with 3.25" square birch legs with a 1/2" taper on two sides (shaker style).

The issue i am having which is from my ZERO experience with mortise and tenons is the apron and leg interface.
Currently i have 3/4" Oak dressed on all 4 sides for a 3.5" high apron. From all the reading and previous forum topics they suggest 1/3 the woods thickness for the tenon size which would mean my tenon would only be 1/4" thick which does not seem "beefy" enough for such a heavy table top.

If i made the tenon 1/2" with 1/8" shoulders(?) is that an issue? 
Have i screwed up by assuming the 3/4" apron thickness is enough to carry this load and still provide the stability needed?
Disclaimer: I was sourcing some unfinished 5/4 poplar for this but was guided to the 3/4" D4 Oak by the shop. Their was a lot of waste in the 5/4 that was available so it would have been spending the same +/- in the end and saved me some work.

I hope i have been clear in the above, and looking forward to hearing your point of views

Cheers,


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## HerbC (Jul 28, 2010)

With 3/4" thick aprons, 1/4" thick tendons would normally be correct.

Herb


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## jmartel (Jul 6, 2012)

If you increase the tenon size, you decrease the wall size. 1/3 is a good general guideline.


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## jdh122 (Sep 8, 2010)

The 1/3 rule only applies when your mortise material is the same thickness as the tenon material. With legs at over 3 inches you're going to have over an inch wall thickness on the mortises no matter what, so make the tenons as thick as you can, since that's what's going to determine the strength of the assembly. You want to have some shoulders on the tenon to hide the joint, but 1/8th inch would be plenty. In fact I'd probably only do a shoulder on the front of the aprons, which would mean that the tenon would be 3/4-1/8=5/8.


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## TheFridge (May 1, 2014)

Where the legs are thicker I usually leave enough to where my dovetail saw won't break out the edge. I make the tenon as large as possible.


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## pintodeluxe (Sep 12, 2010)

1+ with Jeremy and thefridge above… the 1/3 rule doesn't apply here. 
Shoot for 1/2" thick tenons. Shouldered tenons not only hide the joint, but help resist racking forces.


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## Bugzy (Jul 15, 2014)

LJ's come through in a pinch again!!!

Jeremy- eliminating the back shoulder and only providing a front giving me a 5/8" tenon sounds like a great idea.
Appreciate the advice and help everyone….... now to butcher some scrap wood perfecting this!

Thanks again everyone.


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## jdh122 (Sep 8, 2010)

Pintodeluxe's point is a good one, namely that the shoulders actually add strength. Might be better to put at least a tiny shoulder on the back too…


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## Kirk650 (May 8, 2016)

Heck, I'd have used 3/8 inch tenons. That or the 1/4 inch.


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## MadMark (Jun 3, 2014)

Ideally, the strongest M&T is where both have equal wood. This suggests the natural ratio of 1/4:1/2:1/4. This is also the same spacing ratio for hole drilling, hinge spacing, clamp spacing and the like.
M


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## rwe2156 (May 7, 2014)

For 3/4 material I typically use 3/8 -1/2 thick tenons. The shoulders are what really give the joint its strength so I make the bottom shoulder 3/4 - 1".

On a separate note, I'm wondering if 3/4" X 3 1/2" aprons are beefy enough for a top that thick. I would go with 1 1/4" material with 3/4" tenons.

Also, pinning the tenons adds a huge amount of strength.


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