Mortise and Tenon sizing question

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Forum topic by Bugzy posted 06-20-2016 03:13 PM 474 views 0 times favorited 10 replies Add to Favorites Watch
View Bugzy's profile


10 posts in 833 days

06-20-2016 03:13 PM

Topic tags/keywords: apron mortise and tenon table

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


10 replies so far

View HerbC's profile


1568 posts in 2280 days

#1 posted 06-20-2016 03:24 PM

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


-- Herb, Florida - Here's why I close most messages with "Be Careful!"

View jmartel's profile


6469 posts in 1571 days

#2 posted 06-20-2016 03:26 PM

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

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

View jdh122's profile


878 posts in 2239 days

#3 posted 06-20-2016 04:09 PM

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.

-- Jeremy, in the Acadian forests

View TheFridge's profile


5676 posts in 907 days

#4 posted 06-20-2016 04:29 PM

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.

-- Shooting down the walls of heartache. Bang bang. I am. The warrior.

View pintodeluxe's profile


4825 posts in 2234 days

#5 posted 06-20-2016 07:04 PM

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.

-- Willie, Washington "If You Choose Not To Decide, You Still Have Made a Choice" - Rush

View Bugzy's profile


10 posts in 833 days

#6 posted 06-20-2016 07:10 PM

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.

View jdh122's profile


878 posts in 2239 days

#7 posted 06-20-2016 07:22 PM

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…

-- Jeremy, in the Acadian forests

View Kirk650's profile


272 posts in 170 days

#8 posted 06-20-2016 08:58 PM

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

View MadMark's profile


968 posts in 874 days

#9 posted 06-20-2016 09:30 PM

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.

-- Madmark -

View rwe2156's profile


2119 posts in 902 days

#10 posted 06-21-2016 12:15 PM

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.

-- Everything is a prototype thats why its one of a kind!!

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