# Which joint is stronger?



## MrRon (Jul 9, 2009)

This is a simple M&T joint that is glued. I'm guessing that they are equal in strength. This joint would be typical for a stretcher between two legs.


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## bmerrill (Mar 14, 2018)

Rule of thirds. 1st one has the proper measurements for 3/4" stock.


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## pottz (Sep 15, 2015)

of the two id go with the top example.


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## jdmaher (May 4, 2011)

First one (1/4" tenon) is stronger. On the second (3/8" tenon), sides of the mortise are weaker.


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## BFamous (Jan 26, 2018)

Yep, top… Rule of 3rds.


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## waho6o9 (May 6, 2011)

Top one


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## pintodeluxe (Sep 12, 2010)

5/16" thick tenons work well on 3/4" stock as well.


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## TungOil (Jan 16, 2017)

I agree with Willie, 5/16" tenon is a good choice for 3/4" thick material.


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## MrRon (Jul 9, 2009)

What if the piece receiving the mortise were 1-1/2" thick and the piece with the tenon was 3/4" thick; assuming the mortise is centered. Then I assume the thicker the tenon, the stronger it will be. Maybe even eliminate the tenon altogether and cut a 3/4" mortise. The rule of 3rds would dictate that the tenon be 1/2" thick.


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## TungOil (Jan 16, 2017)

> What if the piece receiving the mortise were 1-1/2" thick and the piece with the tenon was 3/4" thick; assuming the mortise is centered. Then I assume the thicker the tenon, the stronger it will be. Maybe even eliminate the tenon altogether and cut a 3/4" mortise. The rule of 3rds would dictate that the tenon be 1/2" thick.
> 
> - MrRon


In that situation I'd probably use a 3/8" or maybe a 1/2" tenon to allow for some shoulders around the tenon. Really depends on the application.


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## John_ (Sep 23, 2013)

Opinions vary greatly on this. Here are the 'general rules' that I go by regarding the thickness and width of a tenon. I don't remember where I got this from, but I keep things like this in OneNote (electronic notebook) for easy reference

Note, the first rule applies directly to your diagram. If your hand cutting the tennons you would use 1/3, if your machine cutting them you would use 1/2










and here is a simple chart


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## therealSteveN (Oct 29, 2016)

Thirds for same same wood both sides. I've seen some pretty respectable folks who would use #2 example if the tenon was poplar, pine, something softer, going into something really hard.

To your second part, yes the thirds could flex with thicker pieces, but math is easier at thirds, so it often wins. Plus what I said about even 3/4" still can apply. I have seen a perfectly mortised piece with 1 1/2" x 3/4" parts where there was no shoulder, direct placement. Rules are made to be broken, or at least bent a little.

"Really depends on the application" that statement right there really drives the bus.


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## runswithscissors (Nov 8, 2012)

Another vote for 5/16" tenons with 3/4" stock. The tenon is a lot stronger, walls of mortise still plenty strong.


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## MrRon (Jul 9, 2009)

It seems there are several different opinions here, so I will go with the 3/8" tenon in 3/4" thick stock (2nd sketch). The reason why I come up with this is there is an equal amount of cross section in both pieces. You have 3/8" for the tenon and 3/16" x 2 = 3/8" total meat on the mortise end. If you go by the 3rd's rule, you will have 1/4" meat on the tenon end and 1/4" x 2 = 1/2" meat on the mortise end. My reasoning is, an equal amount of wood is removed from each end. Does that make sense?


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## pottz (Sep 15, 2015)

here we go again with overthinking common sense and logic,cmon guys really!were not sending rockets to mars here,for gods sake.ron go with the top one and you'll live to see tomorrow and your project will out live you and your grand kids-LOL!.


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## Magnum (Feb 5, 2010)

> here we go again with overthinking common sense and logic,cmon guys really!were not sending rockets to mars here,for gods sake.ron go with the top one and you ll live to see tomorrow and your project will out live you and your grand kids-LOL!.
> 
> - pottz


Sounds good to me! Enough Is Enough! Thanks Pottz!


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## MrRon (Jul 9, 2009)

I am a retired engineer, not the railroad kind, and being an engineer makes me want to question everything.


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## MNgary (Oct 13, 2011)

Are you asking for lateral strength or rotational resistance?


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## MrRon (Jul 9, 2009)

This is the actual joint I'm making for my tool stand. This shows one leg and 2 stretchers.


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## bondogaposis (Dec 18, 2011)

One thing you are not thinking about is racking. The 1/4" tenons provide greater bearing surface on the shoulders of the joint. It is the shoulders of a M&T joint that prevent racking. A table apron can take a lot of racking force because of the leverage that can be applied by the length of the leg. If it was mine I'd go with the 1/4" tenons.


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## MrRon (Jul 9, 2009)

> One thing you are not thinking about is racking. The 1/4" tenons provide greater bearing surface on the shoulders of the joint. It is the shoulders of a M&T joint that prevent racking. A table apron can take a lot of racking force because of the leverage that can be applied by the length of the leg. If it was mine I d go with the 1/4" tenons.
> 
> - bondogaposis


I hear what you are saying. I don't expect any racking in my stand as all forces imposed on the stand will be in a vertical direction. If this were a tool that would require me to apply horizontal force, then racking would be a big factor. A scroll saw would impose minimal horizontal force. I could have made the stand as a box using plywood, but I feel an open leg design is adequate for my purpose.


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## wormil (Nov 19, 2011)

> One thing you are not thinking about is racking. The 1/4" tenons provide greater bearing surface on the shoulders of the joint. It is the shoulders of a M&T joint that prevent racking. A table apron can take a lot of racking force because of the leverage that can be applied by the length of the leg. If it was mine I d go with the 1/4" tenons.
> 
> - bondogaposis


Bondo for the win. 
Shoulders are as important at the tenon.


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## LesB (Dec 21, 2008)

For holding a stretcher in place I would expect either joint to do the job.


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