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Which joint is stronger?

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Forum topic by MrRon posted 02-15-2019 08:14 PM 735 views 0 times favorited 22 replies Add to Favorites Watch
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MrRon

5364 posts in 3541 days


02-15-2019 08:14 PM


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.


22 replies so far

View bmerrill's profile

bmerrill

46 posts in 371 days


#1 posted 02-15-2019 08:58 PM

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

-- "Do. Or do not. There is no try". Yoda

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pottz

4462 posts in 1282 days


#2 posted 02-16-2019 12:34 AM

of the two id go with the top example.

-- sawdust the bigger the pile the bigger my smile-larry,so cal.

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jdmaher

446 posts in 2877 days


#3 posted 02-16-2019 12:35 AM

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

-- Jim Maher, Illinois

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BFamous

299 posts in 418 days


#4 posted 02-16-2019 01:13 AM

Yep, top… Rule of 3rds.

-- Brian Famous :: Charlotte, NC :: http://www.FamousArtisan.com

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waho6o9

8593 posts in 2874 days


#5 posted 02-16-2019 01:20 AM

Top one

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pintodeluxe

5883 posts in 3111 days


#6 posted 02-16-2019 01:27 AM

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

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

View TungOil's profile

TungOil

1143 posts in 792 days


#7 posted 02-16-2019 02:28 AM

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

-- The optimist says "the glass is half full". The pessimist says "the glass is half empty". The engineer says "the glass is twice as big as it needs to be"

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MrRon

5364 posts in 3541 days


#8 posted 02-16-2019 06:14 PM

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

1143 posts in 792 days


#9 posted 02-16-2019 06:44 PM



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.

-- The optimist says "the glass is half full". The pessimist says "the glass is half empty". The engineer says "the glass is twice as big as it needs to be"

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John_

197 posts in 2003 days


#10 posted 02-16-2019 07:47 PM

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

2197 posts in 872 days


#11 posted 02-16-2019 07:50 PM

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.

-- Think safe, be safe

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runswithscissors

2987 posts in 2323 days


#12 posted 02-16-2019 10:23 PM

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

-- I admit to being an adrenaline junky; fortunately, I'm very easily frightened

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MrRon

5364 posts in 3541 days


#13 posted 02-17-2019 12:04 AM

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?

View pottz's profile

pottz

4462 posts in 1282 days


#14 posted 02-17-2019 12:27 AM

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!.

-- sawdust the bigger the pile the bigger my smile-larry,so cal.

View Richard's profile

Richard

11213 posts in 3330 days


#15 posted 02-17-2019 12:45 AM



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!

-- Richard (Ontario, CANADA)

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