# Mortise and tenon rule of thumb?



## KenBry (Sep 13, 2011)

I am getting ready to create several mortise and tenon joints. I was wondering if there was a "rule of thumb" when cutting these.
So for inctence my 4.5" rails are going across a 20" distance into 2" square legs. The rails are 3/4" thick. The question is what should my tenon dimensions be? I know once I have my tenon dimensions I can cut my mortise first then cut my tenons to fit tight. I also know I need extra material on the ends to allow for the tenons just not sure how much I should have.


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## crank49 (Apr 7, 2010)

Most rules or reccomendations I have seen suggest 1/3 the stock thickness. So, for 3/4" stock that would be 1/4". I agree with that and thats what I use for 3/4" into another 3/4" piece. In your situation, 3/4" into 2" stock, I would make my Tennon 3/8" or maybe even 1/2" if it needed extra strength; like for a long rail.

I try to make the length of my tennons 2 times their width. So, if you go 3/8" tennon, they would be 3/4" long. Again, this can change depending on the application. Like for pinned tennons, they have to be longer.

Note that if you have 1/2" tennons on two sides of a 2" leg and make them both 1" long, the ends will have to be mitered.


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## Rick Dennington (Aug 27, 2009)

I agree with crank49 on his explanation of what needs to be done to mortise and tenons…..That's pretty much how I do all of mine with the stock you mentioned. Most of the time when I work with 3/4" stock, I normally do the 1/4" mortise and tenons…...One thing I've found….when I make the tenons 1" long, I usually have to shave them back to about 7/8",or a shade shorter to keep them from hitting each other… Sorry…I see that crank has already explaned that…..


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## Loren (May 30, 2008)

1/2 to 1/3 the stock thickness.


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## KenBry (Sep 13, 2011)

Thanks for the help folks. Based off the recomendations I am going to make my tenons 3/4" long and 3/8" wide. For this project.


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## RGtools (Feb 18, 2011)

I know this is a late entry and I agree with all of the above but would like to add:

The rule I use is to equalize the strength of the two peices. On 3/4 stock a good tenon width is 1/4, length 1 and 1/4 long if you can make that happen….but this is a rule for joining equal width peices. If you are joining a 3/4 peice of material into the face of some stock 3 inches wide, making the tenon thicker will increase the overal strength of the joint.

You should also factor in how you cut your mortise (for me, what size chisel I have on hand) and match your width to the closest tool you have on hand. I also factor the strength of the woods being joined, if I am putting hickory into poplar for instance, the tenon can be slimmer to equalize the strength of the peice.


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## Rick Dennington (Aug 27, 2009)

RGtools….....I'll buy that for a dollar…..


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