Three sided tenon

[dvan1901]

I recently watched a video of a shaker style table build and I was pleasantly surprised to see they also used a 3 sided tenon; meaning that the back of the tenon was flat so only the top, bottom and face side were milled. I have done this on a couple of projects and wondered about it and decided that it does not compromise the strength of the joint at all, but in fact allows the joint to be stronger. I am interested in hearing what other people think about this.

For example, let's say you are making a side table in which the legs are 1.5" square and you need to put a 3/4" mortise/tenon into them and you want the rails to be flush with the face of the legs. Well, if you follow the general principle that the tenon should be half of the thickness of the rail, then you have a 3/8" tenon. The problem is, that means you have only 3/16" from the face of the leg to the mortise, which is not a lot of room and could be a very weak joint. However, if you use a 3 sided tenon, you can then make the tenon the same 3/8" thick, which then lets you make the mortise 3/8" back from the face of the leg, which gives you more strength. Or, you could use a 1/2" tenon and set it back a 1/4" and will still give you a good bit of strength. Make sense? I'm still learning so I would love to hear other peoples thoughts.....

[Pete Bennett]

I recently watched a video of a shaker style table build and I was pleasantly surprised to see they also used a 3 sided tenon; meaning that the back of the tenon was flat so only the top, bottom and face side were milled. I have done this on a couple of projects and wondered about it and decided that it does not compromise the strength of the joint at all, but in fact allows the joint to be stronger. I am interested in hearing what other people think about this.

For example, let's say you are making a side table in which the legs are 1.5" square and you need to put a 3/4" mortise/tenon into them and you want the rails to be flush with the face of the legs. Well, if you follow the general principle that the tenon should be half of the thickness of the rail, then you have a 3/8" tenon. The problem is, that means you have only 3/16" from the face of the leg to the mortise, which is not a lot of room and could be a very weak joint. However, if you use a 3 sided tenon, you can then make the tenon the same 3/8" thick, which then lets you make the mortise 3/8" back from the face of the leg, which gives you more strength. Or, you could use a 1/2" tenon and set it back a 1/4" and will still give you a good bit of strength. Make sense? I'm still learning so I would love to hear other peoples thoughts.....

For a while there I was confused by what you meant by a three sided tenon.

The technical term for what you are describing is 'A Bare Faced Tenon' and they are very common. Like you say they sometimes mean a stronger joint and infact are used for exactly that reason in situations such as the one you describe.

To do a good job though you have be to more accurate and careful in your setting out and making the mortice. Any slackness and you do not have a convenient shoulder to hide the oversized mortice.

Pete

[flairwoodworks]

I recently watched a video of a shaker style table build and I was pleasantly surprised to see they also used a 3 sided tenon; meaning that the back of the tenon was flat so only the top, bottom and face side were milled. I have done this on a couple of projects and wondered about it and decided that it does not compromise the strength of the joint at all, but in fact allows the joint to be stronger. I am interested in hearing what other people think about this.

For example, let's say you are making a side table in which the legs are 1.5" square and you need to put a 3/4" mortise/tenon into them and you want the rails to be flush with the face of the legs. Well, if you follow the general principle that the tenon should be half of the thickness of the rail, then you have a 3/8" tenon. The problem is, that means you have only 3/16" from the face of the leg to the mortise, which is not a lot of room and could be a very weak joint. However, if you use a 3 sided tenon, you can then make the tenon the same 3/8" thick, which then lets you make the mortise 3/8" back from the face of the leg, which gives you more strength. Or, you could use a 1/2" tenon and set it back a 1/4" and will still give you a good bit of strength. Make sense? I'm still learning so I would love to hear other peoples thoughts.....

In other words, the tenon only has three shoulders. Gotcha. Makes sense if that's your application. I've never had an occasion to set rails/aprons flush with the legs - I always inset them.

[dvan1901]

In other words, the tenon only has three shoulders. Gotcha. Makes sense if that's your application. I've never had an occasion to set rails/aprons flush with the legs - I always inset them.

When I built this coffee table, I had the rails flush to the legs so this came in handy

[Pete Bennett]

Nice table but, and I really do hate criticising other's work, but if it had been me I would have made the apron frame slightly smaller to allow for a bit more overhang of the top and I would have given the knees of the cabrioles a little more radius to make them flow better into the lower leg section. Only my opinion mind. I'm sure your wife loves it just the way it is.

Pete