Haunched tenon?

[Andrew Gibson]

I have a tenon question. What is the purpose of the Haunch on a Haunched tenon?
I generally see these used when attacking a skirt board or the like to a table leg. I have just not figured out what makes these desirable over a plain tenon.

Fig-130-Haunched-Tenon-used-at-end-of-Door-Frame.jpg

[Sean Hughto]

It makes the joint stronger and more rigid. It effectively gives you a wider tenon at the weakest - least supported point of the joint - thus allowing the cross member to better resist twisting and generally sustain heavier loads. In a rail and stile door, the ahunch fills the groove cut for the panel.

[Andrew Gibson]

Thanks Sean. I have been thinking about this for about 2 weeks while planning a project, and I just was not wrapping my head around the concept for some reason.

[Lex Boegen]

The haunched tenon provides the benefit of a wide tenon in regards to preventing twisting, but without the additional problem of wood movement in a cross-grain situation. This is why very wide tenons (like a headboard) are always broken down into two or more tenons.

[george wilson]

The haunched tenons I have used do not terminate in a little angled off section as illustrated. My choice is the type that goes into the mortise straight,then is cut off at 90º. Say your tenon is 3" deep,the haunched part might be 1" or so deep. This type gives twice the glue area than the triangular one.

[Brett Bobo]

Just to be sure I'm understanding the responses correctly, the purpose of the haunched tenon would either be to clear an obstruction, such as a panel in the rails and stiles, or to prevent cross-grain movement on wider tenons, correct? Otherwise, a traditional (non-haunched) tenon would provide the most stability and strength. In other words, the preference would always be a traditional tenon, if applicable.

[Sean Hughto]

No, I don't think you've got it.

A haunch is often used in frame a panel doors to fill the groove that was cut for the panel to fit into, i.e., because the groove is not stopped, it must be filled at the top and bottom of the door or you see it as a square hole when the door is glued up.

I haunch is used in post and beam type construction because the wider base of the tenon, means it is effectively stronger and can support more weight on the beam. It is also somewhat more rigid as the broader base of the tenon resists twisting.

The haunch also helps in door construction because door to rooms and houses take lots of stresses - the broader base of the tenon provides more strength and rigidity. Using only a haunch is useful in this application rather than just a bigger tenon, becuase the narrower tenon further into the mortise makes breakout of the mortise at the end grain less likely (there is more wood between the edge of the tenon and the top or bottom of the door rendering the mortise more durable).

[Frank Drew]

IMO the important reason to haunch some tenons, such as those on table rails, top and bottom door rails, etc., is so the full depth mortise isn't at open at the end of the leg or stile once they're trimmed to final length -- that would considerably weaken the joint; when you make a door or table you usually leave the stiles or legs an inch or so long before gluing up, then later cut them flush with the rails; you don't want to expose the full mortise when you do that, so you've shortened the tenon to just a stub for maybe a quarter or a bit more of its width, and the haunch to keep that bit of rail without a full tenon from twisting (that's why you don't cut that portion of the tenon off entirely.)

There's no reason to haunch the bottom of the tenon on a table rail (although you might cut it back entirely a slight bit so that the mortise doesn't come to the edge of the rail where it might show), just as there's no reason to haunch the inner tenon edges on door top and bottom rails, or the tenons on the lock rail.

[Russell Sansom]

If the mortise is narrow and deep, shortening part of the tenon saves considerable mortise chopping and fitting. I don't think so much about gluing area...to my way of thinking the glue doesn't hold a tenon in a mortise, it just fills the voids and helps keep the joint from wiggling loose. The "added" haunch offers better resistance to twisting and greater surface area for getting the rails and styles in the same plane. And as people have mentioned, tenons have to be haunched on a table apron because they have to overlap inside the leg.
I've never been a fan of the mitered tenons meeting in the middle of the leg...it seems to me that there just isn't enough tenon length.

[Brett Bobo]

Sean,
Thanks--I follow what you're saying. My point was that over the length of a tenon, a full-height tenon would be stiffer or more rigid than a haunched tenon at the shallower section. Generally speaking, a 2x6 is obviously stronger, stiffer, more rigid, etc. than a 2x4 of the same grade.

[Sean Hughto]

Brett, I don't want to take on any mantle of authority here - we're just guys talking woodworking and trying to explain our thoughts to one another. Anyway, I drew this quick sketch to explain my thoughts better perhaps. In the end, I think we are in agreement?

[Brett Bobo]

Complete agreement, thanks for clarifying with the sketch! Now, you just need to post a video, similiar to your helpful bowl turning video, to show me how to create the angled, haunched tenon and mortise. Is that the way you make them?

[David Keller NC]

Brett - A very slightly different take based on examining antiques. In my opinion, the reason for haunched tenons has mostly to do with ease of construction with hand tools, and very little to do with the strength of the resulting joint. Specifically, and as Sean and Russell mention, one always would wish to avoid having to cut a stopped groove, because they're way, way more labor to make than a through-groove along the edge of a board. One similarly would like to avoid having to leave a table leg or a stile on a frame & panel door really long to avoid having a sharp whack with a mortise chisel blow out the end-grain on the top of the leg, because leaving somethign extra-long wastes material.

Obviously, cutting a stopped versus a through-groove makes very little difference if one is using a plunge router, and blowing out end-grain on a table leg or a stile isn't an issue with a mortising machine.

On antique furniture from the age of handwork (primarily from before 1830 -1840), one doesn't typically see the angled haunched tenon in your diagram - it would be much more difficult to fit something like that rather than a 90 degree haunched tenon. The 90 degree types, however, are extremely common, particularly on frame and panel doors.

[Brett Bobo]

David,
Thanks for your input. Considering that I'm just now venturing into the world of hand tools, I think that may have been where some of the disconnect came from, e.g. chopping mortises by hand to where the end grain has the potential of blowing out if there's not a substantial amount of wood remaining behind the cut. Using that example, a slightly different mindset is required for hand tool use as what may work with power tools, may not necessarily work with hand tools since other factors must be considered.

[Sean Hughto]

I once did a thread on another forum about making a frame and panel door. Derek was kind enough to preserve teh thread on his site. You can see how I make m&ts (at least for cabinet doors) there if you like:

http://www.inthewoodshop.com/Furnitu...el%20door.html