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Thread: Help me understand windsor style tapered tenon joints

  1. #1
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    Help me understand windsor style tapered tenon joints

    I want to make a several benches with a heavy seat board and tapered tenon leg joints. Are these joints always wedged from the top? Won't the wedge work against the taper and eventually force the tenon backward? Why not just whack the leg farther in the taper to achieve a tighter fit?

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    If we are thinking of the same kind of joint, the mortise is bigger at the end with the wedge than at the end where the tenon is pushed in.

    On chairs and other items, I think this may be done with a spoon bit. A wedge is placed in the mortise and the tenon is then pushed on to the wedge. This causes the end of the tenon to fill the area and stay tight as long as the wood does not shrink.

    jim
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    Harlan, While I may not be the world class expert on this site I have built a number of Windsors. The leg tendon is supposed to fit the tapered hole exactly. The glue cements the leg to the seat and the wedge, properly installed, slits the tendon and forces all sides of the tendon against the side of the hole. That wedge needs to be set perpendicular to the grain of the leg so that the spit occurs properly and does its job. The weight of the person sitting on the seat drives the pressure into the seat/tendon joint. The type of bit used to make the hole in the seat is of little or no consequence as the sided of the hole are where the leg tendon rest and are held by the glue and pressure. - -hope this helps Phil
    Philip

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    An alternative

    OK, I've been working as an antique restorer and conservator for 30 years now (God - has it really been that long?) in that time, I've taken apart literally thousands of Windsor chairs of every vintage. The wedge joint, though initially effective and a relatively simple procedure, is in my opinion not the most effective method for a long-lasting joint. The earliest (and later best) chairs have always been made using the "bulbous tenon" joint, when the turning, preferably made out of still-green wood, is turned with a distinct, significant "bulge" in the middle of the tenon. The hole, drilled with a spoon bit, is not tapered, but simply by the act of drilling this way becomes larger in the middle if the hole depth than at the mouth or bottom. When the completed turnings are assembled, preferably with hide glue, the tenons must literally be malleted into their respective holes. Though a chair built this way will appear to flex a tiny bit more than a wedged joint at first, the hold is mechanical, and without a wedge held in tension only with adhesive. there is significantly less chance of longitudinal splitting, particularly of legs at the seat joint (where joint breakage most often occurs), and spontanious disassembly (like in the middle of Thanksgiving dinner - yes I have many stories like this) is reduced to a minimum. If fact, it's often very difficult to take apart chairs built with this method even after 200 years of use! I'm not disparaging the wedge joint, just pointing out that cutting a vee slot in the end of a tenon and intentionally putting a wedge in there can give you later trouble (BYITA) if the chairs are misused, as they often are when exposed to a houseful of teenagers.

    Just an alternative view. Hope this helps the discussion
    Last edited by Derby Matthews; 07-11-2010 at 1:44 PM.

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    Harlan,

    There are lots of great resources out there to give you some photos and further instruction, like Drew Langsner and Mikr Dunbar. Also check:

    http://www.windsorchairresources.com/

    In addition to the other comments above, the wedge is slighly wider than the top of the tapered tenon so it "keys" the leg into the seat to keep it from twisting. It's an amazingly strong joint when properly executed, especially if the undercarriage is placed slightly in tension (oversized to spread the force).

    Have fun, sounds like a great project!

    Kevin

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    Thanks for the replies. Now I have even more to think about.

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    Quote Originally Posted by Derby Matthews View Post
    The earliest (and later best) chairs have always been made using the "bulbous tenon" joint, when the turning, preferably made out of still-green wood, is turned with a distinct, significant "bulge" in the middle of the tenon. The hole, drilled with a spoon bit, is not tapered, but simply by the act of drilling this way becomes larger in the middle if the hole depth than at the mouth or bottom. When the completed turnings are assembled, preferably with hide glue, the tenons must literally be malleted into their respective holes. Though a chair built this way will appear to flex a tiny bit more than a wedged joint at first, the hold is mechanical, and without a wedge held in tension only with adhesive.
    Derby:

    Fascinating detail. Help me understand something. You say the leg is turned while green. Is it allowed to dry/cure before assembly, and if so, doesn't shrinkage cause the joint to get sloppy?

    Thanks.

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    Quote Originally Posted by Stanley Covington View Post
    Derby:

    Fascinating detail. Help me understand something. You say the leg is turned while green. Is it allowed to dry/cure before assembly, and if so, doesn't shrinkage cause the joint to get sloppy?

    Thanks.
    Yup. I think the previous poster misspoke or got tangled up in his underwear. Most legs are turned green but must be allowed to dry. The tenon can be dried to such an extent that is will swell in the mortise when the surrounding mortise wood equallizes in moisture content. This usually is applied to the leg stretchers.

    The method of putting a wedge in the bottom split then driven into the hole thus wedging the tenon tight is called a fox wedge.

    A well match tapered tenon and mortise can barely be pulled apart without twisting when it is tapped to together. For more info, you can also check Peter Galbert's "Chairnotes" blog.
    Life's too short to use old sandpaper.

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    I wear clean pants every day and don't bother with underwear. I may have misspoken though. I used the term green to mean cut, riven and stack dried, not kiln dried wood. Sorry if that threw anyone off. When you assemble bulbous joints that are prepared correctly they are pretty difficult to knock together, and I assume whatever shrinkage the rung undergoes afterward is matched by similar shrinkage in the leg or seat hole, I dunno.

    What I do know is that joints made this way are exceedingly difficult to get apart even if they have little or no viable glue in them. I've resorted to glue injection many times with chairs made this way, and am consistently impressed with the strength and rigidity of these joints.

    I've also made a lot of money over the years repairing wedge joints that have failed catastrophically right at the point of the vee cut for whatever reason, so I personally would not choose to build chairs using that method.

    Again, not disparaging them, and I bet there's a wedgie camp out there just as supportive of using them as I am not. I've only seen the hundreds of legs that broke come in to my shop, not all the ones that didn't.

    I'm just sayin....

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    Quote Originally Posted by Derby Matthews View Post
    What I do know is that joints made this way are exceedingly difficult to get apart even if they have little or no viable glue in them. I've resorted to glue injection many times with chairs made this way, and am consistently impressed with the strength and rigidity of these joints.

    I've also made a lot of money over the years repairing wedge joints that have failed catastrophically right at the point of the vee cut for whatever reason, so I personally would not choose to build chairs using that method.
    Derby:

    Thank you for the clarification. Are you aware of any books or articles that describe the details and proper execution of this joint?

    I am always fascinated by comments from people that have extensive experience fixing failed furniture, because their perspective goes beyond theory, custom, tradition, and personal preference. If a method or detail works well enough to survive a hundred years or more, then it is a good method/detail, and one I want to use in my work. If a high percentage of furniture using a particular method/detail fails over time, then I want to avoid that method/detail, regardless of the theory currently in vogue, the traditions I may hold dear, or the (often self-serving) opinions of tool/widget salesmen and scribblers.

    Please continue to share your insight. Better yet, write a book. Here's a recommended title: Failure Analysis of Historical Wooden Furniture; What Lasts, What Doesn't, and Why. I will buy the first ten copies, and use nine as Christmas presents to friends and libraries.

    Stan

  11. #11
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    I like Dunbar's Book "Windsor Chair Making: It is concise and well illustrated. Off all the many woodworking books I've bought and then let go over the years, this one stays in the library.

  12. #12
    Quote Originally Posted by Stanley Covington View Post
    Derby:

    Fascinating detail. Help me understand something. You say the leg is turned while green. Is it allowed to dry/cure before assembly, and if so, doesn't shrinkage cause the joint to get sloppy?

    Thanks.
    The tenons themselves are dried in a coffee can full of hot sand and then inserted into mortises drilled in green wood. Tenons swell, joint is locked. Hot hide glue helps swell the tenon.

    All chairs need some ongoing maintenance. There never has been, nor will there ever be, a way to make a chair that will last for over a hundred years of actual use and not get a loose joint from time to time.

    You can stick one in a temp and humidity controlled museum and not allow anybody to ever sit on it and the joints MIGHT stay tight.
    Last edited by Steve Dallas; 07-14-2010 at 7:19 AM.

  13. #13
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    Quote Originally Posted by Steve Dallas View Post

    All chairs need some ongoing maintenance. There never has been, nor will there ever be, a way to make a chair that will last for over a hundred years of actual use and not get a loose joint from time to time.
    I have a friend with a rocking chair made of some type of green, bent saplings, about the size of a finger. It was the property of his grandfather, who died before he was born, and has been in use for over 100 years, in houses with children (he has five of his own). Most of the joints are simply flattened on one side and NAILED. The seat and back slats are bent properly so it is as comfortable as any chair I have ever sat in. I didn't see any glue used at all. It is still quite tight and my guess is it will last the next 100 years. It looks to me like the wood was green when the chair was made and the drying process only made the nail joints tighter.

  14. #14
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    Tapered Tenons

    Quote Originally Posted by Derby Matthews View Post
    OK, The earliest (and later best) chairs have always been made using the "bulbous tenon" joint, when the turning, preferably made out of still-green wood, is turned with a distinct, significant "bulge" in the middle of the tenon.
    Hi Derby.

    This is an interesting idea, but I don't really get how it helps the joint and believe it probably weakens it. I have built a number of windsors, but would not claim to be an expert. As I have learned, the key to the joint is execution of the taper on both the mortise and the tenon. I was taught to turn the taper using one of a variety of jigging methods and then use a homemade reamer to taper the seat to the same taper. John (Jenny) Alexander's Green woodworking web site has plans for the reamer. I have never used spoon bits.

    The problem I see with the "bulb" is that you are effectively reducing the contact area of the joint, which is what gives it its strength. The mortise below the "bulb" starts off smaller than the bulb. Then you drive the bulb into the mortise and expand the lower section because the bulb has to force its way in. I am sure the wood gives some and then bounces back, which is why years later you have a hard time taking the leg out. But the end result is that the portion of the tenon below the bulb is looser than the top. I don't think this is good.

    I also like the fact that with a well executed straight taper, the joint tightens itself up with use. I have a chair that the legs are coming thru the top (need to fix), because of shrinkage, but the chair is rock solid. I think the bulb will act to stop the tightening because the taper of the bulb is different than the rest of the mortise. With pine as a seat material, it probably will give enough to allow the joint to tighten up, but I would worry about splitting the seat, even in the assembly process originally.

    Its an interesting discussion in any event.

    Regards, Patrick


  15. #15
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    Quote Originally Posted by Derby Matthews View Post
    I wear clean pants every day and don't bother with underwear. I may have misspoken though. I used the term green to mean cut, riven and stack dried, not kiln dried wood. Sorry if that threw anyone off. When you assemble bulbous joints that are prepared correctly they are pretty difficult to knock together, and I assume whatever shrinkage the rung undergoes afterward is matched by similar shrinkage in the leg or seat hole, I dunno.

    What I do know is that joints made this way are exceedingly difficult to get apart even if they have little or no viable glue in them. I've resorted to glue injection many times with chairs made this way, and am consistently impressed with the strength and rigidity of these joints.

    I've also made a lot of money over the years repairing wedge joints that have failed catastrophically right at the point of the vee cut for whatever reason, so I personally would not choose to build chairs using that method.

    Again, not disparaging them, and I bet there's a wedgie camp out there just as supportive of using them as I am not. I've only seen the hundreds of legs that broke come in to my shop, not all the ones that didn't.

    I'm just sayin....
    Good to know we're on the same page Derby. Maybe I misread! Thanks for the clarification.

    Bob
    Life's too short to use old sandpaper.

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