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Your Tenon Tightening Technologies

Tenons can simply be glued. We do it all the time and gluing them lasts just fine. Mostly we rely on clamps to seat shoulder lines and and keep the two parts married until the glue dries. When this has taken place it is unlikely you will ever be able to part the union without damaging one or the other or indeed both. It was and still is for some a marriage made in heaven!

Totally glue, animal glue, and nothing else. Two tenons in tandem and 150 years together and still totally united.

Before the advent of the screw thread and the now ubiquitous clamp that we derive our effortless clamping power from, craftsmen relied on the draw-bore method for seating joint lines and drawing up the tenons. On long rails that defy clamping we still use the draw-bore method for drawing up the tenon into the final union and indeed this method, as long as the shoulders were dead square, guaranteed that the outcome of frame making like sash windows, doors and window frames were indeed square. All too often we fail to realise that clamps misaligned to the long axis of the rails will clamp frames out of square because they will compress the stile fibres into a crushing submission. A well placed draw-bore hole and pin does not do this. Draw-boring mortise and tenon joints relies on two offset holes being bored separately in both the stile and the rail. The hole in the stile or leg, through the mortise hole and near to where the tenon shoulder meets the stile or mortise hole,  is first bored all the way through or at least part way into the second half if not bored all the way through. Then the tenon is pushed into the hole so that the tenon shoulder fully seats. To seat the joint full we use tapered metal pins called draw-bore pins. Driving or manipulating these into the hole when the joint is together pulls the two parts tightly together.  Placing the point of the auger bit back into the hole so that the snail point of the bit touches the tenon inside gives the exact centre of the position of the hole through the mortise. With the tenon withdrawn, we now bore a slightly offset hole nearer to the shoulder of the tenon but aligned centrally to the original hole. This distance will vary depending on the size of the stock. Timber frames for timber framed structures such as buildings may be offset 6mm and more whereas small wooden frames say for chair legs and rails need only be offset 1 or 2mm. The round peg, when driven, compresses at the intersection of the two holes, where they crossover, and the peg remains distortedly less in diameter on the exit side of the hole. Hence there is usually a gap on the exit hole side around the peg. This cutaway shows how the peg bends to conform to the offset and remains this shape for the lifetime of the joint. A sort of internal spring if you will.

Through-section showing the draw-bore pin through the tenon and mortise.

Wedging

Wedging generally relied on clamping for seating the shoulders. Why use wedges? In the early days of screw threads and iron clamps the clamps were expensive and few and far between. Not like today when most woodworkers own a dozen or so. Clamping followed by wedging meant the clamps could be used immediately on the next frames so as soon as the wedges were driven the clamps were removed to be used elsewhere.

The simplest of wedging was drive the wedges alongside the tenons. This was quick and effective but lazy. Here, the tenon is not cut to receive the wedges either side but the fibres of the tenon are compressed.

 

The next type of wedging was to simply drive wedges into saw kerfs cut into the tenon parallel to the long axis and allow the wedges to create pressure in the width of the joint, compressing the tenon width between the extremes of the mortise.

 

 

 

Another type is to slope the saw kerfs as cuts which send the tips of the wedges toward the inner reaches of the tenon. Opening up the outer aspect if the mortise creates a dovetailing effect. This is very strong and resists breaking off the outer aspect of the tenon which sometimes happens with the former method above.

And then there is the ever famed fox wedging of tenons in mortises as shown below.

Fox wedging is used inside non-through or stopped mortise and tenon joints. In this case the wedges must be precisely cut so that the kerf length in the tenon is slightly longer than the length of the wedge. That way the wedge is seated when pressure is applied via hammer blows or clamping pressure. Often the mortise ends are left square but, as can be seen in this joint, the opening out of the mortise facilitates the wedges and the tenon element of the joint becomes dovetailed and inextricable.

26 comments

  1. Dave W says:

    Amazing. I have never seen such excellent cutaway photos. The ever famed fox wedging is really cool. Thanks, Paul for posting this.

  2. Robb Smith says:

    I hadn’t heard or seen fox wedges before. I’ll bet those could leave someone scratching their head in the future when they are trying to disassemble it.

  3. Mic says:

    I don’t see a difference between the 2nd and 3rd photo of the wedged tenons. I would expect in the 2nd pic the wood to compress equally (if not more in the middle as there is more compressible material ) but it looks like the wedges look sloped and not parallel.

    Or?

    Mic

    • Hugo says:

      When I look closely I see the slope of the kerf on the 3rd, no? Showing that the efforts are transmitted inside the tenon.

    • Tim Brown says:

      I think the pictures are misplaced: in picture 3 the walls of the mortice are parallel, while in picture 2 they are angled. The pictures should be reversed.

  4. Peter says:

    Thanks for another interesting and informative posting on subjects which are basic, but improperly understood by many.

  5. Russell Lowe says:

    Brilliant pictures showing us the inner workings of the tried and tested jointing methods.

    I made some doors for two rabbit hitches last month,I used the drawbore technique for the first time,actually it was my first time ever cutting mortises.

    I had problems with the pins breaking out on the back side as they passed thru,I offset by 2mm,and made the pins the exact same size as the holes.

    I thought making the leading end of the pin smaller would fix it but it didn’t,anyway I came to the conclusion that I hadn’t made them completely straight,I used a door hinges to bash the pegs of wood thru to create the dowels.

    What do you think Paul,would having pins not straight cause them to blow the backs of the mortise peg hole out ????

  6. Rob says:

    Lovely stuff as always. I had difficulty when making my bookcase as I didn’t have long enough clamps, I thought about ratchet straps but it didn’t really work so I used the method Paul shows for jointing thin stock on a large scale. I used 4/2 studs cut away the section and drove wedges to bring the housings together. It worked great and I still use the now I hope someone might find this useful as not all of us have as many clamps as we might like. Thanks as always Paul and team

  7. Phill N LeBlanc says:

    makes me wonder how many methods and techniques of the past have been lost today. The ones we don’t see by dissecting old joinery. The tools that were made for a purpose that no longer exists. Tricks of the trade when the “trade” has disappeared.

  8. Rami says:

    Thank you very much for excellent photo and explanation.
    Can please elaborate on the metal draw-bore pins? what are they used for?

  9. Greg Marshall says:

    This post is so very instructive Paul! Thank you. The cut-away view of each style makes your explanations perfectly clear and these methods are very interesting. It would be very interesting to see a cutaway view of two mitred tenons coming together in a “corner” mortise like we saw recently in the Laptop Desk project as well.

    I really appreciate the lovely photography to go along with the words of wisdom you share with us. Thanks again!

  10. Gaëtan says:

    Let’s not forget the tusk tenon, a favourite of mine : it allows disassembly, reassembly, and tightening of the joint as needed. Plus I dig the rustic look.

    • Paul Sellers says:

      Draw-bore pins are tapered metal rods with handles on that slips through the holes bored for the final wooden pine that passes into and through the joint. By levering the tenon through the hole the tenon shoulder can be drawn into the hole. As the shoulder nears the stile the pin can be driven in and the joint shoulder seated. The pin is then tapped or pulled out and the wooden pine with along tapered point is driven through the joint as a permanent addition that both locks the tenon into the mortise and also stops the tenon from withdrawing.

      • rami says:

        I see, thanks for the clarification.
        In the blogpost it sounded like you use the draw-bore pins after you drill the hole in the mortise, but BEFORE you drill the tenon.
        All the best,
        Rami

      • Paul Bayliss says:

        Hi Paul,

        What would be the advantages of using the metal drawer bore pins versus simply clamping the joint and driving the wooden pins?

        Many thanks in advance,
        Paul

        • Paul Sellers says:

          Clamps with screw threads have not always been around. W have been born with the luxury of always having them and indeed, proven by your question, always taken it for granted that everyone has always had screw-threaded clamps just hanging around waiting to be used.
          Offsetting the the hole in the tenon meant the draw bore pins pulled the shoulder up to the stile and then replacing the steel pine with the inexpensive wooden draw pin pulled it finally home and kept it there.

  11. Tom Wheeler says:

    Have heard to use wet wood for the pin which will bend instead of compress and then dry in a locking dogleg.

  12. Andrew Cormack says:

    This answers so many questions I have wondered about! I’m not sure I fully understand everything yet, but I’ll analyze all this and work it out.
    Paul, a book on these old time skills would be really invaluable to the future of woodworking by hand.

  13. Igor says:

    Great insight in the inner workings of these joints!

    One other method is missing, also lesser known: butterfly-keys!

    Thanks Paul!

  14. Daniel says:

    Dear Paul,

    I’m building my first workbench as I write this comment and I was considering using wedges for the tenons. As you said, a well made mortice and tenon is a mighty joint but due to my inexperience I thought of wedges to force a tight fit with their pressure. Which method out of them all would you recommend me? Or should I discard the idea?

    Thanks for this post as I did not know of the “lazy method”, it may come in handy in the future. Actually, thanks for every single post, comment and video that you and your team produce.

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