Home » Paul Sellers’ Blog » When a Tenon Snaps

When a Tenon Snaps

Saturday 25th March 2017

So what do you do if a tenon snaps off when you least expect it? Such things happen, after all, and you have already invested good time in the buying and milling wood, forming tenons and even shaping the wood for its place in the whole. I have had it happen with dovetails too. It’s as if a tooth was pulled or something like that anyway. There is no doubt that such things can be very frustrating. The ultimate then becomes a question of integrity. Is adding a false tenon less than acceptable in the grand scheme of things. By doing such a thing does the joint have integrity and then of course your own integrity might be called into question too. After all, is this what your customer would or would not want? On the other hand, many if not most professional and amateur furniture makers and woodworkers actually rely on third-part components to unite the parts in place of a joint created in the solid wood itself. In whichever realm they choose they can be dowels, biscuits or dominoes, all of which are made from solid wood. But still, for the joiner and furniture maker, you know, the maker known for actually making real joints and not assembly parts for mass making, there has to be the question of personal integrity. The line for me is drawn here. If I am making a piece to sell I would replace the piece and eat the cost rather then sell something to a customer knowing that the piece is flawed by such a thing. My customers came to me knowing that I would make the project to the very best of my ability. There’s an expectation that goes with my work and and anything less is unacceptable.

Whereas repairing a missing tenon with an implanted one is absolutely acceptable in a piece in for repair for whatever reason and from whatever source, repairs in new work can indeed become questionable but not necessarily unacceptable. For example if something falls onto the edge of a new cabinet and damages the corner of an edge I would have no issue cutting out the flaw by ripping down the length of the top and adding on an additional half inch or more. This type of repair to new work is simple and often undetectable and most cabinet tops and tabletops are made up of several pieces by lamination as a matter of course anyway. On the other hand, depending where the damage occurs, a repair could render a piece unsafe. Ultimately the decision is yours. An apprentice once asked me if he could glue a long-grain break on a chair leg once and I told him emphatically, ‘No!’. “Why?” he asked, “isn’t the glues joint stronger than the wood?” “Perhaps.”, I answered. “But what if it is still breaks on or near the glue line? Then it could be argued that you knew of the weakness and glued it.” Any piece that you make that possibly becomes a safety issue should be replaced. In the case that follows no such concerns exists. Further more, however, I do not intend to sell the piece anyway, so it’s not an issue. In my case though, and it may well be a contributory factor in my decision making, the oak rail was a complimentary grain where the component was a perfect colour and grain match–it was indeed irreplaceable in the grand scheme of things. I decided I could indeed fit a false tenon to my rail. It certainly wasn’t a safety issue and neither was it a weakness. I have no intent to sell the piece either. By mortising the end of the rail 2 1/4″ in to create the pocket I wanted I soon had the new stem installed.

After boring out most of the waste I chiseled the hole to establish square corners.

It’s never easy to mortise end-grain with just a chisel because of the nature of the grain, so I bored out most of the waste first, which works well. I made the replacement tenon fatter than the mortise so that I could refit it to the mortise hole.

Two-ton epoxy works well for this type of work.

Once mortised, and with the tenon fitted to the rail, I then used two-part, two-ton epoxy to glue the tenon into its new hole. I do this rather than using PVA because I have no way of guaranteeing that no voids exist inside the hole.

I glued both the replacement tenon and the hole.

Putting a little excess glue in the hole and then applying force via clamping the tenon under pressure with clamps means the glue is forced up and into the walls of the mortise.

The glue squeezed under pressure forces the glue back up into any voids around the tenon.

With the tenon glued, and allowing the epoxy to fully cure, I am confident that the joint will hold.

So these are the ways we evaluate the integrity of our pieces. It’s not whether we will be ‘found out’ but whether we measure up to our customer’s expectation or indeed the standards we have set for ourselves. I know for me that I will always feel better if I have gone the extra mile.

14 comments

  1. B Power says:

    For me it has all to do with pride in your work. I would rather spend more time and money for the feeling that I’ve done my best and have no regrets at the end of the project. Pride in one’s work is something I see that’s missing from a lot of people now. It’s all about speed and savings and the almighty dollar.

  2. Matt Sims says:

    When you are making something commercially, i.e. it’s to be sold to a customer, there is, or should be a higher standard in place, and I agree wholeheartedly with what Paul has written here…

    However, when it a piece for “self” and such a mishap occurs, I suggest you can still do a “repair” and take pride…

    You should have the pride in the quality of the repair, or recovery, providing, of course, that the repair is of an adequate standard to merit such pride!

    Regards,

    Matt

  3. Randy Ewart says:

    Paul, the bottom line is that it becomes an issue of personal integrity. This is something that must be modeled, taught, and reminders given regularly in today’s culture. Sadly, it is missing in action far too often. Thanks for your example of personal integrity and sharing such a reminder to others here . . . .

  4. Blaz Grapar says:

    Doesn’t this say maybe that a joinery is too weak in the first place. It appears that a tenon could be much larger doesn’t it?

    • Alan Prescott says:

      Or an accident in the workshop, or just being a little over-enthusiastic disassembling a test assembly, or a hidden flaw in the timber or …
      The basic thirds rule of thumb in tenon sizing appears to be good here.

    • Paul Sellers says:

      No, that’s not really what it means at all. Sometimes, depending on a variety of influences and conditions, a wood can be more brittle in a particular area or section of a tree. Unfortunately it is not always evident. Out of a thousand or more tenons no such thing would happen and proportionally this tenon was indeed perfectly sized. There is something called the thirds rule but generally it only applies to thinner stock and usually it is used for door stile to rail ratios. Often it offers little real value but can be used as a loose guide.

  5. Jonathan Bass says:

    Integrity is doing the right thing when no one is watching. I try to live by this rule even when the project is for myself. I don’t want to look at a piece of work with a jaundiced eye knowing that I could have done better. Now in the above example, a floating tenon is an elegant fix. I apprenticed as a machinist, you remind me of my mentor with your ability to explain why you do what what you do rather than just saying “do it this way”.

  6. Mark Burns says:

    Interesting break
    If one were making this joint in iron or steel or bronze (tenoned joints were once quite common in wrot iron work – the ends of the tenon, in the absence of glue, were peened when hot into the flared open end of the mortice) one would, in order to avoid stress cracking under any load, radius the internal corners where the tenon emerges from the main section of the rail.
    I wonder whether a smoother transition, rather than the traditionally really sharp intersection, into the tenon would render it stronger. The flaring of the mortice to take it would be a matter of more precision, but would remain unseen.
    I suppose, as Paul comments, it’s more down to the peculiarities of the individual piece of timber, but nevertheless worth a thought IMHO

  7. Peter Littlejohn says:

    Some years ago a friend asked if I could repair (glue) their broken kitchen chair leg which had snapped because of short grain. I could see regardless of how good any repair to the original leg would be, it would just break again, so replacement was the only option.
    If whoever made the chair had taken a moment to look at the grain direction when setting out the pattern, this shorter grain could have been placed at the top on the chair back and not below the seat were it took all the weight. But that would have no doubt “mucked up ” marking out all the other legs on that board. “She’ll be right, just get the job done”.
    The replacement leg had long grain throughout and was a good colour match as well. My friend was amazed at how well I had “repaired” the broken leg and more so when I told them the whole leg was new. Taking into account safety and pride of workmanship is important on any repair, even a basic kitchen chair.

  8. Cory says:

    I have been a tradesman for nearly twenty years. It would be nice to say that when I do something wrong and make a mistake I simply “eat the cost”. It would be nicer to say that I never make a mistake. A long time a go I went to art school. I was taught then that a “real” artist is not the one who never makes a mistake, it is the one who can repair his mistakes and make them look natural.
    That said, if I make a mistake in my line of work it could potentially kill someone. So under the constraints of time and money, I make the best repair possible- which is to make it as near perfect as realistically possible. The repair is complete when I make it a mental imperative to not make the same mistake again.
    There are times when I must absorb the cost. But ask yourself how many times you can afford to absorb the cost of starting from scratch every time you make a mistake. Now compound that by all of the mistakes of those working for you. You would not last long in business.
    In the end, integrity is necessary, but it must exist within the context of the reality . It is fine for a hobbyist to say that they would simply do it over from scratch. Try doing it over for a living. This is what blows the myth of the craftsman purposely adding flaws to his work so it is not perfect.
    I think it is critical to face reality and consider what is practical concerning integrity for those of us who are considering woodworking as a career choice and not pontificate about integrity as if it were humanly possible to be perfect. I have made far too many mistakes in this life and been the object of far too much hypocritical head shaking from those who never applied their craft for a living, and I do far better work than most people care to. Thanks for this post Paul. It should give us all pause to think about our own practical integrity and what is ethically passable as corrections for our own mistakes. Simply said, we are always capable of doing what we do better. Aim for perfection. Now what do you do when you fail-which is always.

  9. Jack Kaup says:

    99% of the people who look at a project wouldn’t know if you used a biscuit or a
    tenon. I have been building things for 40+ years and some people would consider
    me a master craftsman, but it turns out I am just a machinist. Every mistake, accident,
    or fluke oddity must be judged on it’s own. Can you make it invisible? Will it be just as
    strong? Yes if you are making it for yourself it makes the decision easier. I have sold
    many projects and none have come back, but I don’t think I’ve ever made a “perfect”
    project. I can almost always see something in the fit or finish that could have been
    better. Thank you Paul for showing me that hand tools are still a great option. I was
    looking for a mortising machine when I saw your first video and have become a
    big fan.

  10. Daniel Hopwood says:

    Not having internet access at home makes me use public access once or twice each week. I copy the blog articles and save on a Mac with TextEdit, so I can read at home. The trouble is the photos come out HUGE! It takes a lot of time to reduce their size using Preview. Not having this trouble with other websites.

    I have all your books and DVDs published so far, and watch your YouTube videos. I want to thank you for imparting your knowledge so freely to all of us who are learning. You have a good manner of teaching.

    • Brian says:

      Hi Daniel,

      Is it possible to choose File -> Save Page As? On windows, if I do that I can just click on the .html file in the file system and the entire page comes out just as it was. Just a thought.

  11. jason says:

    A worthwhile discussion but IMO what you’re calling pride, I’m calling vanity.
    If your brand is more valuable to you than your time, you have every reason to split hairs over integral vs splines. If on the other hand, you have a reasonable amount of confidence in your brand and your work, then a spline isn’t a hack, it’s an upgrade that allows you to keep all the wood in the piece from the same board/filch.

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