First, Add No BS


One of the turning points in my writing was courtesy of Bob Flexner. Years ago we were discussing ideas for future columns that he could write, and Bob threw out this one: You don’t have to finish both sides of board.

I laughed because I thought he was joking. Everyone else, and I do mean everyone, had told me you had to finish both surfaces of a board to prevent it from warping. Bob dissected the myth, eviscerated it. Here’s a later column Bob wrote on the topic for Woodshop News.

Bob’s column was fantastic. And it changed my thinking process immediately. Whenever I evaluate or explain a technique, I ask myself: How do I know this? Am I certain that every word can be demonstrated? Am I just repeating something I’ve read elsewhere?

It’s the same strategy I used as a crime reporter for newspapers. Every sentence of my articles went through those filters because if I slipped up I would end up sued. But I hadn’t applied that to woodworking writing. After all, this stuff had all been figured out thousands of years ago.

It’s an easy trap to fall into. And I’ve been climbing out ever since.


This week I’m cutting up a bunch of joints to see what is happening inside. When I first learned this staked furniture joint, I was told that you should use a hard wood for the legs and a softer wood for the seat, and that you should hammer the legs home hard. Like John Brown above.

It makes sense, but why? My theory is that the joint works much like a cut nail. The leg or nail crushes the fibers in the seat, helping to lock it in place. But is it true?

— Christopher Schwarz

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40 Responses to First, Add No BS

  1. Sean Hughto says:

    FWIW , my empirical experience in this realm is that wedges split wood fairly readily (a tapered tenon is a nice round wedge after all) and that both top locking wedges and tapered legs pounded home aggressively will often result in splits (yes, even when you orient the grain correctly). An untapered mortise and shouldered tenon with a locking wedge driven from the top only until the tone of the blow signals the wedge is home is the most fool-proof. YMMV. I’ll be curious as to whether you conclude that tapering is somehow necessary to achieve some significant benefit.

  2. diondubbeld says:

    Would grain direction on the leg “nail” make a difference?

  3. I thought the more important thing is that the legs are very dry so the tenons don’t shrink? But then again, I know nothing – seriously.

    I’m reminded of a great quote that a very generous woodworker here in North Carolina has hanging in his shop.

    “I’ll gladly tell you how I do something. Just please don’t confuse that with the right way to do it, and almost certainly not the only way.”

    • Daniel Roy says:

      Believe me, I don’t know anything but, a Winsor chair maker told me that a tennon on a spindle/stake (whatever it’s called on a chair) will go out of round as the wood shrinks and that the hole in the seat goes out of round as it shrinks (like Chris’s post about the holes in his Roubo bench going out of round). He stakes them together so that, when the wood swells and shrinks with the humidity, etc. that the out of roundness is 90 degrees to each other. He says he does not have to wedge the tennon.

  4. Vic Tesolin says:

    Great blog Chris! I’ve also started thinking about the skills and techniques that I use and where I got the information. There is nothing worse than being asked why you do something and answering ‘because that’s how I do it’. Asking yourself why is a good thing.

    • Daniel Roy says:

      I disagree there is nothing worse. Chris often answers ‘because that’s how I do it, it works for me’ and he qualifies this with it’s not the only way.
      Indeed, asking why can be a very good thing.

  5. luce32 says:

    Well, is it true?

    • I still have a couple more test joints to make before I conclude anything. I have to see how much fiber compression/deformation there is in an all-oak joint.

      In pine and poplar mortises there is significant deflection that is directly related to how hard you seat the tenon at assembly. But that alone doesn’t tell me what I want to know.

  6. Ben Lowery says:

    John Brown: Wearer of Jaunty Caps.

  7. carpenterman says:

    What a universal truth!

    ‘I ask myself: How do I know this? Am I certain that every word can be demonstrated? Am I just repeating something I’ve read elsewhere?

    That is one of the most profound statements I have red/heard in a long time, perhaps ever.
    Thank you for that.

  8. I had never thought TO finish both sides, but then my first exposure to quality woodworking was in a violin shop and those things are splendidly bare on the inside. Plenty develop a crack over the course of a couple hundred years, but for such thin, stresses, manhandled wood, I don’t think a little more finish would solve that…

  9. raney says:

    in both your test joints, looks like you’re checking the poplar engrain for compression — I’d think you’d see the compression more on the long grain. So wouldn’t you want to dissect in the other plane?

  10. Rachael Boyd says:

    on the finishing of both sides of the wood. I have never finisned both sides exaept when both sides are exposed to view. have never had a problem.
    on the round taper leg holes. I had some wood I got to make a hall bench it was 2×12 had nice grain but very white ,got it at a big box store. well it was the worest wood I have ever tried to work, no matter what I did it would tare out even with a scarper. so I ended up using it for milk stools ( I make them look really old anyway) and as soft as it was it never split when driving in the legs and there was no way they would ever come out. so there is something going on in there with the fibers locking with each other.

    • Rachael Boyd says:

      I am thinking its more like driving a piling into the sand a some point the friction is so great that even though its sand it will not move any more up or down and the same thing with the wood its not the force on the sides of the hole its more the friction.

  11. richmondp says:

    Great blog. Skepticism toward received wisdom is always healthy, in my opinion, and I look forward to any objective evidence you can develop, on any aspect of woodworking. I wish that Bob Flexner, in the article you cite, offered more empirical evidence for his assertion that wood need not be finished on all sides to prevent warping. He may well be right, but he offers little experimental evidence in support of his theory (compelling though it be), and thus is not entirely convincing, at least to me.

    • Bob can talk your ear off about the vapor- and oxygen-permeability of film finishes (he did that to me). So if you do a little digging I think you might come to the same conclusion.

      About a week after I had that conversation with Bob, I was discussing it with Don Williams, who is now retired from the Smithsonian. He said, and I think this quote is almost 100 percent correct: “I have seen maybe 10,000 pieces of old furniture in my career. And when I see an old one that was finished completely inside and out, that will be the first.”

      Give it some thought and dig a little yourself if you like.

      All best,

      • cmhawkins says:

        Bob Flexner is as expected correct. “Film Properties of Plastics and Elastomers” by Laurence W. McKeen” is THE authoritative reference for this subject. The author compiled hundreds (maybe thousands) of permeability measurements for all commercially significant plastics and elastomers in the scientific literature to create this book. The summary is that no commercially significant organic material at a thicknesses of less than 0.010″ can retard water vapor or oxygen transmission to the level which would prevent moisture content in wood from changing significantly during seasonal variations of temperature and humidity.

      • richmondp says:

        Nope, no digging for me, although it’s a noble idea; I’m far too lazy. I’ll wait for my favorite magazines and blogs to do that for me. In the meantime, I am trying to develop some perversion of Occam’s Razor, something to the effect that, in the absence of a compelling reason to buy more tools, use more complicated joinery, finish more surfaces, etc., always pick the method that requires the fewest tools, the simplest joinery, and the least finishing. (See comment above on “lazy”) In the present case, not knowing one way or the other, that means that I never finish the inside of furniture. Never have. I hate finishing. On the other hand, I always finish both sides of a new exterior door, not necessarily because I believe it necessary, but because the manufacturer’s warranty is void if I don’t.

  12. spokeshave27 says:

    It’s easy to get caught up in the paralysis of analysis, wasted a lot of time and good wood.

    I await your findings with interest.

  13. joeyb5 says:

    This sort of thing is precisely what you do best — bravo!

  14. Daniel Roy says:

    I just can’t believe he hasn’t been sued yet!

  15. Brian says:

    Do you really think JB was smacking those legs as hard as the photo makes it look? A few details make me wonder:
    (i) he’s not a very big guy
    (ii) i can’t see the mallet head, but the handle doesn’t look very robust. (watched a video of Frank Klausz last weekend and noticed that he seems to always choke up his heavier mallets)
    (iii) old photographs like this were produced on low-speed film. So the photographer would have asked him to pose. One/both of them might have thought the big swing looked better. But even if that wasn’t the case, its more comfortable for most people to take an object past parallel when they’re asked to pose. (don’t believe me? pick up a baseball bat and see if you like posing with the tip pointed straight to the sky, or if you find yourself doing more of a barry bonds impression)

    Although I’d love to think I’m noticing something new about the photo, I’m probably just jaded by all the times where hitting something harder has yielded sloppy results. (Most recently, in my experimentation with 5/8″ dia * 10″L oak drawbore pins. I guess your passion for drawboring got to me so I enthusiastically concluded: bigger and harder would be even better!… my mistake!)

    • It’s not just the photo. Many chairmakers (including Dave Fleming, who first taught me) drive the legs home with surprising gusto. Especially for someone from a joinery background, who is used to joints going together without fuss.

      • Brian says:

        Interesting. Funny that chairs and workbenches share a set of essential requirements (longevity, load bearing, stability) and yet their joints are put together so differently. Other than the habit we have of sliding chairs along multiple axes, why this dramatic difference?

    • Sean Hughto says:

      In the book, IIRC, Brown say he uses elm for its interlocked grain to minimize splitting, but adds that he has nevertheless split seats with this operation.

      • Yep, I think the use of elm is a major factor. You can hit the legs much harder, but there is still a limit. I have no problem believing that John Brown was hitting them as hard as it looks in the photo.

  16. woodgods says:

    Kind of like a morse taper effect but in wood.

  17. Kevin Adams says:

    Thanks for the pic, Chris, I do miss that Anarchrist Woodworker. And thanks for keeping his spirit alive, I saw that in you many years ago. Bang those legs home!

  18. Jennie here
    Seventeenth Century furniture stock is usually not even planed on the interior side, let alone finished. The inside looks like a cat relieved itself in a knitting basket. All layout is and has to be scribed with a scratch awl on the outside of the piece. In a way the joinery is skin deep. Check out the pictures in Make a Joint Stool from a Tree, The drawbored mortise and tenon was the principal means of joinery. It is rather down and dirty but it works. It follows that the dovetail is not a usual joint in the period. It is just about impossible to dovetail two pieces of uneven and irregular thickness. But you can mortis and tenon provided of course that only the very outer edge of the outside tenon shoulder touches the mortised stock. I could not believe it, but it is so. Don’t believe me ask Follansbee.

  19. Kinderhook88 says:

    We have to be like scientists, willing to change our mind about what we think it true. I remember reading about a torture test on dovetail joints. The conclusion was that the angle didn’t matter as much as we thought. (sry, I don’t have a source here…)

  20. error4 says:

    does the same go for water-based finishes? He says it doesn’t go the same for veneers with water based glues. There you have to do both sides. I would think that milk paint and latex have at least as much water as water based glue…

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