Medieval Method Can Improve a Modern Design - Popular Woodworking Magazine

Medieval Method Can Improve a Modern Design

 In Chris Schwarz Blog, Woodworking Blogs

I recently finished building an Enzo Mari table from the 1970s as part of an article for Popular Woodworking Magazine, and I have only one worry about the project.

It looks great. It feels stout. But I’m worried that the joinery might not last forever.

The joinery? Lots of properly installed wood screws, with diagonal bracing to reduce or eliminate racking. But screws can come loose and might allow the table’s base to rack.

While you could build the table with mortise-and-tenon joints, that wasn’t the intent of Mari the designer. The table is supposed to be easy enough for a beginner to make with simple tools.

Clench nails ready to be driven against the steel plate. Note the angle of the nails.

After some thought, I think that “clenched nails” might be the answer.

Clenched nails hold together some of the oldest pieces of woodworking extant today, including doors that still function quite well. The trick to using the nail is it is driven through the two boards you want to join and its tip is bent or turned over like a fish hook back into the backside of the lower board.

Turn the joint over and you can see the tips of the nails bent over back into the board.

Clenching locks the two pieces together and the joint can last 1,000 years or so.

When I clench nails, I drive the nail through the boards at an angle with a steel plate below the boards. The angle helps the nail’s tip bounce off the steel and turn back into the wood. The angle also allows the tip of the nail to clench across the grain of the lower board, strengthening the joint even further.

Three wire nails bent like this when I tried to clench them. The sunk nail is a clench nail.

A Bright Idea?
I’ve clenched a lot of nails in my life, but I’ve always used special “clench nails” from Tremont that bend easily and properly. I decided to see if standard bright wire nails from the home center would clench.

Long story short: I didn’t have any success. After varying the angle several times I found that the wire nails simply bent under the head every time. Clench nails have a thickened shank that prevents them from crumpling.

Try it for yourself, but I’m going to go back to my clench nails for this operation.

After much abuse, the wood failed before the nails would pull loose.

After assembling a few sample joints from the Mari table I tried to pull them apart. The wood failed before the fasteners came loose.

That’s a good joint.

— Christopher Schwarz

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Showing 7 comments
  • maxbroome

    As others have said, you have to clench wire nails individually from the point side. I have been pretty successful with about 1/4″ or a little more extended beyond the face of the wood and using my nail set to start the tip moving horizontally. If I am not concerned about appearance, I will then just wale away with a hammer and clench them over leaving hammer dimples around the nail. If concerned, you might try clenching completely with the nail set or a small flat punch. As mentioned before, not sure why you would be concerned given that clenched nails look pretty bad to start with. I generally use this method when building a laminated beam as a joist support. I’ve never had a clenched beam separate even in outdoor exposure like a deck or patio.

  • orbsphere

    The bent wire nails as shown seem to be longer than the clench nails by about the thickness of one of the boards. Use wire nails similar in length to the clench nails or . . . practice driving wire nails more LOL (I am making a joke about needing practice). If wire nails of similar length were used we should only see about 1/4″ max. proud of the nail head end above the surface. Try driving the wire nails all the way through then flip joint over resting heads on metal plate and then clench nail ends. The fragmented wood is ugly when clenched as noted in article when driven through to metal plate. Aren’t better results found when clenching the clench nail points while head end is resting on the metal plate?

  • EastLine

    I was at an auction last week and spent a few minutes distracted by a large barn door held together with clenched wire nails. I’m glad this article was posted now, because it reminded me of that door and I’ll have to remember this technique the next time I built something where durability is more important than style (unless I can hide my crimes).

  • gtrboy77

    The only problem with clenched nails is that they look absolutely tacky as all hell. Other than that, they are functional.

  • MCamaleri37

    I have had success clenching the Rivierre square-shank nails as well, for what it’s worth.

  • Lukeallister

    I’ve had good results clenching wire nails by adding a pair of needlenose pliers to the process.

    Instead of putting the metal plate under the tips and driving the nail at an angle, I drive them all the way through, flip the piece, and put the plate under the heads. Then I grab the nail shank with the needlenose pliers and hammer the tips over. The pliers help to bend over just the tip instead of bending the nail at the wood junction.

    Then I hammer the nail down across the grain. The results are strong (and much more attractive than my earlier attempts). This method enables you to use the $3/box nails from the home center–certainly in the spirit of Enzo Mari.

    Some pictures here:

  • bob_easton

    Brilliant substitute!

    Clenched nails have been holding hull planks on (smallish) boats for centuries. It is common to use copper nails for boatbuilding, first to endure water (esp salt water) and second because they are easily clenched, unlike those high-tensile wire nails.

    P.S. some small boat builders also use the spelling “clinch” nailed.

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