Clinching Nails (Sometimes Teeth)

I’ve been clinching a lot of nails these last few weeks while building some utilitarian boxes. So I’ve been digging into the literature to investigate the best way to do it.

Clinching (sometimes spelled “clenching”) is when you drive a nail that passes through both thicknesses of wood you are fastening. The tip of this nail sticks out about 1/4” and is bent over and driven into the wood.

Clinching adds remarkable strength to a joint. A 1948 study by the U.S. Forest Products Laboratory concluded that clinching can increase the holding power of a nail between 45 percent and 464 percent – depending on a variety of factors, including the species of wood and its moisture content. (For the complete super-geeky report, click here.)

Also interesting: The study concluded that bending the tip across the grain increased the holding power by 20 percent compared to a nail clinched along the grain.

But how do you best clinch a nail? There is more than one effective method.

Four Ways & A Trick
Here’s how the machines do it: They fire a nail in at an angle and there’s a steel plate waiting for the tip when it emerges. When the nail hits the steel it bends over into the wood – essentially it ricochets like a bullet or pool ball.

I’ve never tried this with a pneumatic nail gun, but it sounds like fun on a Friday afternoon.

For the hand clinchers, there are at least two common techniques. The first one is to drive the nail through the work. Rest a steel plate, anvil or a second heavy hammerhead on the nail’s head. Then tap the tip of the nail with your hammer. It will curl over. Then you can drive the drooping tip back into the wood.

The second technique is similar to the machine process. You drive the nail through the work and against a waiting “bucking iron,” which curls the tip and forces it back into the wood. (For a nice illustration of these two methods, click here.)There’s one more technique I’ll sometimes use when I’m being really, ahem, retentive. I’ll drive the nail through. Then I’ll use needlenose pliers to bend the tip to the angle I want. Then I’ll drive it into the work. This results in a tidy appearance. I admit it’s a bit much.

When I have a lot of clinching to do, I’ve found that a cast iron table saw wing can be your best friend with flat work – doors, lids and the like. Lay the cast wing on your bench and then you have a nice big area to support your work as you merrily clinch away. And no, the clinching does not mar, crack or otherwise defile the wing.

There is one disadvantage to clinching. It can alarm your children. After I finished a lid I showed the 30 or so clinched nails to my youngest.

“Ewww,” Katy said. “Dad, does this wood have termites?”

— Christopher Schwarz

About Chris Schwarz

Publisher of woodworking books and DVDs specializing in hand tool techniques.
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17 Responses to Clinching Nails (Sometimes Teeth)

  1. Terry says:

    Chris,
    When I was a kid, some(ahem)years ago, my Dad was always clinching nails for some repair or building project,usually at the farm he grew up on and which my Grandmother still lived. The extra holding power was needed for gates, fence boards, board doors etc. We always had a few flat irons (cast iron clothes irons minus the handles) kicking around that worked great for clinching and a host of other uses. I was the official "iron man" that held the flat iron up against the board the nail was being driven through. As Dad hit the nail the flat iron would bounce my hand (and sting like crazy if I held it too loosely)and as the nail came through it would curl over like magic. It worked like a mini hammer mill. Living in that same house now, I still occasionally find boards that bring back those memories as I rediscover them.
    Long before my Grandparents (and Great Grandparents) lived in this house the builder installed two cellar doors, an outer and an inner. Both of those board doors are clinched nailed and have not been repaired in 120 years. The only way clinch nailing fails is if the nails completely rust away. And have you ever tried pulling one out that you didn’t know was clinch nailed??
    By the way, those cellar doors have a very interesting joinery feature that I have yet to see elsewhere. The vertical boards are clinched nailed together on the backside with the normal 3 "Z" boards. The diagonal board is actually jointed into both horizontal boards to eliminate any chance of the door ever sagging. Pretty neat and definitely old school. Will send you a picture if you please.

  2. rfrancis says:

    Do you have problems with store bought cut nails being too hard (brittle) for clenching. I find that they break off. Do you temper them first? Or do you buy the designer nails?
    And have you seen the clenching iron on the Wooden Boat Store website? You definitely need one(or two) to go with all those hammers.

  3. farms100 says:

    several times over the years while using an air finish nailer on trim. I have had the nail hit something metal under the the board and curl around and come back through the work piece. One time it blew out a chuck of weak grain and hit me in the arm.

  4. Christopher Schwarz says:

    You can use wire nails. If you read the government study they are using brights and cement-coated nails (the difference between the two is interesting). As you found, some nails are more brittle than others.

    I use mostly cut nails in my work, which are easy to clench. Here’s my secret: Buy them off eBay. They’re as cheap as wire nails. I just bought four full 1 lb. boxes for $6 – the shipping was more than the nails.

    Chris

  5. Kolin says:

    Chris
    I am a 31 year old woodworking student, intrigued by the idea of hand tools, and how they may have been used before power tools were readily available. I have attended modern carpentry classes on a college level for some time now, and I am building my own small library of books. I recently discovered your blog, and was hoping you might recommend some literature on carving techniques. Also, I am interested in wooden ship building, but cant seem to find anything on the shipwright trade. Is this trade still around, or is it now extinct? Replica ships were made for recent Pirate movies. I wonder how the prop man knew what to build. I am starved for resources on these subjects. Any input would be a great help. Thanks

    P.S. Old Cut Nails always shear off for me too. Thank God for modern metals.

  6. Christopher Schwarz says:

    Kolin,

    There are tons of resources out there on both topics. On carving: Chris Pye. His books. His DVDs. His classes.

    On traditional boat building: Get a copy of Wooden Boat magazine. Goto their online bookstore. You’ll be swamped with good information.

    Good luck!

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  8. Mark Clench says:

    They say that surnames were first given acording to the occupation you held. Maybe that means my ancestors did a lot of "Clench" nailing. Guess I’ll have to practice this technique so I can revive the family business.;)

  9. Good article.

    Just a week or so I was clenching some nails for a garden trellis (no, it wasn’t pretty, but it is still standing). On a particularly tricky joint, I ended up hitting the wrong nail – mine. Oddly, enough it was a nostalgic moment and made me reflect back on the lives of my Dad and Grandfather.

    Luke

  10. Gary Roberts says:

    Not quite woodworking… years ago I worked in a leather shop. No, Chris, not That kind of leather shop, just a plain old shop making sandals, belts and bags. We used copper tacks, hammered against a steel plate to clinch them. I’ve continued to use this method when clinching wire nails.

    Gary

  11. Jan Goris says:

    One of our lines of business is building crates, hence we utilize type one clinching. Our table is 4′ by 16′ and is covered with a 1/4" steel plate. Clinching creates a strong joint but just as important, if you want to bring home the bacon, clinching is very fast. Yes, it is kind of fun for a Friday afternoon, but on a Monday thru Friday basis I’m glad it’s the young guys wielding the pneumatic hammer.

    Jan

  12. Ross Graham says:

    Thanks Chris

    I grew up on a small farm and use to follow my father around as an "apprentice/helper/indentured servant", he often would clinch his nails especially when he built gates – I always figured that he had measured the width of the boards wrong and just bend the nails over – certainly wasn’t going to explore it! Now I know the rest of the story, I think :-)

    Ross

  13. Ethan says:

    Chris,

    I can personally attest to the strength of clinched nails. My supply of reclaimed white oak all comes from an old house my brother and I dismantled on the family farm. The entire house was sheathed with 10′ long vertical white oak boards (in pristine condition as they were covered with cypress clapboard siding), nailed into at least three horizontal framing boards, with an average of six nails per intersection. Every single nail was clinched.

    I can’t even begin to tell you how long and arduous a task it was to remove the boards from the frame in one piece and then remove the nails from the boards!

    Oh, and while the shingles were all put on with square cut nails, the sheathing was attached with wire nails.

    Ethan

    BTW… I noticed you were able to squeak in a photo of you with one of your hammers. I sense an ulterior motive to this blog entry…

  14. Glen says:

    Thanks, all.

    I’m with Ross. Every I’ve come across a board with clinching I seriously thought the builder was too poor or too lazy to buy the right length nails.

    Thanks for the lesson. Good article.

  15. Mark Clench says:

    I think there is a difference between "clinching" and bending over a nail that is too long. For example, in framing a house made of 2×4 you often see carpenters bend over a nail and pound it beneath the surface of the wood, that is not considered clinching is it?

  16. Rod says:

    If I’m using a claw hammer to nail, I clinch the nail by using the claw to bend over the tip of the nail (instead of pliers) then hammering it over. No need to carry an extra tool, and the hammer has better leverage.

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