Pinning Tenons

I don’t know how many pins I’ve put in chair slats, but I’m sure it is in the thousands.

My process evolved over the decades, eventually settling on the one I show in this video below.

Early on, I had all sorts of problems getting perfectly consistent pins and having them look fairly uniform. I initially thought using hickory for all the pins strengthened the joint. What actually happened was that in order to get a square hickory pin to fill a round hole.

I risked splitting the legs of softer woods like cherry or walnut.  So, I settled on using the same wood for pins as the chairs were made of.  It seemed that the softer pins gave a little, and I nearly eliminated the risk of splitting the legs.  I split the stock for pins, then dressed the split blanks and sawed the pins out on the bandsaw. I cut them exactly the same thickness as the bit I used to drill the hole.  This helped production and split risk because of the consistency in dimension.

Before that, I would split each pin from super dry stock to ensure strength and shave them to thickness with a chisel resting on the drill I used. That worked fairly well, but sawing riven stock is the way to go. I generally make a few hundred pins at a time and keep them in the kiln so they hold their dimension.

You’ll notice in this video that all the pins are cut to length so that I don’t have to cut them once I drive them in.  This made the process faster, and drilling the holes to the exact depth of the pin length made pin breakage a rare occurrence. This prevents breakage because the pin never bottoms out.   I drill the holes to the exact length of the pins (usually .750”), then I leave the heads proud of the surface by about .030”.  That’s enough to carve a nice pyramid to finish off the pins. Leaving that little space at the bottom of the pinhole minimizes pin breakage and blow-out on the back of the leg and the potential that a shrinking leg pushes the pin out a bit.

I use a Japanese hammer with a slightly domed face.  I like the balance of this hammer and the doming of the face helps prevent splitting the pins as it makes it easier to stay off the corners with each gentle blow. 

Shaving the pins in a group of 6 helped keep the chisel level and all pins uniform. I used to chamfer each corner with a knife, which took long enough to allow me to devise a quicker way.

You’ll see me tap each pin into a hole in an aluminum plate.  I just used a 90-degree bit 3/8” diameter and made a cone-shaped hole large enough to make an easy target and shallow enough to keep my fingers safe from hammer blows. One tap gives me four perfectly chamfered entry corners. I was surprised at how much difference this made.  The pins start more easily and drive straighter due to the perfect chamfers.

Before this level of consistency in dimension and shape, I would find that the pins would sometimes rotate as I drove them.  I would hold them with an adjustable wrench to try to prevent this, and it helped.  But now and then, I would get a little stinker that would suddenly twist just to piss me off.  So, I came up with one more trick. I took an old auger pit and cut its shank off.  Making sure it was the right size, I tried tapping its squared end into a hole to see if this pre-squaring of the hole would help. What a difference that made!  Not only did this eliminate pin rotation, but pin breakage and leg splitting became rare.

I think the art of drilling holes needs more attention in our craft.  I have watched new employees struggle with basic hole drilling and rarely does a student arrive with a solid understanding of this skill. I’ll get into that in another post. Here, I just want to emphasize the importance of the proper bit type, a Veritas-lipped brad-point, and introduce my favorite drill stop.  The lips of the Veritas bits cut a clean opening and, along with a well-centered point, help keep the bit centered. Before Veritas started offering these bits, I made my own brad-points out of jobber bits because none of the ones I could find had centered points and usually poor-quality steel.  The Veritas bits are fabulous. I have an index of these, keep them away from my other bits, and use them only where I need a joint-quality hole. This helps ensure I don’t wear out the screw holes in plywood.

The wooden depth stop I use makes a big difference, too.  Because it does not spin with the bit, it does not leave a mark on the face of the leg. And just as importantly, it allows me to support the bit directly with my left hand resting against the leg.  This allows me to enter the cut very slowly and with precision.  Even with a great bit, cutting the opening of the hole cleanly makes a big difference. Slow and steady is the way to do that. You’ll notice in the video that I speed up once the opening is cut cleanly. You’ll also see me stop and back up a bit before finishing the hole.  This allows the chips to clear out of the way before letting the stop land against the finished leg.

Once I got this process well-tuned,  I started drilling and pinning after most of the finish was on the chair.  Pins look best when the crisp knife-cut finish is not blurred with the scuffing between coats. It is also nearly impossible to get a perfect finish up against a pin.  In a Berea rocking chair, I was putting in 30 pins total.  Having those out of the way for most of, if not all, of the finishing process, really sped up and improved the finishing. 

Of course, this left no room for sloppy pinning, but I settled on this way of pinning as long as I was the one doing this task. But this leaves two challenges to address: how to trim the pins without leaving knife marks and how to finish the pins without leaving a trace of finishing touch-up yet leaving that fully saturated end grain look on the pin heads.

Many years ago, a good friend, Don Weber, gifted me the best knife I have ever seen for this job. You’ll see me use this in the video.  Don made this knife patterned after the Northwest Tlingit and Haida carving knives. The double edge is a bit treacherous, but I got the hang of it after a few stitches. The pointed tip and rounding of the back sides make it possible to begin a cut on plane with the leg surface and roll up and out in a slicing cut to leave a clean pin finish. Jason Lonon offers these now, but I have not used one of his newer versions. 

The trick with pin trimming is to avoid prying up and bruising the leg. All the pressure needs to be on the pin, not the leg.  That’s a tricky thing to do every time on a rocking chair. It takes me 24 cuts cuts per pin, so that’s 720 cuts that need to not leave a mark. I’m not perfect and have come to accept the occasional subtle knife bruise beside a pin. Only another chairmaker is likely to notice this, and I imagine seeing these little imperfections would be comforting to see rather than offensive.

The last step I did not show in this video is the finish. I have found that thin Stickfast CA glue makes this super quick and easy.  You’ll want to lay the chair down so the pin you are finishing is as perpendicular to the floor as possible. Carefully let one drop slip out the tip with the tip in contact with the pin. Wipe off the excess immediately with a tissue. Tissues will deform very well to the area around the pin and absorb everything that does not get soaked up in the end grain. You’ll want to practice this before doing this on a chair.  It’s important to get a feel for how much to squeeze that little bottle. Be sure to wipe off the tip after every pin; otherwise, dried glue will start to seal the tip.  You also risk gluing the cap onto the bottle if you leave wet glue at the tip.

While the demonstration here shows a rocking chair being pinned, I use this process in cabinet work or anywhere I think a pin improves things.

 I think that covers it.  All you need now is practice! 

Brian