Pinch Dogs to the Rescue (I Hope)
Like pocket screws, traditional pinch dogs are a great way to join odd assemblies or to use them in conjunction with clamps. A typical use is to drive them into the ends of a panel while the woodworker uses a bar clamp to secure the middle. (The middle is typically sprung, but that’s another entry.)
Pinch dogs come in a lot of shapes and sizes, but they are essentially a pair of conjoined steel wedges. You hammer the tips of the wedges into the two adjacent surfaces you want to join. The two wedges pull the joint tight.
They work great. Or rather, they used to work great. No, the laws, of simple mechanics haven’t been suspended. But I’ll get back to this point in a bit.
Today I used pinch dogs to pull together the two pieces of an arm for a stick chair. As these arm pieces are curved and covered in compound angles, a simple clamp wouldn’t do the job without some additional fussing.
So I applied glue to the two mating surfaces and pressed them together. Then I clamped one part to my bench (this prevents the parts from sliding around when you hammer in the pinch dogs). I drove the first pinch dog through the centerline of the joint to try to keep the pressure even throughout the joint. That worked fine, but I decided to use a second pinch dog at the rear of the arm to pinch this visible area a little more.
After the glue dried, I removed the excess adhesive, turned the armbow over (with great care) and glued on the center piece of the arm that connects the two arms – sometimes called the “doubler” because it doubles the thickness of the arm.
About These Shiny Dogs
I had to put off assembling the arm for several days because I couldn’t find my old set of pinch dogs. They were black and had a rough surface texture. From what I remember of them, they were likely cast ductile iron.
Because I couldn’t find the old dogs, I bought a new set. These were shiny – likely covered in zinc or some other smooth coating. As a result of the coating, these dogs tended to pop out of the wood – more like “pinch prairie dogs” than real pinch dogs. After some really hard hits, however, I got them to stay.
Still, I was miffed. So I threw the pinch dogs into a ceramic container with some citric acid, which safely removes zinc. If that acid takes the zinc off I’m going to encourage the dogs to rust, which shouldn’t be difficult in our humid Ohio River Valley.
That, I hope, will fix my dogs so they do their old tricks.
— Christopher Schwarz
P.S. If you don’t want to strip the coating off new dogs, try buying pinch dogs off ebay. They are cheap and easy to find.