While drilling dog holes in my new maple benchtop, I realized that 3/4 in. is the tap drill size for a 1/2-in. pipe thread. After drilling the dog holes to size, I tapped them with a 1/2-in. pipe tap, going deeper than the normal thread depth for a pipe to give the threads more holding strength in wood. This allowed me to screw a threaded section of 1/2-in.-dia. pipe into the tapped dog hole and, in turn, screw a pipe-clamp head to the pipe's other end. I've been using this setup for two years now, and the tapped wooden threads in the hard maple have held up just fine in their double duty as dog hole and threaded insert.

 Pipe Clamp Workbench

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I use the threaded dog holes in three ways: First, I can install a clamp perpendicular to the benchtop in any dog hole to use as a hold-down. Second, after drilling and tapping holes in the apron of the bench, I can use a clamp as a side vise against a dog. Finally, utilizing drilled and tapped holes on the opposite side of the apron, I can attach the quick-release end of the pipe clamp. This lets me hold items that are wider than the benchtop.

The tapped holes on the side of my bench are really neat. It is like having an extra vise. You can screw a short or long pipe into the hole. The arrangement gives a lot of latitude for clamping. When locating the side holes, it is important to put them at the correct height below the top of the bench. Too low and the clamp head will not be above the top of the bench.

Drawings by Jim Richey , ,
July 21, 2009