Thu 11 Mar 2010
When working with something round, in this case dowels, clamping/holding is always a weird proposition. Round stuff doesn’t like to be clamped. More accurately, clamps don’t like to work on round stuff, at least without resorting to a clamp with rigid grips. In that case you’re likely to crush the dowel at the clamping locations. You can make a frame of some kind to hold your round in place, but then you’ve covered up the areas that you need to work on.
To the left is an appliance/jig that came to me a few days back, for use in cutting a groove with a plow plane. The groove will hold a small strip of hardwood and act as a spring for the dog. More about that later. The appliance is a 1.5″ x 1.5″ chunk of doug-fir with a 3/4″ hole bored into the end. A little less than half of that hole is sawn away, leaving us with a projection of a semi-circle that is just slightly more than half of the circle. This cross section is just right for working with a 3/4″ dowel, as the dowel literally snaps into place from the top, and doesn’t need any more vertical support. As long as the pressure applied is downward, the appliance keeps the dowel from spinning.
At the far end you can see where the hole is stopped. The idea is to saw the shoulder at a depth that more closely matches with the bottom of the hole. This saw cut was a bit low, but it still worked, so I didn’t need to make another.
What we end up with is a channel for the dowel and a clean top (and side) for a plow plane to register against. A groove is cut down the center of the top of the appliance, providing a path and support for the skate of the plane (and the blade) to follow. At this point, lining up the plane with the channel in the top and pushing it against the side of the block allows you to cut a clean groove right down the center of the dowel. I’m sure that a jig can be created for doing this sort of thing with routers and other wood erasers, but doing it this way is downright pleasant. Your mileage will definitely vary.
Cut a cross-grain kerf at the depth of the holding area of the dog and use a shoulder plane to nibble away the waste. I didn’t bother with perfect registration for the plane in this example. In fact, I angled the plane to the left a little to undercut the holding face for better support. I recommend that you consider doing this at about 90 degrees around the dowel from the groove, rather than on the direct opposite side, so the spring doesn’t completely compress when you use the dog. It’s not a deal-breaker, but the dog will more quickly shimmy its way into the hole in this configuration.
My grooves are about 1/8″ deep, and about 1/4″ wide. After ripping a 1/8″ thick strip from a 3/4″ thick piece of scrap I had 3 springs all lined up and ready to be freed from their siblings. For tiny stuff like this I like to use a marking gauge to make cuts. It’s clean, accurate and a lot less fiddly than anything else that I’ve tried. It’s also much, much less dangerous than using machines for small work. Just set the depth of the gauge to 1/4″ and drag the gauge as if you were marking a line. Do this repeatedly, and with more pressure than you might normally use with a marking gauge, and the little wafers will eventually slip right off.
After cutting, the strips are sized and trued a bit using a block plane held upside down in a vise. This is a bit dangerous, but as long as you’re careful you should manage to keep the skin on your knuckles. After a bit of cleanup on the strips, they’re almost ready to glue into the grooves.
The only task remaining is to cut a slight facet at the end, which will be the portion that is glued into the groove. This angle determines how much the spring protrudes from the side of the groove, so it shouldn’t be too severe. Keep in mind that springs are not a part of the clamping operation of the dogs, they really just keep the dogs from falling through the holes in the bench. I placed a sheet of sandpaper on a granite block, tilted one end of the strip up about 15 degrees, and sanded a facet on the end that is about 1/2″ long. Time for glue!
After a bit of glue-up, the extra bit of spring is trimmed from the end, and voila, bench dogs.
The process is really quite simple with the right support. I quickly made a bunch of dogs for the surface of my bench, and a few half-height versions for my vise, as the holes do not go through the entire face. At the worst I will find a flaw in my process and have to build more, but at about 25 cents each, I can quickly, easily and inexpensively do some experimentation.