Thursday, October 7, 2010

Brass Pins For a Krenov Plane

Brass has been an important component in woodshops for years. It’s warm glow peeks out in old plane depth adjuster knobs, wear strips on marking gauges, and binding old levels. It’s kind to tool steel, and patinas beautifully. It works easily with carbide tooling, and is easy to machine even if you don’t have a milling machine or metal lathe.

I’ve made Krenov style planes before, so to change things up I wanted to try making the pin in brass. I started by picking up a 12” long, ½” diameter rod, which cost me about $14.

I started by cutting one end square on the miter saw. It’s important to clamp any round stock, be it metal or wood. It’s too easy for the saw to catch the piece and spin it when it’s held by hand. Also, a miter saws forces go back and up, your clamps pressure must be exerted above the rods centre line. This forces the rod against the fence and down toward the table. In the photo below, you can see the rod, held by a block slightly raised above the table. The block is being pressured by the clamp, also fairly high. A spacer, thicker than the rod, puts the blocks pressure on the rod close to where the cutting happens. Then I measure, mark, and cut the rod 1/8” longer than the plane will be wide.

Next, I cut tenons on the ends. These are 1/16” shorter than the plane cheeks are wide, 3/8” in diameter. To make them I use a carbide spiral bit in my router and I use a wood guide. The block is milled square, and a centre line is layed out on its face and across the end. A sharp ½” brad point bit is used to drill the pilot holes for the bit and the brass. The router base is bolted directly to the block, and the whole jig is clamped in the vise. The rod is chucked into a drill and the router switched on. The feed rate is controlled by two things, the rate of plunge and the rpms of the drill. Keep both low for best results. Surface finish is markedly better if you were to approach the router from the opposite side; the cut is cleaner when the ends of the flutes do the work. The problem with that is the amount removed from the diameter of the rod is dictated by the offset of the holes drilled and there is no adjustability. Because the tenon sides are hidden by the plane cheeks, surface finish isn’t important, so I prefer to do it in this manner. Coming at the bit from its side allows you to tweak both dimensions, tenon diameter by varying the depth of the router bit, length of tenon by the depth of rod penetration. The drill chuck acts as a stop, so once I get the right length of tenon I measure the amount protruding from the chuck and do the rest with the same.

From there it’s to the drill press to dress and dome the ends. The rod is chucked up by the tenon to avoid marring the visible surface. I lower it against sandpaper backed by a foam sponge. The soft backing allows the faster moving circumference of the rod to wear quicker than the middle, resulting in a domed end. I use 120 grit paper to remove the saw marks, then it’s polished to 600. The pin will be 1/16” proud of the cheeks when done, so I strive to have the domes edge meet that mark. I do one end, and then I flip the pin and do the other. While it’s chucked up and spinning, I use the sandpaper to polish the rod itself.

Next, a flat is milled into the pin to match the wood wedge used to hold the blade secure. A simple jig is made to hold the pin; a 3/8” hole drilled in the same place in two wood blocks receives the tenon. Both blocks are brad nailed to a piece of plywood to keep them in the same plane, and the jig is clamped in a vise, further securing the hold. A steel screw is countersunk below the surface, its tip biting the tenon and preventing the pin from spinning. A bushing is installed in the router to leave a 1/8” between the flat and the tenon shoulder. The flat is 1/16” wider than the plane blade. The router is placed on the jig, the bit lowered until it’s touching the pin. The router is started, and using a slow feed rate passed back and forth over the pin until the span has been covered. Now the flat is measured. If it is not the same on both ends it is because the pin isn’t parallel to the top of the jig. Shim the side with the wider flat with duct tape, lower the bit until it’s touching the wide end, and try again. Once the flat is even I cut it to a depth of 1/16”.


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I'm a woodworker on the Canadian prairie.