Wednesday, February 13, 2008

Sharpening a Plane Blade

At last count, there were exactly 3, 970, 000 ways to sharpen a plane iron. Well, maybe it just seems like that many. The point is, you have lots of techniques from which to choose, and all produce the same result—a sharp blade.

Here are photos showing how I sharpen a newly-made plane iron using a grinder and 800 and 8,000 grit waterstones. Make sure your stones are flat. I flatten mine sometimes twice during a job like this.

Flatten the back of the blade on an 800 grit stone. By gripping a piece of wood on top of the blade, you can apply greater downward pressure than you can with just your fingers. Keep the blade flat as you move it forward and backward on the stone and just concentrate on the 1/2" or 1" that is closest to the cutting edge. Once you have uniform flatness, do the same thing on an 8,000 grit stone until you achieve a mirror polish.

I hadn't sharpened the bevel on this blade completely before heat treating, so it's back to the grinder to finish sharpening before using the waterstones. Here is where you'll want to be sure to dunk the blade in water as you sharpen at the grinder so that you don't overheat the blade. Keep your fingers close to the cutting edge because if it's too hot for you, it's too hot for the blade, and you'll know to quench it.

For safety precautions, always wear a facemask at the grinder and let it run for a minute to warm up before grinding. You should also check to make sure your grinding wheel is not cracked. Do this by removing the wheel, slide a pencil through the center hole so it's suspended without you touching it, and tap it lightly with a plastic handle. It should ring like china. If you hear "thunk", throw it out.

You are finished with the grinder once you can no longer see light reflecting on the cutting edge. Next, secure the blade in a sharpening jig at the same angle you established at the grinder. In this case, 25 degrees. Start with the 800 grit stone and only sharpen on the pull stroke. When you have two flat surfaces on the bevel, move to the 8,000 grit stone without removing it from the jig. Once polished to a mirror finish, angle the blade up about 3 degrees in the jig (with some jigs, you don't have to reposition the blade; you can just turn a knob and it will steepen the angle for you) and create a micro bevel using the 8,000 grit stone only. A micro bevel is not necessary; it's just my preference.

You will now have a small burr on the back of the blade which can be removed with a few laps on the 8,000 grit stone.

You're done! That blade will now shave endgrain, hairy legs, and your neighbor's cat.