Wednesday, May 13, 2009

Learning to Sharpen Chisels

Let's face it, I never started out to be a hand tool guy. There is something about power tools that just draws me to them. Among other things, they have (for me, at least) a mystique about being precise in application. Though I'm finding out they are only as precise as their user, still, the whole idea of hand tools leaves me with the impression of their being susceptible to misuse by my unpracticed hands.

Be that as it may, I have already found chisels handy enough (OK, essential) that I broke down and bought a set. I didn't pop for an expensive set but instead caught Woodcraft's Wood River brand when it was on sale. What I didn't count on was the fact that while they are not exactly dull when they arrive, they do need a basic sharpening to make them really useful.

The first thing I did was purchase a basic grinder, which is needed to shape the front of the blade. But after asking my friend Jeff Fleisher how to sharpen them properly, he put me on to an article about David Charlesworth's method. Finally, today I drove out to his shop in New Market, Virginia, and he helped me sharpen the first chisel so I could see and experience the process for myself.

The process is fairly straightforward, if a little tedious when doing it for the first time. Charlesworth's method calls for a series of Japanese waterstones. You first flatten the back (flat) side of the chisel to remove all the tooling marks as it comes from the factory. This involves working the back of the chisel up and down and then back and forth on either a 200 grit stone or wet or dry sandpaper laid wet on a sheet of glass. When the factory marks have been removed, only slight scratches from the stone or sandpaper should remain. You then move to a 1200 grit stone that has been wetted and repeat the procedure, working from there to a 4000 grit stone and finally an 8000 grit stone on which a slurry has been made with a nagura stone. By the time this has been done, few if any scratches should remain and the back of the chisel should be both flat and scratch free.

The next step is to work on the beveled side of the chisel blade. Here you turn to the fine wheel on a slow grinder. You mark the beveled edge with a Sharpie, then grind away the marked metal, holding the chisel at precisely 90 degrees to the wheel. When all the marking has been ground away, you should have a slightly concave surface on the bevel.

The final stage is to put a fine edge on the chisel. This is done on the 8000 grit stone using a device that holds the chisel blade at 30 degrees to the stone. Five or six pulls is all that is needed. Then you increase the angle slightly and repeat the process, again five or six times. All that's left now is to check and see if there's a burr on the flat side of the chisel and, if so, remove it by pulling the blade across the stone a few times.

The finished blade should be able to cut the top of your fingernail when gently pushed against it or should be able to shave a piece of soft wood like pine smoothly and cleanly.

So, I now have one sharp chisel. And a lot of work to do to get the rest of them ready for real use. The good news is, once the backs are flattened (the slow part of the process), I should not need to do more than touch up the bevels for a long time to come!


1 comment:

  1. Nice article...there is one step that you forgot. After grinding, you use the honing guide with the 1200 grit stone first at 30 degrees, and then followed by the 8000 grit stone at about 32 degrees. In the end, Charlesworth uses three different angles...he grinds at 25 degrees, initial honing at 30 degrees with 1200 grit, and polish microbevel at 32 degrees. --Jeff