Sharpening a Chisel

I have unreasonable sentimentality about Stanley Model 40 chisels. I started buying them about 30 years ago just as they were being discontinued. They seem to sharpen easily and hold a good edge. I was always missing the one inch chisel and recently was lucky enough to find one on eBay.

Step 1: Beat Up Chisel Handle

When I received it, I noticed that the back of the handle had been hit pretty hard over the years.

Step 2: Badly Sharpened Bevel

When you saw the bevel, it was no surprise that someone had hit it that hard. It looks like it had been sharpened multiple times but each sharpening had only added another facet to the bevel.

All chisels, whether new from the factory or used, need tuning before they work well.

Step 3: Reason #1 for Sharpening

The primary reason to sharpen a chisel is shown in this photograph. You can see how poorly the chisel cut a piece of softwood and all I was trying to do was pare a small piece off the corner. The chisel crushes the fibers until they break rather than cutting them.

Step 4: Reason #2 for Sharpening

And there’s a second less obvious reason. For 35 years, I have carried a reminder on my left palm of the dangers of working with a dull chisel.

Step 5: The Back of the Chisel

Ideally, you want to have two perfectly smooth surfaces, the bevel and the back, meet to form the cutting edge. Any imperfections in either will reduce the sharpness of the chisel.

Here’s the chisel back when I received it. You can still see the machine grinding marks left from the factory.

Step 6: Flattening the Back

The most overlooked part of tuning a chisel is flattening and polishing the back.  The easiest way I’ve found to do this uses sandpaper and a piece of plate glass. Using a spray bottle, I spray water on the back of a sheet off sandpaper which usually creates enough suction to have it adhere to the glass. Depending on the condition of the chisel, I’ll choose the appropriate grit but generally I start with 80 grit open coat silicon carbide sandpaper. I move the chisel back and forth (along the long axis of the chisel), keeping the back, flat against the paper, until the marks on the back are consistent across the surface.

Step 7: Refining the Back

I usually use 80, 120, 150 and 220 sandpaper. After all, I only have to do this the first time I sharpen a chisel. Use each grit moving the chisel until you get a consistent pattern

Step 8: Polishing the Back

After using sandpaper, I polish the back with a set of Japanese water stones.

I end with an 8000 grit waterstone or when I run out of time or patience

Step 9: Hollow Grinding the Bevel

After flattening and polishing the back, I grind the bevel. My favorite tool for doing it is a water cooled large diameter grindstone. It turns slowly and leaves a beautiful finish. You can also do it on a regular grinder but you have to be very careful not to overheat the tool and lose the temper of the steel.

I apply pressure very close to the edge of the tool and use a jig to ensure that the edge of the blade stays square

Step 10: Honing the Bevel

I use a 4000 grit water stone to hone the bevel.  I apply pressure close to the edge and use my other fingers to support the weight of the chisel. I start by setting the back of the bevel on the stone and slowly rocking it forward until the tip of the chisel touches the stone. One of the primary advantages of the hollow grind is that the chisel almost locks into place because there are only two points of contact

I gently pull back on the chisel four or five times and look for the small bevel forming at the two points of contact. Once I’m happy with the bevel, I finish up with an 8000 grit stone to polish the bevel.

I’ve tried various jigs over the years to hone the bevel but I find most of them way too fussy for me. If you have trouble doing it by hand, there are some good jigs commercially available.

Step 11: Testing for Sharpness

There are many ways to test for sharpness. You can gently use the chisel on your fingernail, try to cut a piece of paper or if you have the means, try shaving the hair on your arms.

After a while, it’s easy to know whether the chisel is really sharp by just (carefully) running your finger across the edge

Step 12: The Real Test

The real test is whether it cuts wood cleanly. Test it on the edge of a block of wood. A piece of softwood requires a sharper chisel than hardwood to cut cleanly

Step 13: Oil the Chisel

Finally, dry the chisel and put a light coat of camellia oil (tea seed oil) on the chisel. It’s an edible non-toxic oil that helps prevent rusting.

When the chisel gets dull, you can just hone and polish the bevel. After five or six times, you’ll have to touch it up on a grinding wheel before honing