As I get ready to make prototypes of various components of the Krenov cabinet I shared with you a short while back, I realized my mortise chisels needed some care. As I prepared the 1/4-inch chisel, it occurred to me that it was an opportunity to share with you how I tune my chisels, to make it more pleasurable to use them on the mortising machine. On the left is the cabinet I used to determine if I could develop a working model of a Krenov-style cabinet in eCabinet Systems software – I am modifying this model into a design I will build.
The procedure I use to tune the chisels is not new, and it is very simple if the “proper” tools are used to create a sharp edge. This is how I do it:
- I use the Rockler 3-piece mortise sharpening set – it comes with two diamond-covered abrasive cones that put a nice bevel on the inside surface of the tip of the chisel – for the smaller 1/4 inch chisel I prefer to use the cones on the drill press. It is essential to use speeds lower than 300 RPM, to prevent glazing of the abrasive surfaces on the cones:
3-Piece Mortise Chisel Sharpening Set
- Remove the machine marks on the outer surfaces of the chisel. This will give a better finish on the face of the mortise. It also helps the chisel to slide smoothly as it makes the cut. I do it using 150-grit sandpaper on a smooth and flat surface, such as the cast iron on the table saw. Always use the same number of strokes: 20 to 30 strokes should be sufficient.
- Finally, remove the burrs that form on the very tip of the chisel, using a diamond stone. I like to use 10 strokes to remove the burr.
That is all – you should have a nice, sharp chisel to allow you to make the mortices without overheating the chisel tips. If you keep them sharp, you will prevent overheating and burning; overheating is likely to make your mortise-making experience miserable.
You can read a good article by Bob Lang of Popular Woodworking here. I have not used a file to notch the inside corners of the chisels, as Bob does. I will try this if I run into chip-clearing issues in the future.