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This is a marking knife I made for a friend, William Walker (check out his channel here). A marking knife is a very useful tool for woodworking. Often times a pencil line is too thick for fine woodworking, and pencil lines are almost always slightly offset from what you are marking against. 

A marking knife leaves a very thin cut that is easy to place right against a surface. A bonus of the cut is it is easy to register a chisel edge in it for precise paring.

This marking knife was made from an old file that was about 1/8" thick. The first step was removing the heat treating from it by heating it up and then letting it cool slowly, that process is called annealing.

After the metal has been annealed, it is pretty easy to work with normal grinding wheels, cut off discs, and files. After the shaping is complete it is important to heat treat the metal again, otherwise the metal will not be harden enough to hold a sharp edge.

The process differs depending on the metal being used, but basically it must be heated past the point where it losses magnetism and then quenched in oil or water. The problem with really hard metal though is that it is brittle, any hard impact will cause it to chip or crack.

To make the metal less brittle it must be tempered. To temper metal it is heated to a relatively low temperature and allowed to cool slowly.

 After heating treating and tempering the metal will be very dirty looking, but that is fairly easy to remove with sanding. After running through the grits and sharpening the metal should be at a good polish.

For the handle I used a piece of lignum vitae left over from another project. I cut it to rough size on the bandsaw and then roughed out a slot for the blade on the bandsaw.

A file the same size as the file the blade was made from worked well to finish cutting the slot to the perfect size for the blade. The blade was fit with epoxy and two brass pins. After it was all together I used my belt sander and a file to shape the handle.

I finished it with three coats of paste wax.It did come out looking a bit more like a dagger than a marking knife, but this is only the second knife I have made and it cuts a fine line.