How to Sharpen and Use Mortice Chisels

In this video Matthew Platt of Woodwork Heaven shows how to sharpen a mortice chisel and then in an excellent demonstration that follows he shows how to chisel out a mortice for a mortice and tenon joint. His demo shows what actually happens “inside” the mortice as you are cutting it.

The mortice chisel has three cutting edges. The bade has a bevel that is angled at 30 degrees, this serves as the primary cutting edge. Also the two sides should be ground flat producing a sharp cutting edge where the side meets the back.  As  the chisel is driven into the wood the bevel pushes it forward.   This forward movement help produce a clean and smooth cut to the sides of the joint.

 The back and bevel are sharpened as with a normal chisel. A guide is used to keep the blade at the correct angle.  Matthew recommends the Richard Kell no. 1 or no.2 guide and it looks like he uses wet and dry abrasive on a sheet of float glass.

The difference between mortice chisels and other woodworking chisels is the sides of the bevel are sharpened.  This is done by laying the side of the chisel on the grinding surface and applying pressure with the fingers over the length of the blade but  over the edge where the side and the back meet.  This process is repeated on both sides.