used. A chain with cutters (similar to a chainsaw chain) rotating within a frame clamped to the work is successively plunged into the workpiece to mortise out the required volume. The Makita 7104L is such a tool. These chains are made in varying widths, with numbers of chains in parallel. The teeth are often solid or tipped tungsten carbide. They are thus very expensive, sometimes as much as the rest of the mortiser. Other methods of cutting mortises Traditionally, a mortise would be cut by hand, using a chisel and mallet. However, due to the precision of fit required for a mortise and tenon joint, this can be a difficult and time-consuming task. Other tools such as a router could be used for the task, but the router usually requires special attachments, jigs or templates and the router bit leaves rounded corners that might need to be squared by hand with a chisel. Alternatively, the tenon can be rounded with a rasp to achieve an equally strong joint. For cutting small mortises, a normal drill bit can be used. However, for larger mortises, a common type of bit in modern mortisers is a Harry Watt square drill bit, in which a bit with a Reuleaux triangle cross section is allowed to "wobble" while it rotates within a square with rounded corners. This type of bit removes all but the corners of the material to be removed, leaving very little to be cut by the chisel. See also Rotary broaching, a method of drilling square holes in steel. External links History of the Greenlee Company - includes the history of the mortiser Reuleaux triangle on MathWorld - includes an animation of the action of a Harry Watt square drill bit Woodworking machines Timber framing