The Complete Handbook of Mortisers

Chapter 1: Understanding Mortisers

A mortiser is a machine tool designed to cut square or rectangular holes into wood with precision and repeatability. At its core, it combines two mechanical actions: a vertical drill-like spindle that holds a hollow chisel and auger, and a horizontal, reciprocating table that drives the wood toward the cutting tool. The hollow chisel surrounds an auger, or spiral bit, that removes the waste material from the center of the hole. As the table moves the wood upward into the chisel, the auger pulls the waste out of the hole and deposits it on the table surface or into a dust collection system. When the stroke reaches its maximum depth, the table springs downward, the chisel retracts, and the process repeats for the next hole or the next pass in a series of overlapping holes.

This is not the same as using a drill press. A drill press holds the wood stationary and brings the rotating bit downward into it; a mortiser holds the tool stationary and brings the wood upward into it. A drill press with a standard twist bit will produce a round hole; the waste comes out as you drill, and the hole enlarges as you go deeper. A mortiser with a hollow chisel and auger produces a square hole with crisp, flat-bottomed edges in a single pass or a series of precisely spaced passes. The wood enters the chisel from below, the auger cuts and removes waste, and the chisel walls cleanly