How does a foot powered mortising machine work?

Answer 1

A true foot powered mortising machine uses a solid chisel, similar to a hand held mortising chisel, to cut a mortise in a wooden member. The machine itself has a foot pedal with a linkage to the chisel that forces the chisel into the wood. The wood is supported on the table of the machine. The pedal is a lever that gives mechanical advantage, multiplying the force exerted on the pedal, so that the downward force on the chisel is much greater than the downward force on the pedal.

The machine is usually about 4' to 6' tall, and stands on a stable base. The chisel holder slides up and down in guides that hold it in vertical alignment. Interchangeable chisels of different widths are used depending on the desired width of the mortise. The wood to be mortised is first marked to show the position and length of the mortise. If a through mortise is desired, the wood is marked on both sides, so the location and size of both the entry and exit are marked. A single hole is then drilled through the center of the mortise, similar to the way you might drill multiple holes that would then be squared up with a hand chisel to make a rectangular mortise. The diameter of the hole is the same as the width of the chisel being used. The wood is then placed on the table of the machine with one face against the fence, and the machine is adjusted so the chisel falls within the marks that describe the sides of the mortise.

The first cut is made by placing the chisel about 1/8" from the side of the hole, and depressing the foot pedal until the chisel cuts about half way through the depth of the mortise. A return spring lifts the chisel back to the starting position after each stroke. The cutting edge of the chisel is at right angles to the fence, so the mortise is cut by moving the wood paralell to the fence about 1/8" at a time between cuts. When the chisel comes to one end of the marked mortise, it is reversed by a small lever with a latch, so the mortise can be elongated in the opposite direction until the other end mark is reached. The same proceedure is repeated from the other side of the wood, cutting out the other half of the depth of the mortise. It is done this way because if the chisel were allowed to cut all the way through on a single stroke, it would cause severe splintering when it exits the bottom side of the wood.

Foot powered mortising machines were invented in the 1830s, and were built by many companies in the last half of the 19th century and first half of the 20th century. They were common in millwork shops where window sash were being built, and also in small cabinet shops. By the 1860s, steam and water powered mortising machines were available, which were an advantage as factories grew in size. There are adherents who still use them in home workshops. There is very little that can go wrong with a foot powered mortising machine.

The terminology sometimes gets confused. Often a power mortiser that is actuated by a foot pedal, will be called a "foot mortiser", but that is different than a "foot powered mortiser".