Flattening the Sole

Firstly, for a plane to work well, the sole must be perfectly flat. Some planes will arrive from the factory with a flat sole, but most hand planes need serious abrading to flatten the sole. If your plane sole is twisted, which often occurs naturally as the metal acclimates to the ambient temperature after casting and/or mill work by the factory has been completed, you must flatten the sole, otherwise the plane will be unstable and rock as you use it. The most common faults affecting how a plane functions for creating a flat surface, lie in the flatness of the sole. If the plane is hollow or round, the plane will create an exact opposite: A hollow plane sole will create a round on the surface being planed, conversely a round plane sole will create a hollow. Either of these two faults will make it impossible to create a truly flat and straight surface.

Radical Preparation

To make the sole flat is a simple process and should take only a short time. Spray adhesive some aluminum oxide abrasive paper to a flat surface; a tablesaw table will work well. You can also use 1/4” plate glass or a slab of granite. Use a coarse abrasive paper for the initial flattening and, when the sole is flat, use a series of increasingly finer abrasive papers to further polish the sole. It’s not necessary to go beyond #120-grit abrasive paper, though of course you can if you want to.

High
spots

The whole sole
becomes shiny
after flattening
After abrading for a period on a truly flat surface, the whole of the sole will become shiny as the high spots are levelled to the lowest point of the lowest hollow.
To check whether the sole is hollow, round, uneven or twisted, pass the sole of the plane over the abrasive paper a couple of times. Any high spots will show as shiny steel.