I got an answer to my question about second-hand plane purchasing that talks about making an infill plan. What is an infill plane and how is it different than a basic hand plane?
On basic appearance it looks similar to a block plane.
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The body of a typical hand plane is a single metal casting. An infill plane, by contrast, is formed from metal plates (sole and sides) joined along the edges, or sometimes by a single piece of metal U-channel. Dense wood is used to fill the space between the plates to support the sides, establish a bed for the iron, and to make holding the plane possible.
Infill planes are often made with steep blade angles, which makes them work well on highly figured woods. They can be and often are made one at a time by woodworkers for their own use in a wood shop with only basic metalworking tools. The metal components can be cut by hand or ordered as a kit, and are usually joined with soldered dovetail or box joints.
Most types of hand planes can be made as infill planes: block planes, smooth planes, jack planes, shoulder planes, etc. can all be made as infill planes.
An infill plane is basically a metal plane with a wooden core. It's common to take an existing metal-bodied plane and add wooden components to make an infill plane.
In the example given in the referenced answer, if the metal-bodied plane's mouth is badly damaged you can cut the plane into two pieces along the mouth, trim back the metal so you have clean edges, and add new sides of wood or metal to hold the front and back together.