For this very important addition to the engine take a piece of wood
three inches wide and two inches thick. Saw it on _both_ sides to a
point (_fig. 7_). First shave it down on top so that it forms a sharp
point at _b_, _fig. 7_. Then draw a line through the middle of the
top (_a_ to _b_, _fig. 7_), and shave down each side so that it shall
present a sharp edge all around from _c_ to _b_, and from _b_ to _d_
(_fig. 7_). Nail this to the front end of the platform board with
inch-long brads.