By changing these two wheels any fraction of a pick can be obtained. Thus if 13½ picks per quarter-inch are required, the wheels used would be an 18 standard and a 27 change wheel. For 13⅔ picks a 27 standard and a 41 change wheel would be used, and so on.
The following examples will fully illustrate the principle of this motion:—
Picks per quarter-inch.
Standard wheel.
Change wheel.
20
9
20
15½
18