Fig. 1240.
Example.—In [Fig. 1240] are a set of change wheels, the first pair of which has a driving wheel having 36 teeth, and a driven wheel having 18 teeth. The second pair has a driving wheel of 66 teeth, and a driven wheel of 48.
Let us begin with the first pair and we have 36 ÷ 18 = 2, and this multiplied by 66 is 132. Then 132 ÷ 48 = 2.75, and 2.75 multiplied by 4 is 11, which is the pitch of thread that will be cut. Now, whether this 11 will be eleven threads per inch, or as in our previous examples a pitch of 11⁄16 inch from one thread to another or to the next one, depends upon what the pitch of the lead screw was measured in.
Fig. 1241.
If it is a pitch of 4 threads per inch, the wheels will cut a thread of 11 per inch, while if it were a thread of 4⁄16 pitch, the thread cut will be 11⁄16 pitch.
Let us now work out the same gears beginning from the lead screw pair, and we have as follows: