The chasers are numbered to their places and are so constructed that if a single chaser of a set of three should require renewal, a chaser can be obtained from the manufacturers that will match with the remaining two of the set, the threads on the one falling exactly in line with those on the other two, whereas in other dies the renewal of one chaser involves the renewal of the whole number contained in the die. This is accomplished by so threading the dies that the thread starts from the same chaser (as No. 1) in each set.
Fig. 1819.
In [Fig. 1819] is represented one of these machines, which is intended for threads from 3⁄8 to 1 inch in diameter. It is arranged to be driven by belt power, being provided with a pulley having three steps; on this pulley spindle is a pinion operating a gear-wheel on the die driving spindle, as shown.
The oil and cuttings fall into a trough provided in the bed of the machine, but the oil drains through a strainer into the cylindrical receiver shown beneath the bed, whence it may be drawn off and used over again.
Fig. 1820.
In [Fig. 1820] is represented a bolt threading machine which is designed for bolts from 3⁄16 to 1 inch in diameter.