Fig. 1856.
The heel of the die should not when the cutting edge is in front extend past the axis of the work, but should be cut off so as to terminate at the work axis as denoted by the dotted line g in [Fig. 1856].
Fig. 1857.
In hobbing the dies it is necessary that they be all of equal length so that the hob may cut an equal depth in each, and may, therefore, work steadily and hob them true. After the dies are hobbed their front ends should be reamed with a taper reamer as in [Fig. 1857], chamfering off not more than three threads, and the chamfered teeth must then be filed, just bringing the front edges up to a cutting edge, but filing nothing off them, the reamed chamfer acting as a guide to file them by.
This will cause each tooth to take its proper share of the cut, thus preserving the teeth and causing the dies to cut steadily. Back from the cutting edge towards the heels of the teeth the clearance may gradually increase so that the heel will not meet the work and cause friction.
The chasers or dies are obviously changed for each diameter of bolt, and it follows that as the chasers all fit in the same slots in the head they must all be made of the same size of steel whatever diameter of bolt they are intended to cut, and this leads to the following considerations.
Suppose the capacity of the machine is for bolts between 1⁄4 inch and 11⁄4 inches in diameter, and the size of the chaser or die will be 11⁄4 inches wide and 1⁄2 inch thick.