Fig. 317.
In [Fig. 317] is shown Everett’s stocks and dies. In this tool the dies are set up by a cam lever, the dies being set to standard size when the lever arm stands parallel with the arm of the stock. By turning the straight side of the cam lever opposite to the dies, the latter may be instantly removed and another size of die inserted. The dies may be used to cut on their passage up and down the bolt or by operating the cam. When the dies are at the end of a cut the dies may be opened, lifted to the top of the work and another cut taken, thus saving the time necessary to wind the stock back. When the final cut is taken the dies may be opened and lifted off the work.
The hardening process usually increases the thickness of these dies, making the pitch of the thread coarser. The amount of expansion due to hardening is variable, but increases with the thickness of the die. The hob as a rule shortens during the tempering, but the amount being variable, no rule for its quantity can be given.[12]
[12] See also [page 108].
Fig. 318.
Stocks and dies for pipe work are made in the form shown in [Fig. 318], in which b is the stock having the detachable handles (for ease of conveyance) a, h, the latter being shown detached. The solid screw-cutting dies c are placed in the square recess at b, and are secured in b by the cap d, which swings over (upon its pivoted end as a centre) and is locked by the thumbscrew e. To guide the stocks and cause them to cut a true thread, the bushes f are provided. These fit into the lower end of b and are locked in position by four set screws g. The bores of the bushes f are made an easy fit to the outside of the pipe to be threaded, there being a separate bush for each size of pipe.