The gage proper may be made of one plate worked to the proper shape, but better results follow if it is made in three pieces, as shown in Fig. 440, on account of the tendency of the plate to spring when hardened. The plates may be made either of tool steel or machine steel. If of tool steel, they should be machined all over and thoroughly annealed, then planed or milled to thickness. One surface should be colored by the blue vitriol solution, or the pieces may be heated until a distinct blue color appears; the desired shape should be marked on the colored surface, and the pieces machined and filed until they fit the model, the necessary degree of accuracy being determined by the nature of the work. Fitting to Base. After]the pieces are properly fitted to the model, they may be attached to the base by means of the fillister head cap screws shown. The model should be laid on the base having the fulcrum screw hole on the pin, and when in its proper location, it may be clamped, as shown in Fig. 442. The sections of the gage, which should have been previously drilled for the screw and dowel pins, may now be clamped to the base in their proper positions. After drilling, the holes in the base may be tapped, and the screws put in place. Slight alterations in any of the shapes are readily made if necessary, as the plates can be moved a trifle since the bodies of the screws need not fit tightly in the holes in the plates. The dowel pinh6les should not be transferred into the base until after the plates are hardened.

Fig. 441. Base Pin for Receiving Gage.

Fig. 442. Model of Gun Hammer Clamped in Place.

Hardening

The plates may now be removed and hardened. If of machine steel, they may be casehardened, and dipped in oil rather than water. If made of tool steel, best results follow if they are pack hardened; they should be run from 1 hour to 1 1/2 hours after becoming red hot, and then dipped in raw linseed oil. If the process of pack hardening cannot be used, satisfactory results may be obtained by heating the plates in a tube in an open fire, or placed in the muffle of a muffle furnace. When red hot sprinkle a small quantity of finely powdered cyanide of potassium, or a little yellow . prussiate of potash, on the contact surface; place it in the fire again; bring it to a low red heat, and plunge it into a bath of oil.

Fig. 443. Locating Gage.

Fig. 444. Piece with Hole to Be Located.

Attaching To Base

After being hardened, the plates may be attached to the base by means of the screws. If any of the gaging points have become distorted during the hardening, they may be brought to the proper shape by oil-stoning. When the plates are properly fitted and located in their exact positions, the dowel pin holes may be transferred into the base and the dowel pins put in place.