lar portion L for rapid fastening and releasing when in operation. The plate E serves as bushing-plate and bushings as well. It is of tool steel, with three holes at each side as guides when drilling the holes A A A. The holes CC Care countersunk to allow a ready entrance for the drill. The plate is hardened and drawn slightly, after which it is ground on both sides and the holes lapped. The plate is located on the body casting by two flathead screws F and two dowel-pins not shown.

Section of
Clamping
Device

Round

FIG. 57.

When the jig is in use the clamping device is swung out of the way and a pair of castings are located on the jig, dowel-pins DDD being made an easy fit in the cored holes. The swivelclamp is then swung back and the screw K is tightened against the castings, thus fastening the work against the sides of the upright G. The six holes are then drilled. This jig allows of the drilling being accomplished to the required degree of accuracy and interchangeability and in a very rapid manner. The swivelclamp, for fastening the casting against the rib sides, can be adopted to advantage for locating and fastening work of a variety of different shapes, whether the parts are sent to the jig rough or are first machined at different points.

JIG FOR DRILLING AND COUNTERSINKING.

(

The jig shown in Figs. 59-60 was used for drilling and countersinking the holes D in the casting Fig. 58. The castings before being drilled are bored at A to a diameter of 14 inches, and the hub is faced at b b. The hole D is required to be central with the rib C. The parts comprised in the jig are: the body casting, with the circular portion at E, a base at P, and two feet at RR; the bushing R G and the locating and fastening device JIL K and N. The portion E is bored at the front slightly larger than the hub of the work, and is faced at the back for the nut N. The bushing G is hardened and ground and forced into the top. It is lapped to fit a combination drill and countersink. The locating and fastening device consists of a

machine-steel stud with the nut N, and is turned at K to fit a reamed hole at E, and at F to fit the bored hole in the casting.

A half-round groove is let in at L as clearance for the drill. A large head at J and a washer I with a section cut out at M M complete it. The work is located on the jig, so that the hole when drilled will be central with the rib C by entering the rib

into the slot at 0. A slot is let in at Q in the base as clearance for the end of the work.

When in use the washer I is slipped off the locating-stud and

a casting is located. The washer is then slipped over the neck of the stud and the nut N tightened. The hole D in the work is next drilled and countersunk. To remove the work all that is required is to loosen the nut N and slip off the washer.

A JIG FOR DRILLING CAMS.

The cams to be drilled, Fig. 61, were of brass,-inch thick, cut from a bar of 1-inch round stock, the cutting off being done in the monitor. They were to be drilled eccentrically, as shown, with a 1-inch drill. Of course, to drill a hole of this size in pieces so small and have all approximately alike necessitated a jig that would hold them correctly and securely. The jig is shown in Fig. 62, with a top and an end view, the top view with the plate for holding the bushing off. Fig. 63 shows plate and bushing.

A casting was used for the jig proper, with two wings as shown, so that it could be set true and strapped on the drill-table. The bushing-plate was planed on the top and bottom and fastened with four flat-head screws J and two dowel-pins K. A bushing L, of tool-steel, with an 1-inch hole, was then made, hardened, ground, and lapped. The casting, with the plate in position, was then set on the face-plate of the lathe, and a hole 11inch in diameter bored straight through at E. The hole in the plate was then bored out so that the bushing would just drive in. The plate was then removed without disturbing the casting, and a piece of turned steel 1-inch in diameter, with a prick punch mark exactly -inch from the centre, driven into the hole E in the casting tight enough to keep it from turning. The casting was then moved sidewise on the face-plate until the prick punch ran true. The piece of steel was then removed and the hole E rebored to 1 inch in diameter and -inch full, deep; that is, so that the work, Fig. 61, would enter freely. The casting was then removed from the lathe and a slot planed in the way shown at N, Fig. 62; that is, 1 inches wide at the front and running into the

FIG. 61.

hole B as shown. A piece of steel, C,-inch thick, worked out in the way shown to keep the work from being bruised, was then made. A-inch taper hole was drilled in A to admit the lock-pin D, which was of Stub steel, with one flat

side facing the work.

FIG. 62.

The lock-pin and the piece C were both hardened. G is a bracket of sheet steel cut out and bent in the way shown and held by screws II; Fis the knock-out pin, H the spiral spring, and this completed the jig. The plate, Fig. 63, was screwed on and the jig strapped to the drill-table. The work, Fig. 61, was dropped in place, also the piece C, and the lock-pin D was given a tap, which held the work fast. The hole was drilled, the lock-pin removed, and the knock-out hit sharply

with a hammer, causing the work and piece E to come out without any trouble, the spring H bringing the knock-out back in position.

One thing necessary was to have the hole E in the casting and the hole in the bushing exactly the same size as the drill; also

E

J.

the drill ground central, thereby leaving only a very slight burr, as, had it been otherwise, it would have caused trouble in removing the work.

The jigs illustrated and described in this chapter should prove suggestive for the devising of means for the rapid and accurate production of different shaped repetition parts which are to be drilled. One thing which should always be kept in mind when designing or constructing fixtures for interchangeable production is this: the fixtures used for rough or simple shaped castings should, if anything, produce quicker and cheaper than those for machined or perfectly interchangeable ones, because castings of the first type are, as a rule, sold at such a low cost that unless they are produced very rapidly no profit is possible.

FIG. 63.