DRILLING-JIG FOR DOVETAILED SLIDE-BRACKETS.

A separate and distinct type of jig for heavy work is shown in the three views in Figs. 94-95. It is used for drilling all the holes in the dovetailed slide-bracket shown in Figs. 96-97, and, as will at once be seen, can be located on the work simply and

rapidly. The bracket (Figs. 96, 97) has four holes drilled at V V V V and two at W W. The four holes V are for fastening the bracket to the body of the machine of which it forms a part, and those at W W for fastening a spindle-bearing to the portion on the bracket. The casting, before being drilled, is machined on the back at U, planed dovetailed at SS, and a cut is taken off the top at TT. The dovetailed surface is utilized as the positive locating-point for the jig, as it is shown secured in the work in the two views of Fig. 95. The bottom of the jig and the point Z are finished to coincide with the dovetailed surface of the work. The angular-faced clamp A is forced up against the work by the two set-screws B B and drawn up tight by the clamping-lever and stud C. The end locating-point is at D, which consists of a flat steel plate fastened to the overhanging end of the jig by two flat-head screws. The four bushings F F project down almost to the face of the jig, this being necessary, as the casting at this point is not machined. When being drilled, the casting rests on the back X and the jig is located and fast

ened on it as shown in Fig. 95. The holes drilled, the jig is quickly removed by loosening the two set-screws B B and the clamping-lever C, which allows the clamp A to be slid back and

the jig removed. The design of this jig gives a practical illustration of how simple and inexpensive tools for the drilling of heavy parts can be constructed, by choosing the most adaptable locating-points on the work, and designing the jig castings so as to have as few points as possible to machine. When locating and finishing the bushing-holes in this jig, it was first finished at all points necessary, and then clamped to the slide-bracket, or work, which was in turn clamped to the miller-table, with the top of the jig up.

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The holes were then located and finished by getting the distances from the machined surfaces of the work and using the vertical attachment, thus doing away with the necessity of first laying out the holes on the work, then finding their location in the jig. This is a very good plan to follow when the shape of the jig castings will not allow of their easy fastening to the miller-table. Moreover, in getting the distances between the bushing-holes, the machined surfaces of the work are reliable points to measure from.

FIG. 97.

DRILLING-JIG FOR POWER-PRESS BOLSTERS.

Fig. 99 shows still another jig, in two views. It is for drilling all the holes in the press-bolster shown in Fig. 98. The casting, as can be seen, is a rather difficult one to handle; but by the

use of the jig the drilling is accomplished with ease and expedition. The only finishing done on the casting before drilling, is to plane all sides of the two oblong projections, as shown at A A,

B B, and C C, to gauge. The holes drilled are the four DDDD and two E E, and one through each of the projections FFFF. The jig (Fig. 99) is in two parts, the lid and body casting.

The

as shown in the plan view, by the locating-spots C I and H and the set-screws K K and J; the large strap L holding it securely in the bottom of the jig. The lid is located by the two nuts 0 0. The bushings N through each of the projecting lugs on the face of the lid, are for the holes through FF FF in the work. four bushings R are for the holes D and those at Q Q for the holes E E. When the jig is in use the work is located and fastened within it, as shown by the dotted lines in the plan view in Fig. 99. It is then rested on its back and all the holes in the face are drilled. The holes in the projecting lugs of the casting at Fare drilled by standing the jig on each of its sides in turn and drilling down through the bushings N. In this jig the amount of time taken to locate, fasten, and then drill the work amounts to very little when the shape and bulk of the casting is considered. Jigs of this design can be used to the best advantage for the drilling of heavy castings on which are a number of projecting lugs, and when holes are drilled in them to a given line, or in line with each other, as in the case of the casting drilled in this one.

POINTS TO BE REMEMBERED.

In constructing tools of the class described in this chapter a few things must be considered: first, to construct the tools as simple as possible and to make them positive, so that they can be handled by cheap help without the possibility of going wrong. Also, in choosing locating-points on the work for the jigs, take the same ones (wherever possible) for all succeeding operations, thereby eliminating, as far as possible, the margin of error which may be the result of preceding operations. For instance, let us consider the upper columns of drill-presses: The first operation on such parts is the planing of the angular faces of the colThese faces are then used as locating- and truing-points for the succeeding operations of milling and drilling. Therefore, if, when the columns were set upon the planer for the first operation, they were not set square with the ends, the error was overcome in the machining of the ends in the next operation. Another thing, tools of the kind shown should always be made as strong as possible, so as to withstand rough usage without in

If the tools are delicate, the

any way affecting their accuracy. time wasted in caring and looking after them offsets that saved in the machining of the work by their use. Also have a place for fixtures where they may be put out of the way when not in use; do not have them encumbering the floor, as is all too frequently the case in a number of shops. This will tend to lengthen their life, and it will not be necessary to hunt all over the shop whenever they are wanted.