CHAPTER VI.

The Design and Construction of Drilling-Jigs for Heavy Machine Parts, etc.

CONSTRUCTING LARGE DRILLING-JIGS.

THE introduction of tools and fixtures for the production of duplicate parts of heavy machinery and tools has necessitated the devising of means and the designing of fixtures by the use of which the part, or parts, to be machined could be handled with ease and expedition. The result has been that where the proper design and construction of fixtures has been carried out, the finished work has proved vastly superior to that done by the old methods.

In designing and constructing drill-jigs for heavy parts there are a number of obstacles to be met and overcome, not found in jigs for the different classes of work shown and described in the preceding chapters. They are in effect as follows: In the increased size and strength of the jig castings. Then in the locating- and fastening-points for the work, which must be so situated as to allow the work to be located and fastened within the jig quickly, with the least exertion on the part of the operator. Lastly in the locating and finishing of the drill bushing-holes, which cannot (as a rule) be successfully accomplished by the same means used in the construction of jigs for small parts.

JIG FOR DRILLING A NAILING-MACHINE CROSSHEAD.

The numerous and various jigs shown in the accompanying illustrations show clearly the most practical design and construcsion for the various shaped castings shown. In Fig. 86 are three views of a cast-iron cross-head for a nailing-machine. This is finished at three points, at A A, B B, and the bottom C C. The

holes drilled are eighteen in number; four at each end at D; four at E, and six at F in the front projection. The jig for drilling them is shown clearly with the work fastened within it in the two views in Fig. 87. It consists of one casting with legs at each

end at G G. The work is located by forcing it endwise against the two locators I and H respectively, by the set-screws L L (see view, Fig. 88). Four straps, KKKK, fasten and hold down the work securely on two raised and finished spots in the bottom of

the jig. The bushing-holes are located and finished by the method described in the beginning of this chapter. When in use the work is fastened within the jig by slipping it down on the locating-points and tightening all screws and clamps. The jig is

then stood on end on the legs G G and the holes are drilled through the bushings Q Q, after which it is reversed and the holes in the opposite end drilled through the bushings PP. The large holes through the four projections are then finished by inserting a boring-bar through the bushings O and the cored holes in the four projecting lugs of the cross-head, in which four cutters are fastened, one end of the cutter-bar being fastened in the drill-press spindle, and the other end running in and passing through the hole in the centre of the table, as the bar is fed down. The jig is, as simple as possible, and allows the work being very rapidly located, fastened, drilled, and removed.

The

projecting lugs on the sides for the straps or clamps K K K K strengthen the ends of the jig, and overcome the tendency to weakness in the projecting ends. The use of a boring-bar with four cutters for finishing the holes E, Fig. 86, is both economical and productive of good results, saving time in the finishing of the holes and insuring their alignment with each other when finished. The use of the clamps for fastening the work tends to the rapid fastening and releasing of the same, as by a single turn of the nuts they can be swung on or off.

DRILLING-JIG FOR CAST-IRON IMPRESSION ROLLERS.

In the two views of the cast-iron impression roller in Figs. 89, 90, we have a piece of work that would be difficult to handle without the use of a jig. The roller is turned and finished in the

lathe and then transferred to the miller and indexed for six, and the four channels T T T T are milled down its entire length. In each of these channels six holes, R, are drilled and in the plain

side of the roller four counterbored holes, W, are let in. The inside of the roller is cored out as shown by the dotted lines, with cored vents at V V. A 2-inch hole through the ends at UU acts as a journal-bearing for a revolving shaft. The jig is clearly shown in the cross-sectional view in Fig. 91, and in the top and end views of Figs. 92, 93. X is the main casting, Y the bushing-plate, and I the shaft on which the roller Z to be drilled is fastened. The locating-plate C revolves in the end B of the jig and projects through to the opposite side, the index-plate P being keyed to it at G and fastened by the nut H. The bushings Nare for the six holes R in the channels, and those at M for the counterbored holes W W, Fig. 90. To locate the roller within the jig so that the channels in which the holes are drilled will be in line with the bushings, the locator D is used. It is fastened within a channel in C by the cap-screw shown, piece

D fitting the channel E snugly, as shown in the cross-section; while the roller is fastened to the shaft I by the set-screws K.

In the end view of the jig, Fig. 92, the indexing-holes in the plate Fare shown-those for the holes in the channels are at RRR, and the one into which the index-pin J is entered, four

in all. That for the counterbored holes is at Q. The top view of the jig shows the position in which the bushings N and M are located, and the manner of locating the bushing-plate by the four

FIG. 92.

screws L and the two dowel-pins P P. By reverting to Fig. 91, the manipulation of the jig when in use, and the drilling of the work will be understood. The shaft I and the roller Z are inserted, fitting between the locating-plate C and the finished hub on the end A, with the locator D in the first of the channels. The shaft I is then slipped through and set-screw K in the roller tightened. The jig is then set on the table of a large adjustable multiple spindle-drill; six of the spindles being set so that the drills will enter the six bushings N, and four of the remaining spindles so set that the counterbores will enter the bushings M. The jig is then fastened securely to the press table by cap-screws through the ends at C. The four holes W (Fig. 84) are then counterbored, first removing the drills from the other six spindles. The counterbores are then removed, the six drills refastened to the spindles, and the index-plate revolved until the first channel in the work is under the bushing N. Index-pin J is now entered and the six holes drilled, when the index-plate is moved for the next channel and the holes drilled in it, the holes in the

remaining two channels being drilled in the same manner. The use of this jig together with the multiple spindle-drill makes the handling and drilling of the heavy roller a simple operation, that would, however, be difficult to perform satisfactorily by any other means. Moreover, the work produced will be found to interchange perfectly.