Fig. 1384.

Between two lugs, b and b′, it receives the end of arm a. These lugs are provided with set-screws, the distance between the ends of which regulate the amount of movement of the end of arm a. Upon a is the slide d, carrying the piece e, in which is the marking tool f, the latter being lifted by a spring g, and, therefore, having no contact with the wheel surface until the spring is depressed. h is an opening through the arm a to permit the marking tool f to meet the wheel face, as shown in [Fig. 1384], which is an end view of the slide showing the arm a in section. The face of the wheel rests upon the chuck on each side of the arm at the points i, j, and may be clamped thereto by the clamps k. The arm may be clamped to the wheel by the clamp shown dotted in at l, the bolt passing up and through the screw handle m. n is simply a lever with which to move the arm a, or arm a and the wheel. Suppose all the parts to be in the position shown in the cuts, the clamps being all tightened up, the slide d may be moved forward towards k, while the spring is depressed, and f will mark a line upon the wheel. The handle m may then be released and arm a moved until it touches the set-screw in b′, when m may be tightened and another line marked. Clamps k are then tightened, and the wheel, with the arm a fast to it, moved back to the position shown in the cut, when the clamps may be tightened again and another line marked, the process being continued all round the wheel. To detect and enable the correction of any discoverable error in a division, there is provided the plate p, having upon it three lines of division (which have been marked simultaneously with three of the lines marked on the wheel). This plate is supported by an arm or bracket q, on the rear edge of which are three notches r to hold a microscope, by means of which the lines on p may be compared with those on the wheel face, so that if any discrepancy should appear it may be determined which line is in error. The labor involved in the operation of marking a large wheel is very great. Suppose, for example, that a wheel has 200 lines of division, and that after going round the wheel as described it is found that the last division is 100th inch out; then in each division the error is the two-hundredth part of this 100th inch, and that is all the alteration that must be made in the distance between set-screws b and b′.

VOL. I.DIVIDING ENGINE AND MICROMETER.PLATE XV.
Fig. 1385.
Fig. 1386.Fig. 1387.
Fig. 1388.Fig. 1389.
Fig. 1390.Fig. 1391.

[Figs. 1385] and [1386] represent a method of originating an index wheel, adopted by R. Hoe and Co., of New York City.

In this method the plan was adopted of fitting round a wheel 180 tapering blocks, which should form a complete and perfect circle. These blocks were to serve the same purpose as is ordinarily accomplished by holes perforated on the face of an index wheel. In their construction, means of correcting any errors that might be found, without the necessity of throwing away any portion of the work done, would also be provided. Further, this means would provide for taking up wear, should any occur in the course of time, and thus restore the original truth of the wheel.

[Fig. 1385] of the engravings shows the originating wheel mounted upon a machine or cutting engine. Upon the opposite end of the shaft is the worm-wheel in the process of cutting. After the master worm-wheel has been thus prepared by means of the originating wheel, it is used upon the front end of the shaft, in the position now occupied by the originating wheel, and operated by a worm in the usual manner. Subdivisions are made by change wheels. The construction of the originating wheel will be understood by the smaller engravings.

[Fig. 1386] is an enlarged section of a segment of the wheel, while [Fig. 1387] is an edge view of this segment. [Fig. 1388] is a view of one of the blocks employed in the construction of the wheel, drawn to full size.

In the rim of the originating wheel there was turned a shoulder, c, [Fig. 1387], 5 feet in diameter. Upon this shoulder there were clamped 180 blocks, of the character shown in [Fig. 1386], as indicated by the section, [Fig. 1387]. These blocks were secured to the face of the wheel d by screws e, and were held down to the shoulder by the screw and clamp g f, shown in [Fig. 1387]. (They are omitted in [Fig. 1385] for clearness of illustration.) In the preparation of these blocks each was fitted to a template t, in [Fig. 1388], and was provided with a recess b, to save trouble in fitting and to insure each block seating firmly on the shoulder c. The shoulder, after successive trials, was finally reduced to such a diameter that the last block exactly filled the space left for it when it was fully seated on the shoulder c. The wheel thus prepared was mounted on a Whitworth cutting engine, as shown in [Fig. 1385]. The general process of using this wheel is as follows: The blocks forming the periphery of the originating wheel are used in place of the holes ordinarily seen in the index plates. One of them is removed to receive a tongue, shown in the centre of [Fig. 1385], which, exactly filling the opening or notch thus made, holds the wheel firmly in place. After a tooth has been cut in the master worm-wheel, shown at the back of [Fig. 1385], the block in the edge of the originating wheel corresponding to the next tooth to be cut is removed. The tongue is withdrawn from the first notch, the wheel is revolved, and the tongue is inserted in the second position. The block first removed is then replaced, and the cutting proceeds as before. This operation is repeated until all the teeth in the master wheel have been cut. The space being a taper, the tongue holds the originating wheel more firmly than is possible by means of cylindrical pins fitting into holes. The number of blocks in the originating wheel being 180, the teeth cut in the master wheel may be 180 or some exact divisor of this number.