Anonymous

“ If two or more rows of holes are to be drilled parallel, the guide block can be drilled accordingly, so that the different rows of holes can be finished at the same time. The drill guide block should be relieved slightly in the center so as to insure the ends of the block bearing against the edge of the scale. A toolmaker or machinist can drill a row of holes accurately by this simple method, in the time required to lay them out in the usual way, and even though accuracy is not necessary, it is quicker to drill holes by this method than by the one more commonly employed. ”

“ Locating Holes
The accuracy of work done by the button method previously described is limited only by the skill and painstaking care of the workman, but setting the buttons requires a great deal of time. By a little modification, using what is sometimes called the “disk-and-button method,” a large part of this time can be saved without any sacrifice of accuracy. The disk-and-button method is extensively used in many shops. Buttons are used, but they are located in the centers of disks of whatever diameters are necessary to give the required locations. ”

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“ When an accurate indexing or dividing wheel is required on a machine, the method of securing accurate divisions of the circle illustrated at C, Fig. 22, is sometimes employed. There is a series of circular disks or bushings equal in number to the divisions required, and these disks are all in contact with each other and with a circular boss or shoulder on the plate to which they are attached. The space between adjacent disks is used to accurately locate the dividing wheel, engagement being made with a suitable latch or indexing device. ”

“ Another method which can at times be employed for accurately locating a jig-plate in different positions on an angle-plate, is shown in Fig. 29. The angle-plate is, of course, set at right angles to the spindle and depth gages and size blocks are used for measuring directly the amount of adjustment. Both the angle-plate and work should have finished surfaces on two sides at right angles to each other, from which measurements can be taken. ”

“ Care should be taken to have the gibs on all sides fairly tight at the beginning, and these should not be tightened after each consecutive alignment, as this generally throws the work out a few thousandths. If the reductions in the size of the plug, each time it is turned, are confusing, new plugs can be used each time a test is made, or the end of the original plug can be cut off so that it can be turned to the same diameter for every test. If the center distances x are not given, it is, of course, far more convenient to make all the geometric calculations before starting to work. ”

“ The only part of the milling machine on which dependence must be placed for accuracy is the hole in the spindle, and this is less liable to get out of truth, from wear such as would impair the accuracy, than are the knee, table, or micrometer screws. The only moving part is the sector, and this, being light, is very sensitive. ”

“ Sometimes it is necessary to machine a number of holes in a plate so that all the holes are on a circle or equi-distant from a central point, and also the same distance apart, within very small limits. A simple method of spacing holes equally is illustrated at A, Fig. 22. A number of buttons equal to the number of holes required are ground and lapped to exactly the same diameter, preferably by mounting them all on an arbor and finishing them at the same time. ”

“ As the work being operated on is brought nearer to the proper location by the movements of the milling machine table, spring G will be compressed, the center rod sliding back into barrel L. This spring is made so that it will hold the center against the work firmly, but without interfering with the free rotation of the sector C around disk D. When the work is located so that the plug enters the holes, the gibs of the machine should be tightened up and the plug tried once more, to make sure that the knee of the machine has not moved sufficiently to cause the work on the table to be out of line. ”

“ As the center-to-center distance between adjacent holes is 2 inches, slides A and B would be set so that the dimension x equals 2 inches plus the radii of the bushings. A straightedge is then clamped to the work in such position that a close-fitting plug can be inserted through the end holes which were previously drilled or bored. Then with a plug inserted through, say, bushing B and one of the end holes, the first hole is drilled and reamed through bushing A; the jig is then shifted to the left until the plug in B enters the hole just made. ”

“ Measurements across accurately lapped plugs in the holes, showed the greatest deviation from truth to be 0.0002 inch, and running from that to accuracy so great that no error was measurable. This same work with buttons would have required considerably more time.
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“ As will be seen, an ordinary combination square is used in connection with a disk, the head of the square being set at different points on the blade according to the angle that is desired. Theoretically, a one-inch disk could be used for all angles from about 6 degrees up to a right angle, but in practice it is more convenient and accurate to employ larger disks for the larger angles. ”

“ While it is desirable to have disks of tool steel, hardened and ground, or, in the larger sizes, of machine steel, case-hardened and ground, a disk for occasional use will be entirely satisfactory if left soft.
Another example of work is shown in Fig. 10. This is a jig templet similar to the one illustrated in Figs. 6 and 7. Sketch A gives its dimensions and sketch B shows the disk-and-button way of locating the holes. A steel square is clamped with its stock against the right-hand edge of the templet and its blade extending across the top. ”

“ For instance, if holes were to be bored in the casting for a jig templet which had simply been planed on the top and bottom, the casting could be bolted to a finished plate having square edges and the latter be set in the different positions required, by means of size blocks. Comparatively large jig plates are sometimes located for boring in this way and the milling machine is often used instead of a lathe. ”

“ The sizing of the outer diameter of the bushing, which was 1.158 inch, must be done so accurately that it was not thought wise to trust to the ordinary micrometer caliper. An indexing device was therefore made having a calipering lever with a long end, in the ratio of 10 to 1, which actuated the plunger of a dial test indicator of the well-known type made by the Waltham Watch Tool Co. The thousandth graduations on the dial of this indicator would then read in ten-thousandths, permitting readings to be taken to one-half or one-quarter of this amount. ”

“ On some jig work, sufficient accuracy could be obtained by using the feed-screw dials alone, that is, without testing with the plugs, in which case the accuracy would naturally depend largely on the condition of the machine. ”

“ The size-block method is usually applied to work having accurately machined edges, although a part having edges which are of a rough or irregular shape can be located by this method, if it is mounted on an auxiliary plate having accurately finished square edges. ”

“ The work is commonly held to the master-plate by means of clamps and tap bolts or by screws which pass through the work and into the master-plate. Solder is sometimes used when it is not convenient to hold the work by clamps or screws.
Fig. 17. Master-plate applied to a Bench Lathe Faceplate
The plug P which locates the master-plate, is first turned to fit the spindle or collet of the lathe and the outer or projecting end is roughturned for the holes in the master-plate, which should all be finished to exactly the same diameter. ”

“ Toolmakers and machinists occasionally find it necessary to locate a number of equally-spaced holes on a straight line between two points, or to divide a circle with holes which are equi-distant within a very small limit of accuracy. Several dividing and spacing methods are described in this chapter ”

“ The mechanical engineer, machine designer and draftsman are also well provided for in Machinery. Every number contains articles on the theory and practice of machine design, on the properties of materials, and on labor-saving methods and systems. ”

“ In this case, the center button was first located correctly from the sides and end and then the other buttons were set. When doing precision work of this kind, the degree of accuracy obtained will depend upon the instruments used, the judgment and skill of the workman, and the care exercised. A good general rule to follow when locating bushings or buttons is to use the method which is the most direct and which requires the least number of measurements, in order to prevent an accumulation of errors. ”

“ The dividing wheel, the construction of which has just been described, was made by the Fellows Gear Shaper Co. It is used for indexing the Fellows gear cutters in the machine in which the teeth are ground. The indexing mechanism of this machine is shown in Fig. 24. It is operated by a handle or lever pinned to rock-shaft H, to which is keyed arm J. Pivoted to J is a pawl K engaging the teeth of ratchet L, which revolves loosely on shaft H. This ratchet L controls the movement of locking finger E. The parts are shown in their normal or locked position in the engraving. ”

“ This is composed of common rosin and plaster of paris and is made as follows: Heat the rosin in a vessel until it flows freely, and then add plaster of paris and keep stirring the mixture. Care should be taken not to make the mixture too stiff. ”

“ The ring is then clamped and the hole is [Pg 26] partly reamed, the reamer being inserted far enough to finish the hole in plate e and also cut clear around in the upper part of plate f. One of the taper pins is then driven into this hole and then a hole on the opposite side is partly reamed, after which the other pin is inserted. ”