Fig. 1742.
In these forms of tube plate cutters it is necessary to drill a hole to receive the pin d. But this necessity may be removed by means of a cutter, such as shown in [Fig. 1742], which is given simply as a representative of a class of such cutters. a is a cutter stock having the two cutters b b fitted in slots and bolted to it. c is a spiral spring inserted in a hole in a and pressing upon the pin d, which has a conical point. The work is provided with a deep centre-punch mark denoting the centre of the hole to be cut. The point of d projects slightly beyond the cutting edges of the cutters, and as it enters the centre-punch mark in the work it forms a guide point to steady the cutters as they rotate. As the cutters are fed to their cut, the pin d simply compresses the spiral spring c and passes further up the cutter stock. Thus the point of d serves instead of a hole and pin guide.
Fig. 1743.
A simple form of adjustable cutter is shown in [Figs. 1743] and [1744]. It consists of a stock a a with the shank b, made tapering to fit the socket of a boring or drilling machine. Through the body of the stock is a keyway or slot, in which is placed the cutter c, provided in the centre of the upper edge with a notch or recess. Into this slot fits the end of the piece d, which is pivoted upon the pin e. The radial edge of d has female worm teeth upon it. f is a worm screw in gear with the radial edge of d. Upon the outer end of f is a square projection to receive a handle, and it is obvious that by revolving the screw f, the cutter c will be moved through the slot in the stock, and hence the size of the circle which the cutter will describe in a revolution of the stock a may be determined by operating the screw f. Thus the tool is adjustable for different sizes of work, while it is rigidly held to any size without any tendency whatever either to slip or alter its form. The pin g is not an absolutely necessary part of the tool, but it is a valuable addition, as it steadies the tool. This is necessary when the spindle of the machine in which it is used has play in the bearings, which is very often the case with boring and drilling machines. The use of g is to act as a guide fixed in the table upon which the work is held, to prevent the tool from springing away from the cut, and hence enabling it to do much smoother work. It is usual to make the width of the cutter c to suit some piece of work of which there is a large quantity to do, because when the cutter is in the centre of the stock both edges may perform cutting duty; in which case the tool can be fed to the cut twice as fast as when the cutter is used for an increased diameter, and one cutting edge only is operative. The tool may be put between the lathe centres and revolved, the work being fastened to the lathe saddle. In this way it is exceedingly useful in cutting out plain cores in half-core boxes.
