Another machine tool which is not used as commonly as its many good qualities would seem to warrant, is the slotter, Fig. 194. It is in reality a shaper with the tool reciprocating vertically instead of horizontally. It is used for working on heavy pieces, and especially in places where an irregular contour is to be formed. The thrust on the tool is vertical, and it and the machine must be very stiff. The work done frequently partakes of the nature of forming the inside of a hole where the tool must project the whole length of the cut below the bottom of the head. Such a case is that of the slotting of locomotive frames. The best type of tool for such a class of work is a strong bar, as shown in Fig. 195. The bar is held in the tool head just as any tool would be. Near the lower end, it carries the cutting tool, which may be fastened by a set screw or wedge. Such a tool should always be used when it is possible. It has the advantage of being stiffer and less likely to spring than a common forged tool.
The tool used in a slotting machine differs from that used in the lathe or planer, in that the direction of the cutting motion is different. Fig. 196 illustrates a slotting tool used for doing such work as the cutting of keyways in the hubs of pulleys. It will be seen that if the tool is moved in the direction of the arrow, the face B becomes the one against which the chip bears. It therefore corresponds to the top of the lathe tool. The sharper the slope given to the face B, the keener the edge, just as increasing the top rake of the lathe tool increases its sharpness. The face A must also be cut away as indicated. This corresponds to the clearance of the lathe or planer tool. It is quite possible, at times, to give these tools a larger amount of rake. Such a form is shown in Fig. 197. The shape of these tools is such that they are very strong in the direction of the thrust, besides having a keen cutting edge.
The slotter has automatic feeds of three kinds-namely, lateral, transverse, and circular-hence a considerable variety of work can be done upon it. The stroke of the vertical ram which carries the tool can be made any length of cut from zero to full stroke, and its location with relation to the work table can be adjusted according to the height of the work to be done. Like the shaper, it has a quick return after the cutting stroke, and it is provided with four changes of speed. This renders it available for quite a large range of work.
HEAVY UNIVERSAL MILLING MACHINE.
Courtesy of Brown and Sharpe Manufacturing Company, Providence, Rhode Island.