Shaper and Planer. The operation known as milling differs so radically from the removal of metal by methods previously described, that it merits much more careful and lengthy discussion than has been devoted to the other methods. Owing, also, to its increasing importance and general use, it calls for a somewhat detailed discussion. While milling is coming rapidly into favor as a means of doing work formerly done on the shaper and planer, it does not follow that the shaper and planer are to be entirely abandoned. There has been a tendency to belittle the planer and shaper in favor of the milling machine. This tendency is not altogether warranted even by the rapid and economical method of milling. There is a large class of work which can be done as accurately -and in many cases as cheaply-by means of a single-pointed tool such as is used in the planer and shaper.
The fundamental difference between planing and milling lies in the character of the tool employed. The planer uses a fixed single-pointed tool, with a reciprocating motion either of the tool or of the work. Milling is performed by the use of a rotating tool with several cutting points. This rotary multiple cutter is the basis of all milling operations; and, as the saw may be taken as a good example of such a cutter, so the work done by the circular saw in cutting metal may be said to be an example of milling, Fig. 198. The ordinary milling cutter is nothing more than a saw which has exceptionally broad teeth and in which the contour of the cutting blades is made to suit the work in hand.
It was but a step to make a saw wide enough to cover a considerable surface, or to have a thick saw with a suitably formed cutting edge. Several saws of different shapes and sizes can be mounted in a gang on an arbor, and perform operations which it would be hard to duplicate on the shaper or planer. Even in the present age of special machines for milling, a great deal of work of this character is still performed by the method indicated.
Fig. 198. Sawing Flat Stock Courtesy of Brown and Sharpe Manufacturing Company, Providence, Rhode Island.
One of the great advantages of milling is the certainty of exact duplication-a feature of prime importance in the manufacture of interchangeable work.
About the first machine built exclusively for milling was the so-called Lincoln miller, Fig. 199, which consists essentially of a bed carrying the equivalent of the headstock and tailstock of a lathe, with means for rotating the cutter arbor, which is carried directly by the headstock spindle, and steadied and supported by the tail-stock. There is also provided a table upon which the work can be fastened either directly or by means of a vise; and an automatic feed across the machine at right angles to, and below, the cutter arbor. This type of machine in various designs is much used in modern manufacturing.
Fig. 199. Lincoln Milling Machine Courtesy of Pratt and Whitney Company, Hartford, Connecticut.