The slabbing miller, Fig. 225, is of the planer type, the cross-rail carrying a rigidly supported cutter, while the table has the comparatively slow feed required for milling. This type of machine is especially valuable where broad surfaces are to be machined on pieces of work which are of such shape that they can be readily and uniformly supported to withstand the cut.

. Another milling machine of the planer type, having four spindles, is shown in Fig.226. It is designed for very heavy work.

Especial Care

Necessary to Keep Work True. In order to produce true work by heavy milling, it is not only necessary that the work shall be supported as already outlined, but also that the cut be nearly uniform in depth and width. If the section of the cut varies greatly, or, even with uniform cut, if the work is irregularly supported, the metal will spring under the influence of the cutter, and it will be found that the work is not true. Therefore, work of a character that from its shape is especially liable to be distorted by the process of milling, may be machined to better advantage by the process of planing.

Milling Attachments for Planer

It is often desirable, from the point of view of economy of time, to combine the operations of milling and planing, and, with this end in view, milling attachments are made for the planer in a single machine, Fig. 227, and attached to the cross-rail. The changes required from the planer drive, are an extra belt to rotate the cutter, and a special countershaft to slow down the movemerit of the table. This attachment can carry a slabbing, gang, or formed cutter on an arbor for horizontal milling; or it can carry end mills, Fig. 228, by turning the attached head through 90 degrees, thus bringing the spindle to a vertical position. This last arrangement of the spindle is of great utility, as it allows cutters to reach down into places which would be inaccessible by any other means. Vertical Milling Machines. Vertical Head on Horizontal Machines. The advantages of the vertical milling spindle are so

Fig. 228. End Milling Attachment on Planer.

Fig. 229. Vertical Milling Head Attached to Horizontal Milling Machine.

Courtesy of Brown and Sharpe Manufacturing Company, Providence, Rhode Island evident that nearly all makers of horizontal machines furnish what is called a vertical head, Fig. 229. This vertical head is very rigidly supported on the column by means of the overhanging arm, so that cuts can be taken of as great depth as with the horizontal spindle. The vertical spindle can also be turned in the vertical plane, so that an end mill can be used at any angle with the table.

Vertical Spindles Only

There are several machines made in which the vertical spindle alone is employed, Fig. 230, there being no provision for a horizontal spindle.

Such machines are provided with the feed motions of the horizontal type, and also with a rotating table by which circular work can be done. A large amount of work formerly done in lathes is now being done in vertical spindle machines, as well as many pieces formerly machined on planers and shapers.

Fig. 230. Vertical Milling Machine with Working Parts Shown in Ghost Courtesy of Becker Milling Machine Company, Hyde Park, Massachusetts.

Duplex Milling Machines

The duplex milling machine, Fig. 231, has both the horizontal and vertical spindles combined in one, which allows the spindle to be placed at any angle from horizontal to vertical, and combines all the good points of both machines. The head of the duplex miller can be moved out over the table so as greatly to increase the range of the machine; and this head is also provided with a drilling attachment whereby holes may be drilled at any angle.

Fig. 231. Duplex Milling Machine Set for Cutting Spirals Courtesy of Van Norman Machine Tool Company, Springfield, Massachusetts.