Page:Practical Treatise on Milling and Milling Machines.djvu/20

 on page 13, but in addition is designed so that the spindle is more powerfully driven and has a greater vertical adjustment. The table is also provided with a transverse movement. This machine is therefore adapted to a somewhat wider range of work than thte one previously described.

The planer milling machine is designed for the heaviest classes of slab and gang milling. It bears a marked resemblance to the planer, from which it derives its name. The spindle is mounted in bearings carried in a vertically adjustable slide similar to that of a planer, and the table is in a corresponding position This brief reference will enable one to easily distinguish these machines. And, as the class of work performed is identical in character, only heavier than that done on the column and knee type of machine, the same principles are involved.

Returning to the column and knee type, we can subdivide it into three classes, known as Plain, Universal, and Vertical Spindle Machines.* In the first two the spindle is supported in horizontal bearings that are fixed in the main casting of the machine instead of being adjustable vertically, as in hte case of both manufacturing and planer types of machines. This is one of the points where the column and knee machine is radically different from either of the other types. As we have already explained, vertical adjustment in this type is obtained by the movement of the knee upon the column. In the vertical spindle machine, the spindle is supported invertical bearings, verticle adjustment being obtained by the movement of both the knee and the spindle.

Plain Milling Machine. The word plain when applied to any milling machine is used to designate one in which the longitudinal travel of the table is fixed at right angles to the spindle. Both manufacturing and planer types are therefore essentially plain milling machines.

An illustration of a plain milling machine of the column and knee type is shown on page 19. In this machine, the table has the three movements: longitudinally, transversely, and vertically, that have already been mentioned. Some machines have both power and hand feeds for all three of the movements; others have longitudinal and transverse movements so controlled and the vertical is operated by hand; or the longitudinal movement alone is operated both by power and by hand, and the transverse and