Page:Practical Treatise on Milling and Milling Machines.djvu/18

12 thus enabling vertical cuts to be taken. Provision is made for movement of the table horizontally in two directions: one, longitudinally, at right angles to the axis of the spindle; and the other, transversely, parallel to the axis of the spindle. The combination of these three movements is found only in the column and knee machine, and it is due to the advantages derived from this construction that the machine is superior to the manufacturing or planer type for general milling purposes.

Several more illustrations of column and knee machines are shown on succeeding pages of this chapter, where a further classification is given.

This type of milling machine is shown in the illustration on the opposite page. It is a development of one of the earliest forms that was built particularly for use in the manufacture of small parts of firearms, and has since been successfully adopted for machining parts of sewing machines, typewriters and other machines and tools. The advantages it offers for this class of work are due to the stiff construction and convenience with which it can be operated. These make possible an exceptionally large production of first quality work—factors of great importance in commercial manufacturing.

There are many minor variations of this type of milling machine, but the general features are similar in all. in that shown on the opposite page, the spindle is supported in bearings located in an adjustable head that can be raised and lowered. The capacity of the machine is rather limited as regards work of widely varying heights. Furthermore, there is no transverse table feed, the only movement transversely being obtained by a slight adjustment of the spindle. These, however, cannot be considered disadvantages, as provision for work of widely varying heights is not required, because all work done is of comparatively small dimensions, and there is seldom any necessity for a transverse table movement.

The longitudinal movement of the table is at right angles to the axis of the spindle. This movement is accomplished either automatically or by hand by means of a rack and pinion on the under side of the table. The pinion is driven from the spindle through a train of change gears and a worm and wheel when the automatic feed is in action.

A larger and improved style of manufacturing machine is shown on page 88. It embodies all features of the machine illustrated