Page:Practical Treatise on Milling and Milling Machines.djvu/29

 must be ample to easily support the weight brought upon them. The accuracy of alignments can be ascertained upon first operation of a machine, but their permanency can be determined only after a considerable period of service.

Rigidity. This requirement is of just as great importance to the success of a milling machine as correct alignments. Any machine tool must be rigid in order to produce accurate, well finished work;

'''Brown & Sharpe Milling Machine, showing large base, thick walls and internal bracing. The spindle bearings are mounted directly in thick walls of column.'''

the milling machine must be particularly so. It is not until within the past few years, however, that the real value of this essential has been fully appreciate. This is owing to the fact that up to that time the milling machine had not become so extensively used for manufacturing purposes. In this field it must be capable of not only producing accurate work of high quality, but of producing it rapidly. The more rapidly a machine is operated, the greater is its tendency to vibrate. This is further augmented by the use of cutters