Page:Practical Treatise on Milling and Milling Machines.djvu/30

 made from high speed steel, for they can be made to take unusually heavy cuts at fast speeds and coarse feeds. It is impossible to eliminate all vibrations from even the very best types of machine construction, but they may be reduced to a minimun, or, in orther words, to a point where they will not affect the accuracy of the work, if every part is so constructed that it is capable of resisting heavy stresses, and absorbing vibrations. Weight and well-proportioned construction are most necessary to overcome vibrations.



Knee of Brown & Sharp Milling Machine illustrating the points mentioned opposite

The essentials in the design and construction of the column and knee machine that serve well to illustrate the general points that conduce to rigidity in all machines, follow:

First, the base must be large and heavy enough to provide a firm foundation, and the walls of teh column must be thikc and strongly braced, in order to support rigidly the weight of the working parts and withstand the strains of operation. Especially is this true of the front wall, which forms the basis of support for the table. If this is not heavy enough and well braced, it will have a tendency to buckle under the heavy loads it is required to support, which will not only admit of vibrations, but also destroy the alignments of the machine. Another point in connection with this front wall, or vertical slide, is that it should be wide in proportion to the size of the machine, as the wider a flat bearing, the more stable it is.

All shafts should be of large enough diameter to resist bending and torsional stresses, and gears should be of ample size to give