INTRODUCTION
Milling is the process of removing metal with rotary cutters. It is employed extensively in machine shops today for forming parts of machinery, tools, etc., to required dimensions and shapes. A machine designed especially for this purpose was in existence as early as 1818, but little progress was made in the process until after the invention of the universal milling machine (shown on the opposite page) in 1861-62 by Mr. Joseph R. Brown, of J. R. Brown and Sharpe. This is owing chiefly to the difficulties of obtaining satisfactory cutters and of sharpening them. Shortly after this, however, improvements in the methods of making cutters, the invention by Mr. J. R. Brown of the formed cutter which can be sharpened without changing the cutting contour, and the introduction of the grinding wheel for sharpening cutters removed the obstacles that had so seriously hindered the early development of milling.
As the field of milling widened, the demands upon the machine increased accordingly, and it became necessary to make certain improvements to adapt it to the new conditions. But it is a noteworthy fact that in all of the changes in design leading up to the modern heavy type of universal machine, shown on page 44, none of the fundamental ideas of the original machine have been lost. Parts have been strengthened to better withstand heavier service, and radical changes have been made in the method of driving the spindle and feeds to accomodate the machine to modern requirements.
From a comparison of the original machine with a modern type, the important changes that have been made are readily noted.
The column has been carried well above the spindle, and an overhanging arm with a support for the outer end of cutter arbor has been added. To further stiffen the arbor, arm braces have been devised by the use of which the overhanging arm, cutter arbor, and knee are all rigidly tied together. These braces on the smaller sizes of machines consist of long slotted cross arms, while on the larger, or heavy service machines, a different and heavier type is employed.
