Page:Practical Treatise on Milling and Milling Machines.djvu/186

180 Fig. 72

As a .196" lead is much less than .67", which is the shortest lead regularly obtainable on the milling machine, (see Table of Leads, pages 229 to 247), the change gears that will give a lead of .67" may be used, and then the angle of the head can be adjusted so that a lead of .196" will be obtained on the cam lobe with these change gears. The rule for this is:

Divide the given lead of the cam lobe by a lead obtainable on the machine, and the result is the sine of the angle at which to set the head.

Continuing the calculation for the lobe of the cam in Fig. 72, we therefore have: $.196"⁄.67$=.29253

Hence, .29253 is the sine of the correct angle. Turning to the Table of sines and cosines on pages 300 to 308, we find that .29253 is very