Page:Practical Treatise on Milling and Milling Machines.djvu/194

188 Milling Screw Machine Cam, Showing Use of Extension for Spiral Head

This shows the milling of a cam of long leads where the blank must be cut well up to the axis in one place. It is impossible to bring the spiral head spindle and the vertical attachment spindle near enough together to accomplish this deep cut when the spiral head is located in its usual position at the end of the table. The extension for the spiral head is designed to overcome this difficulty, and by using it the spiral head is located some distance in from the end of the table.

The cam in this case has three lobes, each having a different lead. Change gears to mill the longest lead are selected and then the angles of elevation of the head and attachment are changed to obtain the shorter leads while using the same change gears.