Page:Practical Treatise on Milling and Milling Machines.djvu/254

248 TABLES OF LEADS FOR CAM LOBES Obtained with Spiral Head and a Vertical Spindle Milling Attachment Set at an Angle

The method of using the Spiral Head and a Vertical Spindle Milling Attachment for cutting the lobes of cams is described in Chapter IX, and the following tables have been worked out to enable the machine to be set up without the necessity of figuring the leads and settings.

In compiling these tables, we have employed the same combinations of change gears as those in the "Table of Approximate Angles for Cutting Spirals," all of which will reach without interfering. The practical leads obtainable with each set of change gears have been grouped together so that when a machine is set for any lead, and it is desired to change to another lead, the operator can quickly determine whether the required lead is available without changing the gears already on. As this is often the case in this work, the saving in time that is effected is readily appreciated.

A selection of cam leads from to 20" is listed, and it should be understood that these are the leads or amount of rise in a complete circle, not the amount of rise of a lobe in a fractional part of the circumference. From the amount of rise of the lobe it will be necessary before using these tables to calculate the lead or rise if the lobe were continued the full circumference. This is easily found as explained on page 179.

In using these tables to set up a machine to mill any required lead, the column under the heading "Approximate Lead" is first followed down until the range of leads is found which embraces the required one. Then follow the horizontal line across until the nearest dimension to the exact lead required is found. At the top of the column containing this dimension will be found the required combination of change gears, and in the next two columns at the right, and in line with the dimension selected, will be found the angles at which to set the spiral head and vertical milling attachment.

Example: Required, the change gears and angles at which to set the spiral head and vertical milling attachment to cut a cam with a lead of .1476".