Machinery's Handbook - 6: Thread Depth and Compound Angle WARNING: Machine tools present a safety hazard. Improper operation can result in severe injury. These topics are for non-laboratory study only and are not to be used in conjunction with the operation of any tool or machine described herein. Never use a machine tool without the supervision of a qualified instructor. To cut the material on a conventional engine lathe: Find how much to feed in for a complete thread. Again, turn to the table in the Unified screw threads chapter and find the pitch diameter for the 1-8UNC-2A thread....the pitch diameter must be between .9168 and .91 the average value will be (.9168 + .91) /2 = .9134 Assuming that the major diameter is .990 a feed in of 990 - .9134 = .0766 is required. Note: thread geometry is controlled by four things: Pitch, major diameter, pitch diameter, and thread angle. The minor diameter is a byproduct of these. So a feed of .0766 will produce some minor diameter that is not shown in the graphic above. Preparation to machine the thread is almost complete. However the compound slide is set to 29 degrees. How many thousandths must the compound be moved to achieve the .0766 depth required? A right angle must be solved. To solve a right angle triangle for this problem turn to the solution of right angle triangles page of the Machinery's Handbook. Since the compound slide is set at 29 degrees the formula shown must be used to find out how much to feed on the compound slide: The distance to dial in is .0766 and the angle of the compound is 29 degrees so you can arbitrarily assign .0766 to side b and 29 to angle A. The formula to use is c = b/cosA In this case c = .0766/cos29 = .0875" label: machiney's Handbook., blueprint, steel properties, speed and feeds, threads, measuremennt, over wires, press fits, slip fits