Helix angle

The thread’s helix angle and cutting tool width must be calculated before tooling up to cut a square thread.

Calculating the helix angle:

1. Draw a vertical line representing the circumference of the thread’s core diameter.
2. Draw a horizontal line representing the lead of the thread from the foot of the vertical line.
3. Draw a straight line joining the two free ends of the vertical and horizontal lines to form a right angle triangle, (see adjacent diagram).

Tool Grinding Elements
For the tool to cut a helical groove of correct size, (i.e. width) a simple calculation is required. The correct tool width is equal to the hypotenuse of a right-angle triangle formed by half the pitch (side adjacent to the helix angle) and the helix angle of the thread.
The need for this calculation is to compensate for the difference in groove width due to feeding the cutting tool into the thread at 90 degrees to its axis, (see diagram below).