RE: [CAD_CAM_EDM_DRO] Helix Angle

You'll be soooo pleased to know that the helix angle of the thread tip
and root are not the same!
To see how to calculate the angle, imagine a piece of paper wrapped
around the appropriate diameter (root or tip or anywhere in between). If
you trace the helix to the paper, along with a circumference line
(straight around) and one lengthwise, then unwrap the paper and flatten
in. The three lines will (if you connected them right) form a triangle.
The line that was the lengthwise one will be the thread lead distance.
The line that was the circumference will have a length equal to the
circumference (duh!).
These two lines form a right angle.
The hypoteneuse is the helix line. The tangent of its angle will be the
thread lead divided by the circumference.
Thus for the thread tip, the angle will be arctan(0.125/(pi*0.7087)),
which is 3.2134 degrees.
For the thread root the angle will be
arctan(0.125/(pi*(0.7087-0.125*tan(60)))), which is 4.6217 degrees.

Although I'm not sure why you need this to generate a CAD model for the
helix...
-Kevin Martin
-----Original Message-----
From: Terry Owens [mailto:terry@...]
[...]
This may at first sight appaer to be off-topic but it isn't. I nned to
know the answer so I can draw it in CAD to make a part for a CNC
machine.