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CALCULATING THE HELIX ANGLE
Calculating the helix angle
Example:
Calculate the helix angle ‘a’ for a single start square thread of 85mm outside diameter, core diameter of 60mm and a 25mm pitch.

Core dia. circumference = 3.142 x 60 = 188.52mm
Lead (Pitch) = 25m

Tan a = Side opposite
............Side Adjacent

Tan a = 25 = 0.1326 = (7 dgrees 30 minutes)
 .........188.52

See diagram on right hand side

Calculating tool width
Example:
Calculate tool width ‘X’ when set at 90 degrees to the helix angle 'a' to cut a spiral groove of 12,5mm + 0,05mm clearance, (i.e. 12.55mm).
Cosine a (i.e. 7 degrees 30 minutes) = 0.991 

Cosine a = Side adjacent
.........................Hypotenuse

Cos a = 12.55
 ..................... X

X Cos a = 12.55

X Cos a = 12.55 ..........................X = 12.55 = 12.55 = 12.663mm (Tool width)
.......................................................................Cos a ....)0.991
Tool clearance angles
During the tool grinding process, leading and trailing clearance angles of 6 to 8 degrees are necessary.
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