07-30-2012, 07:33 AM
Helix angle is a function of pitch and diameter. What is the major diameter? If say, a 6TPI was on a 12" OD part, the helix angle would be much lower than on a 1" diameter. Just a example. Think of the helix angle as the smaller of the two angles adjacent to the hypotenuse of the wedge geometry if you took a single thread path of one revolution and "unwound" it to a flat surface. You get a triangle, right? That's all a thread is. A long wedge wrapped around a stick. Tightening a bolt in a nut is like pushing two wedges together and getting a force along the axis of the two that draws them tight. Clear as mud, yes?
I'd expect to see a 6 pitch on something no less than 1 3/8". The helix angle is calculated along the pitch line. Formula is:
HA = arctan(L/((OD+MD)*3.141/2))
HA is Helix Angle
L is Lead
OD is Outside Diameter
MD is Minor Diameter
For example, on my 1.375, the HA is 2.2095°. You can use the calculator here to check your math, or do it for you.
http://www.americanmachinist.com/calcula...tting.aspx
If you have 10°, you have plenty of clearance.
I'd expect to see a 6 pitch on something no less than 1 3/8". The helix angle is calculated along the pitch line. Formula is:
HA = arctan(L/((OD+MD)*3.141/2))
HA is Helix Angle
L is Lead
OD is Outside Diameter
MD is Minor Diameter
For example, on my 1.375, the HA is 2.2095°. You can use the calculator here to check your math, or do it for you.
http://www.americanmachinist.com/calcula...tting.aspx
If you have 10°, you have plenty of clearance.