Posted by BillS on June 26, 2013 at 09:13:51:

In Reply to: Lead to degrees formula posted by steve green on June 24, 2013 at 15:56:27:

I use this formula for lead angle of worm to Lead, inch:

Lead = PI x Starts / [ NDP x COS(Lead Angle) ]

So,

Lead Angle = ACOS [PI x Starts / (NDP x LEAD) ]

Where Lead Angle is measured from line perpendicular to worm axis to tangent line at pitch circle as projected onto worm axis.

Not the same as Helix Angle, which is measured from worm axis to tangent line at pitch circle projected onto worm axis. In other words,

Lead Angle + Helix Angle = 90 Deg