# Re: 22 1/2Degs Double Helical Gears

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Posted by John Cerra on October 19, 2007 at 14:13:37:

In Reply to: Re: 22 1/2Degs Double Helical Gears posted by BillS on October 18, 2007 at 12:20:16:

Bill,
It's a visual basic implementation of drgears's base tangent calculation: please tweak it if necessary:

Public Function Span(PA, Helix, Mn, Blash As Double, n As Integer) As Double
' ------------------- Calculate Span Measurement --------------------------------------
' PA=PRESSURE ANGLE, HELIX= HELIX ANGLE, Mn=NORMAL MODULE,Blash= BACKLASH, N=# OF TEETH
' ---------------------------------------------------------------------------------------
Dim an, at, Cavt, avt, Bha, Invat, Wk

an = deg(Atn(TAD)) 'transverse pressure angle in degrees
Invat = inv(deg((at))) 'involute of transverse pressure angle
Cavt = ((n / (n + 2 * 0 * Cos(rad((Helix))))) * Cos(rad((an))))
sn = ((n / PI) * ((Tan((at)) / Cos(rad((Bha))) - 2 * 0 * Tan(rad((PA)))) - Invat) + 0.5) 'opitmal # teeth to span

Wk = (Mn * Cos(rad((PA))) * (((sn - 0.5) * PI) + (n * Invat))) + (2 * 0 * Mn * Sin(rad((PA))))
Span = (Wk / 25.4) - Blash 'convert to decimal and do backlash
End Function

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