Posted by BillS on May 27, 2013 at 08:05:22:
In Reply to: Re: Span measurement posted by Sandesh on May 23, 2013 at 23:30:45:
This paper includes span measurement formulas, and is very clearly written. I believe the span formulas you seek are shown in formulas  thru  on page 2.
The involute function in formula  is the definition of involute angle u which is equal to 9 used in formula . Involute angle 9 (or u) must be implicitly solved since there is no direct formula for involute angle.
You will need to decide how you want to resolve the involute angle for . There are different ways to do that, since it is commonly used for many different gearing relationships. Just Google for "involute function."
Also, I thought the article would be interesting to others since it presents three ways to find helix angle of a sample gear based on span measurements and over pin measurements. One of the procedures presented can be used to find helix angle of an internal gear.
Simple Techniques for Measuring the Base Helix Angle of Involute Gears by C. Innocenti, University of Modena and Reggio Emilia, Modena, Italy
Would there be any interest in having a web page here that would automate these procedures to find helix angles? And that would
include some field testing by an interested shop to proof the accuracy, etc. Plus I would just need some span and over pin measurements, plus
gear specs to test the web page. Seems like a useful addition to the other page that calculates span measurement.
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