Calculating True Involute Form Diam Help

[changedsoul]

I am looking to find a formula to calculate TIF.

I am requested show TIF on a report for a bunch of gears we cut. We have software that when you enter the measured data(MOW, root, major, etc) it will display all sorts of wonderful data. The problem is having to do this for so many parts, and the software is not available to the people who are actually checking the parts and documenting the measured data.

So it was proposed to create an excel spread sheet where they could enter their measured data, and the sheet would fill in the rest that needed calculations, such as the TIF.
Best I got was some formulas from the Machinist Hand Book Where its got a very small section and only two formulas:

http://www.nashua.edu/paradisem1/Machinery's Handbook 27th/27_Gears_10.pdf

page 2061.

To my untrained eye, these formulas seem to be independent of any measured data and seems to be based off a standard gear.
Using these formulas to just try and figure this out, I am getting values different than what the software is telling me. I have searched the web for a while and I cant seem to find anything else on this.
Based on the data the software gives, it seems the TIF is dependent on the root diam which makes sense.

Is there a formula I can use to calculate the TIF of a modified gear?

For example, in software
n=28 dp=32 pa=20
mow(.054wires)= .951
root = .7969
fillet R = .010
OD = .9384
With this data, the software calculates a TIF of .829 where as I seem to be getting .8291 ( this is pretty close to standard)
where as with a measured part which has been reduced

mow(.055 wires) = .941
root = .7851
fillet = .010
OD = .932
With this, the software calculates a TIF of .825. I am lost as how to incorporate the profile shift into this calculation.

Any help would be appreciated.
Thanks.

 

[changedsoul]

I think I might have figured it out. If its using the dedendum change to calculate a new dedendum constant, than I guess I got it. If thats not it....I await a responce.

 

[3DDave]

I would recommend getting this book:

https://www.amazon.com/Involute-Curve-Gearing/dp/B000KUJ1VE

The Involute Curve and Involute Gearing 79 pgs
The Fellows Gear Shaper Co.
A complete treatise covering the application of the involute curve to gear teeth,; design, cutting, and checking of involute gears; definitions of gear-tooth elements, etc.

 

[changedsoul]

Thanks for the advise....and its a decent price too.

 

[3DDave]

They were motivated to do a good job. If the people buying their equipment ended up with gears that didn't work, guess who would get blamed. I may have a copy and should probably buy another to be certain, but I don't expect to design any more gears.