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Thread: Pitch Diameter Calculations

  1. #1
    Associate Engineer
    Join Date
    Dec 2018

    Pitch Diameter Calculations

    Hi all. I'm new to Engineers Edge Engineering Forum. For many years now, I've been working with helical gears, which sounds greater then my actual experience. For many years we have been cutting our own gears from the print data of designs that were developed and proven back in the 80's. All has gone well until recently. Lately, we have decided to resurrect one of our previous designs. This too is from the proven designs of the 80's. While going through it to confirm the dimensions, I've come to a total stop. Using the formulas in Machinery's Handbook, I can not confirm some gear dimensions. At this time my greatest obstacle is Pitch Diameter. To check my self, I went to the ZakGear calculator. Selecting a pinion we have been producing and using in our gear reducers for years, I pluged in the 'Normal' data. ZakGear agreed completely with the dimension over pins we have been using all these years but agreed with the Transverse Pitch Diameter on the print, not the Normal Pitch Diameter. Thinking our print data is labeled wrong, I go to the Engineers Edge web page about 'Helical Gear and Pinion Equations,' and using the same 'Normal' data, manually calculate for Pitch Diameter. This time D=N/P agrees with the the Normal Pitch diameter on my drawing, not the Transverse Pitch Diameter, as with ZakGear. At this point I am now terribly confused. The Engineers Edge 'Helical Gear and Pinion Equations' (Machinery's Handbook, and ZakGear as well) just say 'Pitch Diameter.' None specify Normal or Transverse. So far, I have always worked under the assumption if it isn't specified 'Transverse' - it is 'Normal.' Now I am no longer sure of that. With all this in mind, I'm not sure of my next step. What precipitated this is the new gear does not specify a Pitch Diameter or Measurement over Pins and Pitch Diameter is necessary for other calculations. All suggestions, ideas, comments any wish to offer will be greatly appreciated. Thanks, K.

  2. #2
    Technical Fellow Kelly_Bramble's Avatar
    Join Date
    Feb 2011
    Bold Springs, GA
    Tell me and I forget. Teach me and I remember. Involve me and I learn.

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