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  1. #1
    5thwheel is offline Stainless
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    Question What is gear pitch?

    In searching gear catalogs for miniature gears I find listings for 32 pitch, 28 pitch etc. I am pretty sure I know what pitch diameter is but what is gear pitch? I know it has nothing to do with the diameter of the gear because there are several diameter of gears with the same pitch. Is that the same as teeth per inch? I don't find it defined in the engineering data at the front of the catalog.

  2. #2
    Bill's Machine Shop is offline Hot Rolled
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    It has to do with the size of the tooth. Others will chime in and give you way more than you will ever need to know. WWQ

  3. #3
    Finegrain is online now Titanium
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    Pitch is the distance between teeth. There is diametral pitch for English, and metric module pitch for metric. Now the teeth are arranged on a circle so that the tips are farther apart than the roots so you have to clarify where on the tooth you're measuring. Typically we say that the pitch circle is where the pitch is measured. The pitch circle is about halfway between the tips and the roots. For diametral pitch, the # means how many teeth will fit on a pitch circle of 1" diameter. For metric module, it is the arc distance x Pi along the pitch circle from one tooth to the next.

    So, a 16DP gear with 32 teeth has a pitch circle of exactly 2" diameter. If you "straightened out" the gear, the teeth would be 1/16" x Pi apart.

    A 2mm metric module gear with 32 teeth has a pitch circle of exactly 64mm diameter. If you straightened this gear out, the teeth would be 2mm x Pi apart.

    There are a gazillion other parameters and formulas for the rest of the gear form.

    Regards.

    Finegrain

  4. #4
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    Wink Depends on which pitch you mean

    The diametral pitch (abbreviated P or d.p.) is the ratio of the total number of teeth on the gear to the pitch diameter, expressed as teeth per inch. If you have gears with a diametral pitch of 12, a 12-tooth gear will have a pitch diameter of 1", while a 24-tooth gear will have a p.d. of 2".

    The circular pitch (p) is the distance along the pitch diameter from the face of one tooth to the corresponding face of an adjacent tooth.

    - Leigh

    Ref: Boston Gear catalog, Engineering Information section, page 134.
    Last edited by The real Leigh; 02-03-2010 at 04:43 PM.

  5. #5
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    johnoder is online now Diamond
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    In Imperial jargon, it is Diametral Pitch, which equates to how many teeth can be put on a gear with a 1.0000" pitch diameter.

    A little different in the metric world, where it is simply Module and equates to again how may teeth can fit on what pitch diameter, but in a different way.

    I.E., if I can get 20 teeth on a 40mm pitch diameter, the tooth size is said to be 2 Module. If I can only get five teeth on that same 40mm P.D., it is 8 Module

    John Oder

  6. #6
    5thwheel is offline Stainless
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    Now it is coming back to me. It has been nearly forty years since I needed to deal with that. Thanks for the lessons. I went on the internet but only found formulas which are also helpful.

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