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Thread: Diametral Pitch Question

  1. #1
    Associate Engineer
    Join Date
    May 2016
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    1

    Diametral Pitch Question

    Hi,

    I am new and stumbled upon this forum while trying to find an answer to my gear question.

    I am trying to determine the diametral pitch of 2 gears for which I know the tooth count and center to center width.

    The 1st gear needs to be 34 teeth and the 2nd gear 28 teeth, while achieving as close as I can to a 2-1/8" center to center distance.

    Before I can order these gears I need to know the correct diametral pitch that gets me as close as I can to the 2-1/8" center to center distance.

  2. #2
    Technical Fellow jboggs's Avatar
    Join Date
    Mar 2011
    Location
    Myrtle Beach, SC
    Posts
    788
    I have no idea what your final answer will be but you have all you need to figure it out. You know the tooth counts, which means you know the gear ratio, which means you know the pitch diameter ratio. The center distance is the sum of the pitch radii. You don't know what the pitch radii are, but you know their sum and you know their ratio. So you have all you need to figure it out.

  3. #3
    Principle Engineer
    Join Date
    May 2015
    Posts
    163
    34/28 = 1.21428…

    R1 + R2 = 2.125

    R2 = 34 R1 / 28 = 1.21428 R1

    2.2148 R1 = 2.125

    R1 = 2.125 /2.2148 = .95968”

    D1 = 2R1 = 2*.95968 = 1.91935”

    The diametral pitch would be 28/1.91935 = 14.588”

    This is a non-standard pitch.

    Standard 14 DP gears have a bit larger center to center distance:


    Small gear radius = 1 inch and large gear radius = 34/28” or 1.21428 for a center distance of 2.2148”

    16 DP gears have a smaller center to center distance:

    Small gear P.D. = 28/16 = 1.75” and large gear P.D. = 34/16 = 2.125”

    Half the sum of the P.D.s is the center distance or (1.75 +2.125)/2 = 1.9375”

    If you need something closer you are in the market for custom made gears (perhaps helical).

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