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Thread: Change gear ID?

  1. #1
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    Default Change gear ID?

    I bought my Boxford lathe from a guy who bought it at an auction and some of the change gears don't appear to be for a Boxford. Its ok as Boxford gears seem to be pretty common and the majority are correct.

    These three are clearly much bigger though with a width of about 0.625 inches and bore of 0.80 inches. Anyone have a clue as to what they fit?



  2. #2
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    0.625" is 15.875mm - say 16mm

    0.80" = 20.32mm - say 20mm

    The gears could be metric - MOD1 - where the OD of the 55 tooth centre gear would be 55 + 2 = 57mm

    If that is the case, the pressure angle would probably be 20 degrees

    For an "inch" gear the pitch circle diameter is Number of teeth/Pitch Diameter and as 55mm = 2.165" assume 2" in which case DP = 55/2= 27.5

    I'd have expected a whole number for the DP but "1/2 numbers" are in use as well.

    Its a wild-ar$ed guess but at least its a start.

    Having the OD would help.

    Last edited by oldtiffie; 07-01-2012 at 10:21 PM.

  3. #3
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    Thank you for the guess. The OD of the 55 tooth is 91.80mm/3.615". The 64 tooth in just over 4"/102.85mm. The 56 tooth is almost the same size as the 55 tooth gear. What ever machine they came off of, these gears are big!

  4. #4
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    Thanks for the extra info - appreciated.

    I was way out.

    For the 64 tooth gear where as a first guess the PCD is 4 ":

    DP = 64/4 = 16

    OD = (no. teeth + 2)/Pitch circle diam (PCD) = 4.125"

    As the gear theOP has has a diameter of 4.05" (102.85mm) and the difference is 4.125 - 4.05 = 0.075" I'd pretty much settle for the gear being 16DP.

    I will check again for metric later.
    Last edited by oldtiffie; 07-01-2012 at 11:01 PM.

  5. #5
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    Thank you for the help! I think the gears are 16 dp as they all seem to average very close to that. I remeasured the bore, it is closest to 13/16" but it will be a snug fit.

  6. #6
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    I re-did the 64 tooth gear in metric and assumed the pitch circle diameter to be 100mm and the gear to be MOD 1.5

    But PCD = 64 x 1.5 = 96 and OD = 96 + (2 x 1.50) = 96 + 3 = 96mm

    That is too far below the actual PCD of 102.85mm - so disregard modular gearing.

    I would just about bet that the pressure angle is 20 degrees.

  7. #7
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    I re-did the calculations again as I made an error as regards the addendum - it is fixed now.

    For the 64 tooth gear where as a first guess the PCD is 4 ":

    DP = 64/4 = 16

    Addendum = 1/DP = 1/64

    OD = PCD + (2 x addendum) = 4 + (2 x 1/64) = 4 + 2/64 = 4.031"

    As the gear the OP has has a diameter of 4.05" (102.85mm) and the difference is 4.05 - 4.03 = 0.02" I'd pretty much settle for the gear being 16DP.

  8. #8
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    OK thank you for the help.

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