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Thread: Help with Pitch Diameter Tolerence!

  1. #1
    Associate Engineer
    Join Date
    Sep 2012
    Posts
    1

    Help with Pitch Diameter Tolerence!

    Iím having a bit of trouble with finding pitch diameter tolerances for odd-ball threads. Iím able to look some common threads up online and in the machineryís handbook, but when I run into something like .4707-32, or #14-24, Iíd like to be able to calculate them on my own.

    Iíve been pretty successful in finding reliable formulas to calculate the basic pitch diameter of any thread, but now Iíd like to be able to calculate the pitch diameter tolerance as well. From ďASME B1.1-2003,Ē the pitch diameter for 2B threads is given as:

    1.3*(0.0015*(BasicMajorDiameter)^(1/3)+0.0015*(LengthOfEngagement)^(1/2)+0.015*(Pitch)^(2/3))

    Iíve been adding what I obtain from that formula to the basic pitch diameter, and comparing the values to this table:

    http://www.threadcheck.com/technical...eters-pg54.pdf

    Iím unclear as to what the ďlength of engagementĒ should be set as. I get closest to this table when I set it to one diameter. When I do this, in some cases, Iím spot on, in many cases, Iím off by one ten thousandth, and in some cases Iím off by as much as a thousandth.

    Can anyone help me?

    This is just for unified threads. I havenít even STARTED looking at metric yetÖ

  2. #2
    Technical Fellow
    Join Date
    Feb 2011
    Posts
    1,043
    Welcome to the forum. I am in no way an expert on threads and thread-tolerances, but my guess for length of engagement relative to a given thread tolerance definition would be a percentage of root diameter.

    Try calculating percentages for a variety of tolerances of a given thread size.

    Failing that, I found about a month's worth of reading with a search on

    thread 6h tolerance

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