Jan 20, 2010, 08:05 AM John John Guest n/a Posts Minor Diameter calculation Many years ago my father used an equation to find the minor diameter of a thread. Unfortunately I have forgotten it and my father is no longer around to ask. I have looked at various equations, calculation programs and tabulated information on the internet and they all seem to produce different answers. Does anybody know an equation which from experience will produce reasonably accurate result when calculating the minor diameter of a thread? Thanks. John H
 Jan 20, 2010, 08:57 AM Charles Lamont Charles Lamont Guest n/a Posts Re: Minor Diameter calculation John wrote: > Many years ago my father used an equation to find the minor diameter > of a thread. Unfortunately I have forgotten it and my father is no > longer around to ask. > > I have looked at various equations, calculation programs and tabulated > information on the internet and they all seem to produce different > answers. > > Does anybody know an equation which from experience will produce > reasonably accurate result when calculating the minor diameter of a > thread? There is no universal equation. There is a formula for BA threads only, because they are almost unique in being a mathematically derived series. In general, you need to know the size and thread designation, and if not a standard thread, the thread form and pitch. Thread form and pitch will enable you to find the theoretical thread depth, and that gives you the minor diameter. -- Charles Lamont
 Jan 20, 2010, 07:41 PM mecc_smith mecc_smith Guest n/a Posts Re: Minor Diameter calculation If the threads are very old they may be Whitworth which was also formula driven. On Jan 20, 11:57 am, Charles Lamont wrote: > John wrote: > > Many years ago my father used an equation to find the minor diameter > > of a thread. Unfortunately I have forgotten it and my father is no > > longer around to ask. > > > I have looked at various equations, calculation programs and tabulated > > information on the internet and they all seem to produce different > > answers. > > > Does anybody know an equation which from experience will produce > > reasonably accurate result when calculating the minor diameter of a > > thread? > > There is no universal equation. > > There is a formula for BA threads only, because they are almost unique > in being a mathematically derived series. > > In general, you need to know the size and thread designation, and if not > a standard thread, the thread form and pitch. Thread form and pitch will > enable you to find the theoretical thread depth, and that gives you the > minor diameter. > > -- > Charles Lamont
 Jan 21, 2010, 03:40 AM Charles Lamont Charles Lamont Guest n/a Posts Re: Minor Diameter calculation mecc_smith wrote: > If the threads are very old they may be Whitworth which was also > formula driven. The relationship of pitch to diameter in Whitworth threads was determined empirically and does not follow a formula. -- Charles Lamont
 Feb 09, 2010, 04:58 PM dave sanderson dave sanderson Guest n/a Posts Re: Minor Diameter calculation On 20 Jan, 14:05, John wrote: > Many years ago my father used an equation to find the minor diameter > of a thread. Unfortunately I have forgotten it and my father is no > longer around to ask. > > I have looked at various equations, calculation programs and tabulated > information on the internet and they all seem to produce different > answers. > > Does anybody know an equation which from experience will produce > reasonably accurate result when calculating the minor diameter of a > thread? > > Thanks. > > John H for metric threads taking pitch from the designation gives a pretty good approximation, at least for tapping drills. E.g. M6x1 -> tapping drill 5mm Dave