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Old Jan 20, 2010, 08:05 AM
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
Old Jan 20, 2010, 08:57 AM
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
Old Jan 20, 2010, 07:41 PM
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 <char...@gateho.gotadsl.co.uk>
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
Old Jan 21, 2010, 03:40 AM
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
Old Feb 09, 2010, 04:58 PM
dave sanderson
Guest
n/a Posts
Re: Minor Diameter calculation

On 20 Jan, 14:05, John <harriscam...@hotmail.com> 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
 


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