Here is some brief information you all have wanted to know about
Whitworth threads. You will be amazed at how interesting a topic this will be
at
your next party. If you need more detail let me know.
It is considered by some that the screw thread was invented in about 400
BC by Archytas of Tarentum (428 BC - 350 BC). Archytas is sometimes called
the founder of mechanics and was a contemporary of Plato.
Early screw threads for fasteners were cut by hand, hindering mass
production Through the years, increasing demands deemed it necessary for them
to
be factory made. In 1770, Jesse Ramsden made the first satisfactory
screw-cutting lathe. J and W Wyatt patented a factory made thread system in
1760
but the lack of thread standardization made fastener interchangeability
impossible.
To overcome these problems Joseph Whitworth collected sample screws from a
large number of British workshops and in 1841 proposed standardization of
the number of threads per inch for various diameters and the angle the
thread flanks at 55 degrees . His proposals became standard practice in
Britain in the 1860's.
Course Whitworth threads called BSW (British Standard Whitworth) from 1/4"
to 1" are the same threads per inch as UNC (Unified Course) except for the
1/2" which is 12 threads per inch for BSW and 13 threads per inch for UNC.
The major difference is that the UNC has 60 degrees between the thread
flanks and a deeper minor diameter. The BSF (British Standard Fine) thread
has the same profile as the BSW thread form but was used when a finer pitch
was required for a given diameter.
Except for the 1/2" thread BSW, threads can be modified with a tap or
chased with a die to fit a UNC nuts and bolts. Due to varying sizes of taps
and dies, try it first to make sure you are satisfied with the fit. The
threads per inch of BSF (British Std. Fine) have no correlation to UNF
(Unified Fine) so they cannot be re-tapped or chased with a die.
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