--- In Volker Widmann <>
wrote:
>
> Hi Walter,
>
> I could not find out anything about the wentworth
> thread. Could you be so kind as to tell us what it is.
> I'm sure it is a big laugh. :-))
Sorry, I shorted out on spelling, try Whitworth. It's biggest problem
is it uses 55degree thread pitch whereas both the UNF & UNC that was
the standard in the US, Canada (and Britain) and the ISO metric are
60degree pitch. That means that all the carbide threading inserts,
which are 60 degree, cannot cut this thread. Even if you got the TPI
correct. You are much more limited in cutting tools for the thread.
Though you can grind your own lathe tools to match from HSS. And, it's
nearly impossible to find new fasteners in this thread system.
The British did sign on for the UNF & UNC system in 1949 as the
standard, but continued to use the Whitworth based system until they
went metric. This was most troubling in working on any British
produced autos and such like. I still have rethreading tools for
working with this stuff, but it's really hard to find. And
occasionally you still find it on new stuff.
There are quite a few thread standards you can trip over, here's some
links for more reading:
http://en.wikipedia.org/wiki/British_Standard_Whitworth
http://en.wikipedia.org/wiki/Unified_Thread_Standard
http://www.gewinde-normen.de/en/index.html
For instance I use UNF standard 1-72 thread screws in the mod SASS to
hold the support tube. And UNC standard 10-24 screws to hold the
backplate on. In metric, even coarse, these would be much finer
threads and more of a problem as they go into plastic. I would prefer
to use UNC 1-64 thread screws instead of the 1-72, but have not found
a supplier for the screws in stainless.
I've never found what standard the 5/8 - 27TPI thread of audio mic
supports came from. (like is on the tripod mount clamp from Crown for
the SASS) There is also a 7/8 - 27TPI thread associated with
audio. These sizes are hard to cut on a lathe as most lathes have no
27TPI feed, I can't cut them on my lathe without a custom lead screw
which would be very expensive. Taps and Dies in these sizes are
special order items and expensive. I managed to get two of each of the
sizes taps and dies a few years ago. I'm very careful when I use them.
It gets a whole lot less amusing when you have to deal with this sort
of changing standards. My tools are dual sets of metric and the
Unified standard. Costs double to be equipped but I can handle and
machine both. Here, as in England, metric is the newcomer. Just
recognizing and using the correct thread can be a problem. My tractor
and it's implements contains fasteners, pins and connectors that are
metric and non metric. And the tractor, though it says Ford and New
Holland on it was made by Mazda in Japan. And is definitely not all
metric. Same with all my cars, a mixture of standards. And we have not
even gotten into all the variations of head designs.
Walt
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