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Cylinder drain cock thread?

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Howard Lewis09/07/2021 18:55:26
6032 forum posts
14 photos

If it is Whitworh form thread, you should be able to extend the profile and measure it as 55 degrees.

The pitch can be measured directly off the scan or shadowgraph.


John P09/07/2021 19:58:43
404 forum posts
256 photos

Posted by Bill Davies 2 09/07/2021 15:12:46

Mike now has many options for reproducing the thread; does anyone have a
design for a shadowgraph type projector?


Not really a shadowgraph but a cheap alternative.
Was in MEW 189 to 191 in 2012.
A ground screw cutting toolbit comparison with a 55 deg
12 Tpi Whitworth thread gauge.


Bill Davies 209/07/2021 23:55:36
278 forum posts
11 photos

Thanks, John, I'll take a look.


Mike Hurley10/07/2021 20:11:53
305 forum posts
87 photos

Interesting reading the article on the 'poor mans shadowgraph' in the MEW back issues. Just a bit time consuming for me to tackle at present as its just really an odd one-off job , but many thanks for the suggestion John.

I'm trying a few more versions of some of the earlier suggestions (wax, plastics etc) to try and get a sharper profile, and possibly try a scanner as suggested if I can get a reasonable 'moulding'. They are quite old & not exactly pristine threads, so not too hopeful of the outcome but can only try ones best. I then need to determine the angle of taper (ready to cut new 'plugs' / stopcocks or whatever ends up going in them 'oles!) as I'm not assuming that's going to be any standard either, but will be easy enough to do.

Thanks again for all the feedback guys.

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