Cylinder drain cock thread?

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.

Howard

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?

Bill

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.

John

Thanks, John, I'll take a look.

Bill

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.