Hello from Doncaster in the UK

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J

Jans husband

Member
Joined
May 4, 2020
Messages
278
Location
Doncaster England
I am new to the site. Everyone seems to be very friendly and helpful.
I came across the site whilst researching information about taps and dies, because I have been making kit pens for about 4 years, and thought I would venture into the world of witless pens. A lot more involved than I anticipated!!
My main query is what is the formula for the diameter of the tenon when making an external thread with a die-say 12mm x.75. There must be a formula out there somewhere.
I have a chart showing the drill sizes for tap sizes-surely there must be a similar chart for dies, or am I missing something?

Looking forward to being involved with the site!
Mike (Jan's husband
 
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monophoto

monophoto

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Joined
Mar 13, 2010
Messages
2,545
Location
Saratoga Springs, NY
Hi Mike

The threading question should be fairly straightforward - in metric world, an M12-.075 thread has a nominal major diameter (diameter over the peaks of the threads) of 12 mm, and a thread pitch (depth) of 0.75mm. So what that says is that the tenon that you intend to thread at M12-0.75 can't be any smaller than 12mm. Theoretically, you can cut that thread on a tenon that is more than 12mm OD, but the larger the tenon, the harder it will be to cut the thread because you will then have to remove more material to achieve the 12mm major diameter. So I think the simplest answer is that you should aim for a tenon OD that is as close to the major diameter of the final thread as possible, or in the case of an M12-0.75 thread, 12mm.

Metric thread specifications also can include a tolerance specification that determines how loosely the male thread fits into the female thread. As I understand it, the effect of the tolerance is to reduce very slightly the major diameter of the thread.

I've found that having the iEngineer app on my phone makes it fairly easy to look up obscure information on threads.
 
J

Jans husband

Member
Joined
May 4, 2020
Messages
278
Location
Doncaster England
Judging from Louie's reply, it is me that is witless and not the pens!!
I didn't think it was as straight forward as that. Thanks. I will do a few experimental pieces first, before I get cracking on the real thing.

Many thanks for the welcomes.

Keep safe

Mike
 
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