No. 4 Help

[Calif-Steve]

Guys I hope somebody can help. I have been working on a No. 4 and want to get it right. I have found the rear trigger guard screw is stripped. I can hardly see any threads and don't know what to do. Is there slightly larger self-tapping Army issue screw? What did the British do in this matter? Thanks guys.

Information

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[Peter Laidler]

Can I assume that it is the thread in the BODY that's stripped? If so, then in our life, that's the end of the line I'm afraid. But it'd be a poor craftsman who couldn't fix it. If it were me I would drill out the stripped thread and silver solder in place a steel insert. Then set the body up on a drilling/milling table and re-drill and tap to the usual 94BA or whatever it is. I suppose you could get a good tig welder to fill the hole in and drill and tap.........

[browningautorifle]

I suppose you could get a good tig welder to fill the hole in and drill and tap.........

In our case, that would work and probably be the way to go. Now about that tap...

[Patrick Chadwick]

Can I assume that it is the thread in the BODY that's stripped? If so, then in our life, that's the end of the line I'm afraid. But it'd be a poor craftsman who couldn't fix it. If it were me I would drill out the stripped thread and silver solder in place a steel insert. Then set the body up on a drilling/milling table and re-drill and tap to the usual 94BA or whatever it is. I suppose you could get a good tig welder to fill the hole in and drill and tap.........

Well I have BA equipment down to 16BA, and some sub-mm wtachmakers tooling, but 94 BA could be tricky. So as poor weather stopped gardening, I attempted to work out what 94 BA would be. You need to know that pitch of 0BA is 1 mm and the pitch of each higher numbered thread is obtained by multiplying the pitch of the lower number by 0.9 so K-BA has a pitch of ${\displaystyle p=0.9^{K}}$ rounded to two significant figures in mm. The major diameter is given by ${\displaystyle 6p^{1.2}}$ rounded to two significant figures in mm and the hex head size (across the flats) is 1.75 times the major diameter.

94 BA works out to a pitch of about 50 nanometers.

No wonder I can't see any in the spares box!

[Maxwell Smart]

Or shock, horror you could go all agricultural and put a longer bolt through it and put a nut on the end.

[Peter Laidler]

Ah, the 4BA tap....... Calif Steve has been a good forumer for many years so I'd just send him a set to do the job.........

[Calif-Steve]

Peter, the 4BA tap. Any chance I can purchase one locally? In my summers I go up to Summer School at Lassen Community College. They have a full-time Gunsmith School. Lots of fun. I can get it welded there (Tig weld??) and tap it there. Thank you gentlemen.

[browningautorifle]

They have a full-time Gunsmith School.

They might have it you know...just possible.

[breakeyp]

British taps and dies can often be found at motorcycle parts stores.

[henry r]

The smaller BA taps can be found at model railway shops, I'm not sure if they normally go up to 4BA. If not there are plenty for sale on the internet.