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Inspectors Bolt Gauge for ShtLE

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englishman_ca View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote englishman_ca Quote  Post ReplyReply Direct Link To This Post Posted: April 11 2020 at 3:41pm
Remember, the old non standard engineering specs were a standard at one time, for somebody.

At the time that Enfield was getting into tooling for mass production (circa 1856) and needed standardisation, there was no universal standard of measurement so they stuck a stick in the sand and established their own. 
The Imperial inch standard came later. A difference of 0.0004 inches, I believe. It caused all kinds of initial problems with tolerance stacking for Lithgow.

Some of the strange thread pitches might seem bizzare to some these days. Why a thread pitch of 26-1/3 per inch??  Simple answer actually, the change gears for thread cutting on the lathes just worked out that way and was actually an easy gear change to do on that equipment. Most modern machinery does not have these screw cutting gear ratios and combinations, they have different sized gears. 

The Enfield thread form is a little different in angle and has rounded crests and valleys. But cutting tools can be made, little problem. Enfield thread forms work well and are robust.

So back in 1856 a screw 0.181 inch in diameter and 26-1/3 thread pitch was straight forward to make, where as a modern common Unified threaded screw might have been a challenge with special tooling needed.

One thing that I don't have is a set of Enfield thread taps and dies. If somebody ever had some made, I am sure that they would sell well. 
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pisco View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote pisco Quote  Post ReplyReply Direct Link To This Post Posted: May 12 2020 at 2:24am
a set of taps and dies would be handy
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Zed Quote  Post ReplyReply Direct Link To This Post Posted: May 12 2020 at 11:44am
When I replaced the bolt body for the No1MkIII*. The new bolt body was 0.006" six thousandths of an inch longer than the original when fitted. Measured with the same bolt head. Head space was on the field gauge limit (0.074") with the original bolt and now is around 0.068". However to fit the new bolt, it required very careful stoning on one lug to get equal contact on both. I used jeweller's Arkansas stone to adjust the lug. Probably only 1 or 2 thou removed to get the fit.
If you want to use the new bolt as a test; test the lug contact when you check the headspace. You may need a few thou' of that head space to get the lug fit adjusted.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Shamu Quote  Post ReplyReply Direct Link To This Post Posted: May 12 2020 at 1:27pm
Weren't most of them BA?
Check out Brit old car collectors sites they used BA a lot IIRC. MG comes to mind
specifically.
These guys in Oz?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote The Armourer Quote  Post ReplyReply Direct Link To This Post Posted: May 12 2020 at 2:40pm
Originally posted by Shamu Shamu wrote:

Weren't most of them BA?
Check out Brit old car collectors sites they used BA a lot IIRC. MG comes to mind
specifically.
These guys in Oz?



The number 4 rifles were (primarily) BA threads but the No1 MK3 were weird Enfield inch 'specials'

Example - Ejector screw on the No4 is 3BA, whilst on the No1 Mk3 it is 0.1656" x 37 TPI
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