Hello,
A friend asked me about the exact thread size of the French 24 mm fuze thread (24-31 fuzes) and it wasn't easy to find official info but a few things I found and wondered why all have different angles:
22-31 thread angle: 44° 40'
24-31 thread angle: 53° 8'
30-38 thread angle: 48° 16'
As you know BSW threads have a 55° angle independent of the pitch and diameter and unified threads as well as DIN/ISO metric threads have 60° angle. So why the different angles on French artillery threads? After some calculations using the Pythagorean theorem and trigonometric functions the answer is simple:
For the French artillery threads only the major and minor diameters were determinated so the angle calculates from these two values. For the 24-31 thread they used smooth values:
Values for the inner thread in the shell:
Major diameter 24 mm, and minor diameter 20 mm, thread pitch 2 mm. So we have a right triangle with 1mm/2mm sides.
Values for the fuze are little different, it had a major diameter of only 23,5 mm. So it has a (wanted) very loose fit in the shell's thread.
For calculations see attached files.
And sorry for boring math - I forgot most of it since my school time :tinysmile_hmm_t: But it was a mystery for me since a longer time why the fuze threads were so different. Especially for the 22-31 mm thread there is no need for a calculation as it can be seen clearly that it is extremely pointed with it's small 44° angle. I always thought the different angles had to do with sealing or resistance against forces but it's simply because of using smooth diameters. And btw: For Prussian artillery threads the same applies but the chosen diameters were not that smooth as for the French threads.
Can one of the French members translate the word "lumiére"? Is it something like fuze hole? The translators don't give plausible results.
A friend asked me about the exact thread size of the French 24 mm fuze thread (24-31 fuzes) and it wasn't easy to find official info but a few things I found and wondered why all have different angles:
22-31 thread angle: 44° 40'
24-31 thread angle: 53° 8'
30-38 thread angle: 48° 16'
As you know BSW threads have a 55° angle independent of the pitch and diameter and unified threads as well as DIN/ISO metric threads have 60° angle. So why the different angles on French artillery threads? After some calculations using the Pythagorean theorem and trigonometric functions the answer is simple:
For the French artillery threads only the major and minor diameters were determinated so the angle calculates from these two values. For the 24-31 thread they used smooth values:
Values for the inner thread in the shell:
Major diameter 24 mm, and minor diameter 20 mm, thread pitch 2 mm. So we have a right triangle with 1mm/2mm sides.
Values for the fuze are little different, it had a major diameter of only 23,5 mm. So it has a (wanted) very loose fit in the shell's thread.
For calculations see attached files.
And sorry for boring math - I forgot most of it since my school time :tinysmile_hmm_t: But it was a mystery for me since a longer time why the fuze threads were so different. Especially for the 22-31 mm thread there is no need for a calculation as it can be seen clearly that it is extremely pointed with it's small 44° angle. I always thought the different angles had to do with sealing or resistance against forces but it's simply because of using smooth diameters. And btw: For Prussian artillery threads the same applies but the chosen diameters were not that smooth as for the French threads.
Can one of the French members translate the word "lumiére"? Is it something like fuze hole? The translators don't give plausible results.
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