A note about thread direction in Hotchkiss Fuzes

[Birdseye]

It is prety standard (universal?) that base fuses screw in with a reverse thread. This is done, ostensibly, so that the twist imparted on the shell by the rifleing further tightens it rather than, embaressingly, unscrewing it in flight and causing it to fall at the enemy's feet.

One would think, therefore, that all the threaded bits of a base fuse would follow the same design logic.

Right?

Well, imagine my chagrin when, while attempting to remove the percussion charge retaining screw on a Hotchkiss 1900 fuse, I found that the clockwise rotation served to further tighten it!!!!

I have another Hotchkiss fuse body, recently purchased, which shows that the fireing pin retainer is also threaded conventionally. That is to say that, for Hotchkiss base fuses at least, only the body is reverse threaded.

I suspect that this might explain some fuses that are "difficult" to take apart.:tinysmile_fatgrin_t

 

[HAZORD]

That's a good observation! I would add that a number of Jap nose fuzes are left hand thread. It always help to try both directions.

 

[Chris 42 RQ]

Left or Right hand ?

Do not forget that not ALL guns are right hand rifled !

Although it would be dangerous to use right hand fuzed ordnance in a left hand weapon for the reasons you describe.
:afraid:

 

[Birdseye]

Do not forget that not ALL guns are right hand rifled !

Although it would be dangerous to use right hand fuzed ordnance in a left hand weapon for the reasons you describe.
:afraid:

Actually what I am saying is that some part of the Hotchkiss base fuses that I examined would, theoretically, unscrew regardless of the direction of the rifling.

 

[2pounder]

threads

I suspect that there might be enough force due to the fuzes inertia pushing rearward as the shell accelerates and direction of rotation to undo a fuze if not thread handed to make sure it tightened up. However the front part of a base fuze also has a force pushing it rearward and if the thread by hand direction were to make it unscrew this would be against the rearward force so cancel each other. I know what I mean but not sure I've explained it well enough. Also once a shell leaves the barrel it slows down in forward velocity and rotation (often used to arm fuzes and make them bore safe) so thread direction becomes irrelevant due to the low forcese involved being unable to overcome punching and indenting.

Thats my theory, does it sound ok??
2pr

 

[Birdseye]

I suspect that there might be enough force due to the fuzes inertia pushing rearward as the shell accelerates and direction of rotation to undo a fuze if not thread handed to make sure it tightened up. However the front part of a base fuze also has a force pushing it rearward and if the thread by hand direction were to make it unscrew this would be against the rearward force so cancel each other. I know what I mean but not sure I've explained it well enough. Also once a shell leaves the barrel it slows down in forward velocity and rotation (often used to arm fuzes and make them bore safe) so thread direction becomes irrelevant due to the low forcese involved being unable to overcome punching and indenting.

Thats my theory, does it sound ok??
2pr

err ... the rearward force acts equally on all the components of a fuse so that all threads would be more or less "locked".

I have no answer or even conjecture as to why some pieces are one way and others the other.

 

[HAZORD]

The whole tightening and unscrewing dynamic is an interesting observation. I have seen a number of 155mm flare projectiles, where the nose fuze has partially unscrewed as the projectile rotation has been slowed by friction with the earth, but the fuze wanted to stay at the same rpm, and unscrewed itself a few turns.

 

[Birdseye]

Makes me wonder if there is a bit of urban legend involved. I mean, it sounds plausable that a fuse would spin out, no?

Come to think of it, I only recall reading words to the effect "the base fuse is reverse threaded to further tighten it during flight". I have never read "the base fuse is reverse threaded to prevent a reoccurred of the unfortunate incident where 10 miles of German Howitzers shot duds for 3 days".

Hmmmmm ....

 

[2pounder]

fuze threads

Cant find anything in my books as to why LH threads on base fuzes but it is still common practice. Can Mr Fuze confirm that most countries carry out this practice and can someone else maybe confirm all guns have rifling to give clockwise rotation from the shell base?
I cant believe the fact is not based on practical knowledge. As to threads undoing due to rearward pressure it is alleged that this was found to occur on large naval guns firing reduced charges having their breaches undo.

 

[Chris 42 RQ]

LH or RH ?

Sadly I no longer have access to the information neeeded here, but believe from memory that a few early Soviet guns had left hand twist rifling and they were not alone !

Having said that I have yet to see any fired projectiles on this site that "do" have left hand rifling ?:banghead:

 

[SG500]

Sadly I no longer have access to the information neeeded here, but believe from memory that a few early Soviet guns had left hand twist rifling and they were not alone !

Having said that I have yet to see any fired projectiles on this site that "do" have left hand rifling ?:banghead:

Chris, here's one, you may recognise it!!!!!!!!!

Dave.

 

[Chris 42 RQ]

Affirmative.

Yes Dave I do recognise it !:elefant:

It may be in Wet Welsh Wales but it did go to a good home !