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10 cm vz.21n length of cap needed

Alpini

Well-Known Member
Premium Member
Hello,

is there anyone who can meassure the exact length of the steel cap of the Czechoslovak 10 cm vz.21n fuze or is there a drawing with dimensions available?

And by the way what does the "n" in the designation mean?
 

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This is a drawing of the 10 cm vz.21n fuze on a 105mm shell with dimensions., and a photograph of an original Czech 10cm vz.21 fuze
fusee-10cm-vz21n-(105).jpg 10cm vz21 czech Screenshot 2023-04-09 164517.jpg
 
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Hi Alpini
I have a company drawing - the production assembly of the vz.21n fuze dated to 1924.

The part you are interested ,,Temeno zapalovače,, in - I have its designation in the Skoda system, but I do not yet know its length.
There is one more option from the documentation, but it won't be right away.
There is also a catalog of Weapons material that also includes components including fuze, springs, etc...

Among other things, the 10 cm Howitzer vz.14/19 had a longer barrel by 5 calibers compared to the vz.14 and the range was increased from 8000 m to 9800 m.
Hence the different timings ..
Akon
 
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@Dreamk: I already know this drawing but it don't has the meassurement I am looking for. And the 10 mm diameter are wrong as these should be 12 mm. But thanks for the additional photo - it shows exactly the cap I am looking for - with two set screws.

Beside the different scales on the time rings I also noticed, that some models have 2 and other models have three set screws on the to cap. Also the fuze thread section is different from the drawing in thread No.#1 - my examples have an additional step above the fuze thread. The area where the safety steel balls are falling outside has a larger diameter and is unthreaded.

@MINENAZ16: Thanks for the link - I thought there was a thread answering the question about the "n" but wasn't really sure. I would be very grateful if you can take that measurement. If the cap does unscrew the length is easy to measure with the depth probing rod of a vernier calliper through the central hole and placing the cap on a flat surface. Sadly on my example the upper part has so much corrosion that it is impossible to reconstruct it's length.

@AKON: I was hoping that you may have original dimensions. But I also know it's sometimes not easy to find drawings with dimensions. For this mostly factory/manufacturing drawings are needed. Normal military drawings usually only have basic dimensions given. Do you know what the small triangles on the time rings mean?

It would be nice to restore this interesting fuze. In my opinion the manufacturing quality of the Czechoslovak fuzes is very high and for 1921 it had a very modern design.
 

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Hi Alpini
I'll try to find the production drawing for the vz.21n fuze - the part "Temeno zapalovače " has the Škoda works marking drawings "Z 309a", (index ,,a,, on the drawing designation means -first change) dated to 1924.
As for the small triangles, I will write to you later when exactly it was used ... and what it meant on ammunition at the time.
Akon
 
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Hi Alpini
I found a numerical data for the design of the top of the vz.21 n floater and it is a drawing of the part under the designation Z-309 (older version) and it reads:
Diameter 52.5mm / 50.85mm / 35mm / 15.3mm / 12mm, length 65mm ,
Thread Type SJ 37x1.5mm.

The form of the entry is almost identical to the original as I am writing it here.
The only thing I added is the word: length and thread.

To the meaning of a small triangle stamped or otherwise made and the embossing washed out with red paint. According to the Decree of the Ministry of National Defense from 1921, this is how a part on a school fuze , which in sharp execution would be filled with explosives or dust... The fuze or ... is ordered to have the inscription "Model ,, (? School-model) and triangles.
Akon
 
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The fuze is maybe uncommon because Vz21n used to be graduated to 240 (+) and Vz21 to 230 (+).
Sometimes we find czech shells in France (used by Germans).
Herewith ground pieces :
VZ21
vz21.jpg


Vz21n
vz21n.jpg



My example of Vz21n (in very good condition) :
vz21 n.jpg
 
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Hello Akon,

thanks a lot for searching. I had to correct the estimated length in my own drawing by -1 mm. My other measured dimensions were nearly correct and differed only by +/- 0,10 mm.

Your mentioned "SJ" thread is interesting. I never heard about it and measured a M37x1,5 :). So I started to search for it. The SJ-Thread is described here as an predecessor of the later standardized metrical threads: https://www.gewinde-normen.de/en/sj-thread.html. The DIN-metrical thread (later with minor changes published as ISO standard) was introduced in 1919 but I think it took several years until it wide spread. Until 1918 all the German and Austro Hungarian fuze threads had an imperial pitch so I think the vz.21 may be one of the first fuzes with metrical 60° thread. Maybe the vz.21 n was then fully DIN-thread compatible?

About the triangles I already guessed that it has to do something with school use. It makes perfectly sense as the fuze was part of a wooden drill round ;-) The striker was blocked with tin metal cast into the fuze.
 
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Hi Alpini, I'm glad that the numerical data helped you.
Regarding the SJ thread, I will try to give you two examples of threads when I have a little more time... .
The first will be from the regulation on taking over k.u.k. artillery ammunition around 1918-1919 with a dimensioned thread profile and the second table will be from Škoda company documentation from the 20s-30s.
The conclusion could be something like this: If you don't have a detailed description of the thread (its profile and especially the tolerance) or the actual counterpart according to which the taper will measure the thread and use it as a replacement caliber during production, the result will not agree. If you have the opportunity to borrow a gauge for threads (eye), then try the Metric thread and you will change your opinion..:)
Then we can discuss it further. I was theoretically dealing with threads on ammo because I used it as one of >50 parameters to design for sorting and then searching the ammo database for actual samples.
Akon
 
Lot No.1 Whitworth to millimeter conversion for military artillery ammunition.
source k.u.k. Artilleriegeschossen , Wien ,1917
Akon

2.jpg
ČSR ammunition threads -1923-1924 ...
Czechoslovak Standardization Society (ČSN) – founded at the end of 1922.
The first use of corporate "standards" was in Škodovka long before that...
The first technical standard issued in the Czech Republic was ČSN 1001:1924 under the name Threads. This technical standard was published in 1924.
Proceedings of the Ministry of National Defense on the use of the index ,,n,, .... from 1924. ( The translation is done by someone more professional than me :)
6.png
7.jpg


Akon
 
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I have a good few of these fuses found metal detecting so they are spent. They do strip down so if you want any other measurements etc let me know.
 
@Bully1970: Thanks, but I think I have all dimensions I need for a good reproduction. The most important dimensions came from @akon. Other dimensions I took from the rusted part I had. To measure the set screw holes I made a primitive section of the cap. The set screws are what we call today M4x0,7 mm which is still in the actual ISO 1502.

Now I am waiting for a T-slot milling cutter required to finish the work...
 

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Hi Alpini
You give this fuze a lot of care and I think deservedly so :)
Unlike those that have a different designation E..D instead of Membr.. so you go under the surface of things and by asking questions I, and not only me, find new kontext :)

Akon
 
It's time to show the final result. I machined it from a 60mm steel bar. After lathe turning and some milling work I phosphatized the parts and finally applied a thin layer of asphalt lacquer and gave it some wear with sand paper. The first picture is a before and after picture.
 

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