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Restoration / Repair of a Dopp. Z. 08

Alpini

Well-Known Member
Premium Member
Hello,

in this tread I'll show a longer report of the restoration / repair of a Dopp. Z. 08 which is going a little bit beyond cleaning and painting it with some color. My main goal of the project was to get the fuze's mechanics/clockwork fully operational after 110 years. The only exception - of course - is the detonator as it would be a violation against our laws.

The Dopp. Z. 08 (Doppelzünder 1908) was the worlds first mechanical time fuze which was working well and suitable for mass production. It still had some minor problems but it's main problem seems to be that is was ahead of its time. Because of this it was declared obsolete not long after it's introduction. Basically this fuze was invented for the shrapnel shells of long range guns because powder train time fuzes with slow burning powder for such Long distances prooved very inaccurate.The fuze shown here is a separate type which was used on parachute illumination bombs, dropped from the Zeppelin's. The main difference between the artillery and bomb Dopp.Z.08 is that the artillery 08 was activated by the inertial force during firing. The bomb 08 was activated by a pulling cord.

The fuze and it's clockwork was invented by Krupp. The later Dopp. Z. 16 with the improved clockwork has it's roots in the Dopp.Z.08. After 1st WW this improved clockwork (System Krupp-Thiel) was used by many countries and I guess it's in service in some countries still today.

First of all I'll show two photos of the condition how I got the fuze an a drawing of the fuze. The red marked parts in the drawing were completely missing and I had to make reproductions of them because there is nearly zero chance to find such spare parts. The blue parts were damaged. Some of the blue parts I could replace with parts from a different Krupp clockwork and one part needed to be reproduced too.

I know my english is not the best so please let me know if something is impossible to understand. Especially correctly naming the small parts is nearly impossible for me.

Many thanks to @BurneyDavis for helping me.
 

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So let's start with the reproduction of part No.1. Which was one of the very difficult parts and it was the first project which I had to make a punch die for.

The first steps consisted of manually cutting a sheet metal disc and giving it a center hole:

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In the next step I was turing the disc into cup shape with the help of the very old "metal spinning" technique. Heating the sheet metal first is helping to make the cold forming a little bit easier. After metal spinning I was just trimming the work piece to correct length.

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Now it was time to build a punch tool. It took me a whole Saturday to finish a prototype set of tools. I don't want to bore you with to many fotos of the production of them so I start with pictures of using the "special tools":

The first picture shows the punch die:
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The second picture shows the apparatus assembled and ready to be placed into a hydraulic press. "M8owner's" press would be perfect for this work. But I don't have such a press so I used my largest vice which could be improoved. I had the feeling the vice was near to break into pieces :)
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The next picture is showing the result: the first prototype :)

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In the last picture I tried if my reproduced part will fit into the original small brass part and it did perfectly.

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To be continued...
 

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thank you :) But it would be impossible without good machines and tools ;-)

Next I needed a depression in the nearly finished prototype. This was compared a very easy task because I could use the same "chuck" / "guide" which I made for the punch operation again, just with different insets:

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Now only the very small (7x4mm) part No. 5 was missing to finish this part (I was very wrong here but I'll tell later :) )

For this small part I made a 1:10 scaled drawing which I printed out. Then I could put this drawing on my engraving machine and adjusted the pantograph to the opposite 10:1 scale and engraved just very flat the shape into a rusty piece of sheet metal. The remaining work was just drilling two 1 mm holes and 20 min of annoying filing:

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That's a serious amount of work! Well done,look forward to seeing the next part of the restoration. Tig.
 
more pictures:

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some time later (to late in the evening) I drilled the two holes to fix the small part into the wrong side. This was the first time I could start crying :) Later I closed the wrong holes with two welding spots and made them invisible. So my first prototype was finished:

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Some time later I again looked at Burney Davis' photo of the clockwork and got a bad feeling about the steel sheet metal I used and asked him about the right material. It wasn't what I wanted to hear but he said "it's very thin Aluminium", damn :)

So in conclusion my prototype had several failures:

-steel instead Aluminium
-the impression in the center had the wrong angle/diameter
-the small part No. 5 was made from to thick metal
-the rivets holding part No. 5 were made from steel but originally from brass
-the 4 segments were missing some very small "flaps" (I found them to complicated to machine into the dies the first time)

I still was motivated enough so converted the dies to have the small flaps present and made a new part from Aluminium without the other former failures:

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Fixing the rivets was a challenge, these have a size of 1.00 x 1.40 mm and they are not easy to handle. I turned the rivets on the lathe from 2 mm brass welding wire. The first few of them all fell down somewhere in my workshop (I did never seen them again :) )

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Now I was happy with the result - one complicated step finished - more following...
 

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The next problems which I had to solve were 2 broken brass gears of the clockwork (both were missing some teeth) and one broken very small steel pinion with one missing tooth. I don't have an idea how all the teeth could break. Maybe someone was playing with the clockwork after war which caused the damage.

The following picture shows all broken parts:

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Because I had some spare relic Dopp.Z.08 clockworks (most of them totally broken) I could replace the parts 6 & 8 with parts from my spare clockworks. Part No. 8 I had to replace three times because my new gears also broke during assembly on the pinion. I didn't take pictures of this work.
 

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Part No.7 was the main problem. For some weeks I had no idea about how to solve it. Looking for normal watch parts which may fit did fail. A watchmaker gave me an answer like:

"Most of us sell watches and we are able to change batteries in quartz clocks or fix a new bracelet. If you really should find a watchmaker who can machine a new pinion you don't want to pay the price for his work" :)

So I decided to find out which module size the pinion has. It was not easy because in such a small size (the pinion is diameter 3.22 mm) a small meassuring failure lead into a very wrong module size. After some time I found out that I can prove my calculated module size by using a formula wich is calculating the module size with the help of the distance between the two axis and the number of teeth of the gear and pinion. So I was able to caluclate and prove a gear size of m0.286 which was a standard size at this time.

Now as I knew the module size I decided to try milling a new pinion myself. I estimated my chance to machine a running pinion is very small because I don't have a 5 kg watchmakers lathe but a 450 kg toolmakers lathe (same for the milling machine). In eBay I found a gear milling cutter in nearly the right size (m0.273) which I decided to buy. The right size gear milling cutter wasn't available anywhere on the world. Todays module sizes are standardized much different than 110 years ago.

When I received to milling cutter I thought the package was empty. The cutter had a diameter of 10 mm. The eBay picture was a good macro photo which led me think its about 30 mm in size.

Ok - now I made a quick & dirty milling arbor for the gear milling cutter. For size comparsion in the next pictures: The clamping screw is size M3 (for the american readers: it's about the size of a #4-40 UNC screw) :bigsmile:

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for the pinion I found a 3.5 mm silver steel shaft which I turned down to the needed diameter of 3.22 mm and gave it centering holes on both sides:

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Now the shaft was ready for the dividing head on the milling machine. The dividing head is as old as the Dopp.Z.08I think but it still works very well. The next picture is just showing meassuring operation to adjust the shaft parallel to the milling axis and to find the center of the shaft:

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Now the actual milling operation for 10 teeth was relatively quickly done:

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Now the work continues again on the lathe to turn the pinion to it's final size:

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I made three of the pinions because the first two were 0,2 mm to long and jammed between the upper and lower plate of the clockwork. The third had the right length so i just needed to rivet the brass gear onto the pinion and it was finished.

Some pictures:

On the left side the original broken pinion, on the right side one of the two to long prototypes (for size comparsion on a one Cent coin):
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The complete assembled pinion with a replacement brass gear:
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to be continued...
 

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Now I thought that I was ready for the final assembly of the clockwork but during assembly one half of the long straight spring of the following part broke:

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The spring meassured ~25 x 0.6 x 0.07 mm and I had absolutely no idea where to get such a part. But then I remembered that the later clockwork (well known from Zt.Z.S/30 fuzes) has a spring like this and I had one damaged S/30 clockwork which contained such a spring (but undamaged). So I carefully disassembled this clockwork and removed the spring. Kindly this spring has exactly the same dimensions like that one in the Dopp.Z.08 clockwork so I could repair this part too. Originally this spring was fixed with a very small 0.3 x 0.5 mm bolt. The new spring I glued in with 2K epoxy glue because I had no idea how to insert such a small bolt.

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now the final assembly of the clockwork was a final assembly:

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The nex small missing part was the "window" of the fuze. Originally it was made of very thin celluloid. This material is not easy to get today. Fortunately a friend had some old celluloid coating removed from old furniture. But this celluloid was red colored and to thick (1 mm). The original celluloid windows sometimes had a slightly red tone and others I have seen on photos were clear.

So I dissolved a small part of the celluloid plate in acetone which then becomes a lacquer and spread it on a glass plate. After 15 min I could remove it from the glass plate with a razor blade (it's like a plastic foil but a litte less flexible).

To cut out a round disc I made a small punching iron on the lathe. This was working well and gave a perfectly round disc. Just the color was to much red in my opinion:

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On the edges of my friend's celluloid plate there were very small areas without the red Color so I made a second try and dissolved these parts (don't have pictures) and produced a clear window.

This better colored windows I glued with hide glue (it's a natural product) into the fuze. Normal glues with solvents cannot be used on thin celluloid. To secure the window I made a small aluminium ring like it was done originally. It is inserted as a press-fit.

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The window inserted into the fuze body:

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to be continued...
 

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A last small work was to turn some missing small screws on my lathe. Because all screws Ave imperial pitches (non-metric) I had no screws available which I could alter so I needed to turn them completely from small steel rods. I don't understand why but the screws had unified threads and as far as I know the unified thread standard was established a long time after 1908.

Turning is a simple task so I did not take any pictures other than from the finished screws:

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As the last step I painted the fuze with shellac which I dissolved in methylated spirits. In factory they were also painted with a special shellac mixture to prevent corrosion.

The result:

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Alpini,
You have the patience of a saint. What a pleasure it has been to follow your restoration. If others had your skills nothing would be impossible. What is your next project ???
Cheers
Hangarman
 
Thank you for your response, nice to hear that the video is working. The timer won't break again. It is designed to survive to be fired from a gun.

Patience is a good word. I had several times during this project were I could start crying :) I don't think such work requires a lot of skills in the form of prestidigitation and I don't have an apprenticeship in metalworking. But it requires a strong intention and the ability of improvisation because I don't have the technical possibilities which the Krupp factory had. I guess they had ~20 machines running to build the parts for which I could use only two machines.

Repairing things is the best way to understand how they work in detail.

Next project is not planned but I did compareable complicated repairs before. But due to the very small size of the parts it was my most complicated project.

My intention is to only rebuild parts of ordnance which are almost impossible to find as originals. I don't like to rebuild complete projectiles or fuzes for example.

Maybe this project is an incentive for other members to try some good restoration projects which they wouldn't have tried without my thread :)
 
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Hi Alpini, I like your restoration very much. Very convincing. Very nic Schellack finish. Before I read your thread I thought that the small window was made from Glas or Glimmer. I touched it and I found it to be quite hard. But Zelluloid is also a good idea for that. I like your spinned and punched out piece very much. The original one is also marked FK like the clockwork. But larger letters and only faint marking. Is FK the only known manufacturer of these clockworks for the 08 ? Do you know what the complete name of the manufacturer is? Best regards, nudel
 
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