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  1. #11
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    First of all I want to explain some basics about the construction of many ammunition parts. The shape of most projectiles and fuzes is consisting of the following elements which are: flat, cylindrical, tapered and radii. The cap which is needed has three of these elements: the bottom part is flat, the sides are tapered and the front has inner and outer radii. This combination makes it a very complicated part in conventional turning because a normal lathe can turn flat, cylindrical and tapered parts but not a radius.

    What I found was the following drawing (A) with some basic measurements of the cap. But after some further examination these few measurements are all what's needed to make this cap. So I made a computer drawing of the cap (B) and put it as a layer over the original drawing (C). There was some small difficulty because the inner diameter obviously had a typo. Instead of 35,5 mm (which is larger than the thread diameter) I think 33,5 mm is the correct measurement instead. To show the shape of the radii I put some circles into drawing (B).

    Taking into account that the drawing was made in 1886 using primitive techniques, the paper of the document was wavy and the picture was taken with a camera, it is pretty impressing how accurate it is:
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    Last edited by Alpini; 2nd March 2021 at 01:48 AM.

  2. #12
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    Now after all measurements being clear I started to make the templates. As I have a old engraving machine (pantograph) I decided to make larger templates from aluminium sheet metal in 1:5 oversize and milling it into 3 mm steel 5:1 scaled down. Through this procedure also failures in machining the aluminium template are scaled down 5:1. To make the aluminium template I used just tin shears, a ruler a circle and a file and it was done within 10 minutes.

    The first try of milling the steel template was a fail. When copying 1:1 with a pantograph the diameter of the endmill must be the same like the probe tip so I used a 5 mm endmill and a 5 mm probe tip. But when copying 5:1 the probe tip diameter must be multiplicated by 5 so 25 mm was the correct diameter :-). After this milling the 1:1 size steel template was easy. In the last picture I did a optical check if the size of the template fits to the size of the primer screw.
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  3. #13
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    the next three pictures show:

    -the setup of the template for the inner shape with the turning tool mounted upside down on the lathe tracer attachment (picture was taken after finishing the first cap so it's not in the right order)
    -after turning the inner shape
    -test fitting the primer screw after screw cutting (this time done with the lathe without thread tap)
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    Last edited by Alpini; 2nd March 2021 at 12:23 AM.

  4. #14
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    the next four pictures show:

    -cutting of the workpiece
    -screwcutting a outside thread on the remaining metal bar as workpiece holder for the last machining step.
    -workpiece turned by 180° and screwed on the new workpiece holder
    -the finished cap after turning the outside whit the help of the second template
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  5. #15
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    The last pictures are showing the finished primer screw, the complete fuze and the three tools made for this small project.
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  6. The Following 10 Users Say Thank You to Alpini For This Useful Post:

    Andysarmoury (2nd March 2021), Bever (2nd March 2021), greif (2nd March 2021), M8owner (2nd March 2021), nachtwuenscher (2nd March 2021), Snufkin (2nd March 2021), TimG (2nd March 2021), tnor_fr (4th March 2021), ulaire (4th March 2021), wichitaslumlord (3rd March 2021)

  7. #16
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    Another great job Stefan.
    Richard

 

 
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