Fuze cap reproduction

[Alpini]

Hi,

here's a little restoration thread about a way to produce highly accurate replacement caps for fuzes. In this example I made them for dutch (Vickers) Tijdbuis No.7 (used on HE shells for 7.5 cm Vickers AA guns). I had some fuze bodys and it seems almost impossible to get good condition caps for them (hopefully nobody shouts: "here" now .

I'll show it as an example only because the simple technology could be used for british No.199 fuze caps, german Zt.Z. S/30 etc. too. The original dutch caps for the No.7 were made in two different ways some were made from die cast blanks and others were made from bar material.

Aluminium bar material is quite cheap today and available in all diameters but together with a friend we decided to try casting blanks. But not a real die casting as we don't have a die casting machine. So our caps are less rigid then caps made by die casting and lunkers occured more often.

The first constructions of the mould caused a lot of problems (lunkers) and were improved 4 times until the results were useable. Without feeder heads and risers and enough pre heating the mould the results were unuseable. It isn't good to see but the mould already contains a "core" to form the inner cavity of the caps. The cavity was so nice shaped that no further machining was required. The first moulds didn't had the core but more later...

The first three pictures show the mould dismantled with a finished raw cap inside and the raw cap in single pictures. On some caps the rods from the feeder heads and risers are already broken off.

 

[Alpini]

Next step was to cut off ~1 cm from the rod on top of the cap where the feeder head was broken off because in this area the rod wasn't round enough (no picture of this small step). Now the remaining length of the rod could be used to hold the cap in collets on the lathe. I used ER-40 collets in a home made chuck on my lathe because I don't own a original collet set for this lathe and such a set - if offered - can be more expensive than I paid for the whole lathe.

Picture No.4 shows a cap mounted in a collet ready to be "calibrated" inside with a special made drill. As mentioned before the first mould had no core so the inner cavity had to be bored out. That's why I made this special drill from pre-hardened material (which was absolutely terrible to machine). Same drills but much more professionally made were used by the industry to calibrate the inner cavity of forged steel shells as seen on the second attached picture (from the NARA).

Some caps were so nice inside that it wasn't needed to use my drill.

Picture No.5 shows the cap after turning it's base with a radius turning tool being ready for cutting the thread.

 

[Alpini]

To cut the thread I made a thread tap from pre hardened material. I don't know it's values but it's hardness is a little below that it is possible to remove material with a file. That's quite hard enough to make some thread in soft aluminum. If I need taps to cut threads into steel I use a material called "silver steel" (Silberstahl) in Germany (1.2210 / 115CrV3). This material is easy to harden at home but still needs some tempering. But heat treatment is still a lot easier than HSS for example which is almost impossible to do without special equipment.

As the rotation of my lathe don't stop quickly a just centered the thread tap on the lathe and finished thread cutting in a vice. But it is very small force needed and could be done with one hand.

Now after the inner side of the cap is finished we have a small problem: How to hold the cap on the lathe to machine the outside? The solution is quite simple: When the lathe was still set up for turning the thread tap I took a short piece of 30 mm bar material and turned also a short thread on this bar. Now the bar can be clamped in a three jaw chuck or better in collets and the cap simply needs to be screwed onto this rod (last picture).


@BMG50 if you need pictures of the production of the tap let me know but I don't want to show here because these are to much pictures and they are a separate small project I think (production took ~1 h only).

An off-topic question:

Is it:

alumium,
aluminum or
aluminium?

My word book is listing all three. I am confused

Continued tomorrow...

 

[kiwieod]

it depends where you come from
the americans say "a loo mi num"
english say it like we spell it,aluminium

 

[Eggburt1969]

An off-topic question:

Is it:

alumium,
aluminum or
aluminium?

My word book is listing all three. I am confused

Continued tomorrow...

Ah, the Aluminium, Aluminum debate

Aluminum was the original name. This later changed to aluminium, which eventually became the official International Union of Pure and Applied Chemistry (IUPAC) name. The American Chemical Society and hence the US, went back to and adopted the older name as that was the more common in use at the time. Only the US and the Canadians still use that version, which is now (after 1993) an accepted variant on the IUPAC official name. Further details in the link below.

https://en.wikipedia.org/wiki/Aluminium#Spelling

Please don't get me started on the way people pronounce technetium!

PS I've no idea where you get 'alumium' from?

 

[Alpini]

Ahh, thank you. Now (not in the middle of the night) I see the words are tagged 'br.' and 'am.' and 'alumium' as obsolete. I got it from dict.cc which was hit No.1 when I was searching for it.

 

[Alpini]

The next step is machining the complete outside shape. The simple method would be to meassure the angle of the cap's cone and setting the upper support of the lathe to this angle and turning down the material until the largest diameter of the cap is correct. That's pretty easy and fast but the round nose still needs to be machined. In my early machinists days I made a radius template from a piece of aluminium sheet metal and turned the nose "free hand". I used an sharpened old file as turning tool same as it is done in wood-turning. Later I build a radius turning tool for such work but in some situations it wasn't very universal.

An other way would be to use a CNC lathe but I don't have the place for one and my old lathe I don't want to ruin with CNC attachments.

So I chose the historical way like it was done a hundred years ago - I build a tracer attachment for my lathe. Professional tracer attachments work with a very complicated hydraulic circuit and require an hydraulic aggregate. And those I have seen for sale were all very heavy and large. There are some nice videos in Youtube about a home-made tracer attachment which is using a simple "feeler mechanism" with a pneumatic cylinder for feed. What I don't like on his construction was that he needed to remove the spindle of his support (time consuming) and also the pneumatic cylinder for feed because it works well only on soft material like aluminium. So I changed the construction in that way that I can mount it instead of the upper support with only two screws and I replaced the pneumatic cylinder by something like a knee-lever (used an old spade handle). I know it's not a beauty but as you see it works very well. The only thing which needs to be improved is the template holder in the background because the aluminium profile isn't strong enough and it bends a little bit when used. So to describe it's function in short words: on the template holder in the background an original fuze cap is mounted with it's non corroded good side to the front and a 20 mm steel rod with a 10 mm ball bearing is transfering the shape to the lower support in front. The upper support is only used to change the actual diameter (cutting depth). The automatic feed of the lathe and also the screw cutting feed can still be used. So it also would be possible to turn british tapered fuze threads with this tool. Instead of using an original cap as template of course also sheet metal templates could be used. Also a very nice feature is to mount simply a short piece of round material to the template holder. This way all sizes of radii can be turned in almost any situation. For operation with automatic feed of the lathe active only one hand is needed to gently push the spade handle forward. Even when turning steel a force not much more than ~30 N is required. One general rule for usage: The turning tool and the feeler must have exactly the same size and shape otherwise the copy would differ in shape to the template.

So here it is and some pictures how it works for the fuze caps:

 

[Alpini]

Finally only two holes were missing in the fuze body: one 4 mm hole for the fuze key and one smaller hole for the set screw (a 8-32 UNF if I remember right). When making multiple pieces the construction of a drilling template is very useful. Together with the depth limiter of the drilling machine such a drilling template improves speed and accuracy a lot and also untrained personnel can be employed . Such drilling templates were commonly used in all shell and fuze factories.

The original set screw can be used in the finished cap and also the original inner Aluminium plate will fit well. The thread size of the cap is 1" x 1/24" Withworth.

The last picture shows a relatively good condition cap in comparsion so a reproduced one.

So that's it. I hope you found my thread about "experimental archaeology" at least in some points useful. I can survive it if our home shop machinists won't start building their own tracer attachments now but for me it increases the possibilities of my lathe by 1000%. Sorry for the thread being very metal working weighted and feel free asking questions there are no secrets.

 

[Snufkin]

An illuminating write-up. Thanks for taking the time and effort.

 

[Alpini]

Update No. 1 - Cap production using templates

As the title says instead of copying an original cap directly this time I will show a more advanced way using templates (curve pattern).

The missing part was a steel cap for the Doppelzündschraube C/86:

 

[Alpini]

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:

 

[Alpini]

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.

 

[Alpini]

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)

 

[Alpini]

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

 

[Alpini]

The last pictures are showing the finished primer screw, the complete fuze and the three tools made for this small project. :ciao:

 

[DICKAREN]

Another great job Stefan.
Richard