Cylindrical shell
From PyroGuide
Cylindrical shells are said to have been in invented in Italy, centuries ago. Hence, they are also known as 'Italian shells'. They are easier to make than round shells. The pattern of stars (or 'break') produced by a cylindrical shell tends to be somewhat less symmetrical than that of a round shells. Because of their simple construction and because there are no stars involved, salutes are often constructed as cylindrical shells. An interesting variety of the cylindrical shell is the multibreak shell, which consists of a number of cylindrical shells, stacked on top of each other and interconnected with time fuse. These produce a number of breaks at regularly timed intervals.
Please note that this tutorial does neither represent a description based on common shell-building techniques, nor assemble a cylinder shell in the proper meaning of the word. Instead it provides a technique to make a more or less successful bombette. Readers aiming at more established methods of shellmaking are referred to upcoming articles!
[edit] Materials
 Casing Burst charge Stars Timefuse Glue String Rammer or wooden dowel Core |
[edit] Construction First step is construction of the casing (if you already have a pre made casing then skip this step). Cut a length of paper about 20-25cm long and place this on a flat surface (the length of cut will depend greatly on the thickness of your paper). Now take your rammer or wooden dowel and roll the paper around it until you achieve 1 revolution. Place some white glue on the paper near the rammer (see picture) and continue rolling for another 1 revolutions. Your biggest problem will be telescoping. That is, as you continue to roll, the paper tape will start to run off to one side or the other. If this happens carefully unroll and start again. Add some more white glue to the paper in a zig zag shape and roll the paper until you have about 1 cm remaining. Place a small line of glue close to the edge and finish rolling the paper. Hold it in your hand tightly for 30 seconds or until the glue has set and the paper does not undo when you let go. You can add a small piece or paper tape to the edge if you wish to aid this process. Remove the casing from the rammer and set aside to dry. |
 Next we need to construct the 'core' of burst charge. As previously mentioned you can use a paper core however a plastic drinking straw is quick and easy. Cut a 1-2cm length of visco fuse and 3cm length of drinking straw. Place a very small amount of hot glue about 3/4 of the way along the visco fuse and insert inside the drinking straw, attaching it to the inner wall. Now seal this end of the straw with a blob of hot glue. Wait until it has cooled and then fill the remaining space of the straw 3/4 of the way with your burst charge and do not compact the powder. If the powder is loose it will burn much faster. Add a very small amount of hot glue to the top of the straw and squash it down on a solid surface to seal the top. Trim the top of the straw with a pair of scissors to obtain a neat finish. |
 Slide the casing back onto your rammer until you have about a 5mm void at the top, as this will be where the disc will be inserted. To make your cylindrical disc, take some cardboard and place your rammer vertically on top and draw a circle line around the base. Cut out the circle with some scissors and repeat the process again until you have two round discs. The two end discs should be made from non corrugated cardboard and should not be too thin. |
 Place a disc into the void and put a ring of glue (white glue or hot glue) on the surface of the disc. Fold over the sides of the casing and press the casing firmly on a hard flat surface for a few seconds until the glue holds well. Drill a hole in the end disc large enough to slide the fuse through. |
 Take your 'core' of burst charge and place this (fuse end first) into the casing and feed the fuse through the hole. To get a symmetrical break, arrange the stars evenly around the sides of the 'core' of burst charge. When full, sprinkle some black powder between the stars to fill up the voids between them. This will act as a sort of prime and help ignite the stars before the shell burst open throwing the stars into the night sky. |
 As we did previously, place the end disc inside the top of the shell and press it down gently until it comes into contact with the stars. Put a ring of glue (white glue or hot glue) on the surface of the disc and fold over the sides of the casing. Press the casing firmly on a hard flat surface for a few seconds until the glue holds well. |
 All that remains is strengthening the casing with string, called 'spiking'. With larger shells the string is often tied to the fuse to start, but this is not a good idea with these small shells since it may fold the fuse, reducing it's reliability. You can instead hold the string in place with your fingers during the first wrap, and wrap it over itself to hold it into place. Make sure the string goes at least 8 times over the length of the casing and then 4 - 6 times around the sides as tightly as possible. Wrap the string over itself again to finish, and secure the knot with a drop of hot melt glue. |
[edit] Cylindrical shell usesThere are varying uses for the cylindrical shell i.e. mortar, payload for black powder rocket etc. |
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Black powder rocket |
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The fire transfer hole in the end plug is primed with a bit of loose black powder, and the shell is attached to the casing with tape or hot glue. The time fuse of the shell must be adjusted for this purpose. Normally, the fuse of shells is long enough to allow the shell to reach maximum altitude when shot from a mortar. When used as a heading for a rocket as shown here, we would like the shell to explode virtually immediately when ignited since the rocket itself already provides the delay. Therefore, a very short length of time fuse should be used in this case. For the example use 5 mm of visco, giving a delay of less than half a second. |
[edit] References
Wouter's Practical Pyrotechnics
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