Subject: The tiny shell
From: <Saved by Microsoft Internet Explorer 5>
Date: Mon, 22 Jan 2007 01:46:32 -0800

The tiny shell

Like the name implies, a tiny shell is just like a normal shell, only
smaller. Many people already are familiar with film-cannister shells. This tiny
shell is a lot like a film cannister shell in the sense that it is just as small
(or smaller even) and it's effect is more or less the same (a small shell). It's
construction is quite different from a film cannister shell though. Tiny shells
are made with more traditional materials such as paper, string and glue. Also, I
believe these shells break more symmetrically with less energetic burst (I use
black powder) than the film cannister shells (which require that the lid is
glued on real tight and even then you will need a flash break).

The materials

- A burst charge. For example black powder, which is much more safe
to use than flash powder, but can give a bad break if your casing is flimsy. In
my experience, flash didn't give a better break in these shells than black
powder, so IMO there's no point in using flash. Another reason I prefer black
powder is that flash can disturb color perception if the flash is too bright.
Ofcourse, if you use stars that are based on a chlorate composition (which is
strongly discouraged for beginners) black powder burst should never be
used.
- Stars. Either round or cylindrical (pumped/pressed) stars. It is
ofcourse possible to use cut stars, but since the shell is cylindrical, round or
cylindrical stars are more practical. Ofcourse, the stars can't be large.
Somewhere between 5...10 mm, depending on burn rate.
- Timefuse. Fuse made
from visco is fine. You can use any kind of timefuse, but visco is cheap and
works nicely.
- Kraft paper. If the artists paint supplies shop doesn't have
kraft, use brown paper shopping bags.
- Glue. White glue or your own
favourite glue for contructing the casing and hot melt to seal the fuse. You can
use white glue instead of hot melt, but hot melt is easier/quicker to work with.
Since you will only need hot melt for sealing the fuse when it's not inserted in
the shell yet, there's no real safety advantage to using only white glue.
-
String. Hemp string is traditional. You can probably use any kind of strong,
thin string. Nylon for instance works well too.

The casing

For a casing you will need a cardboard tube, and two cardboard end
discs (see picture 1). You can ofcourse use premade tubes, but it is easy enough
to roll your own and the advantage will be that you can make them any size you
like and fits your mortar tube(s). The diameter of the shell will be determined
by the dowel you choose to roll your casings. If you have a 4 cm diameter
mortar, choose a 2.5 cm diameter dowel. The extra space is for casing thickness,
string and some extra to make sure the shell doesn't fit too tightly.

A casing is made by rolling a strip of paper over a dowel while
applying glue. It is simple, but it takes a little practice to roll smooth,
strong casings. Some hints: if your casing is wrinkly, try using thicker
(heavier) paper, and/or apply less glue. If you use wallpaper paste, make sure
it isn't too wet (don't follow the instructions on the package; use far less
water). Press the dowel firmly on a flat surface while rolling to prevent air
gaps. Don't forget to apply glue to the sides of the paper! Once you rolled the
whole strip of paper, trim the sides with a sharp knife. The tube should be 2 to
3 times long as it is wide. For a 2.5 cm diameter dowel, Keep rolling untill you
have a wall thickness of about 2 mm.

The two end discs should be made from non corrugated cardboard and
should not be too thin. I have no access to real thick carboard, so I use a
thinner variety and glue two discs together to obtain a single disc that's twice
as thick. The discs should be the same diameter as the dowel you used to roll
the casing over.

Now, place one end disc on the dowel, and slide the casing over it,
leaving about 0.8 cm extending over the end disc. Put some glue on the end disc,
and fold over the sides of the casing. Press the casing very firmly on a hard
flat surface for a few seconds untill the glue holds well.

The contents

Use whatever you think will look good. Try combinations of colors,
effect stars, changing stars, salutes etc. I think small stars are best: the
effect will last a little shorter, but the density of the break will be better.
If you use slow burning stars, about 5 mm diameter, the effect will last a
second or three which is usually enough to appreciate the color or effect. You
can ofcourse always launch several in a short time to lengthen the effect. To
get a symmetrical break, it is a good idea to arrange the stars along the sides
of the casing and use a 'core' of burst powder as illustrated. Sprinkle some
fine black powder between the stars to fill up the voids between them. Using a
core may not be necesarry if the casing is strong enough and using more stars
will improve the star density further.

The timefuse

Like mentioned in the materials section, visco fuse works fine for
this. It's cheap, small and reliable. I' ve launched quite a few tiny shells and
so far have not had a single dud or flowerpot. And I usually don't even prime
the visco. The visco needs to be partially wrapped in paper for this purpose.
Use a 7 cm long, 1 cm wide strip of kraft paper with some white glue on it and
wrap it tightly around the visco. If you make the paper strip wider, the delay
will be longer. Make sure at least 0.5 to 1 cm of bare fuse extends from the
paper on both sides (picture 3).

Now take the second end disc and drill, cut or pierce a 3 to 4 mm
diameter hole in the center. Stick the fuse through this hole, and seal it well
with hot melt glue. Let the hot melt cool well before proceeding with the next
step.

Finishing the shell

Place the end disc with the fuse, hot melt side up, in the casing.
Tap the casing and press the end disc firmly on the contents. This will make the
shell a little more rigid and resist the 'kick' from the launch better. Put glue
on the end disc and fold over the casing. Press firmly to make sure the glue
holds well.

All that remains is strengthening the casing with string. With larger
shells the string is often tied to the fuse to begin, 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 fuse in place with your fingers during the
first wrap, and wrap the string over itself to hold it into place. Make sure the
string goes at least 8 times over the length of the casing and then 5 - 8 times
around the sides. Make sure it is regularly and evenly spaced; this will improve
the symmetry of the break. Also, wrap it around the shell as tightly as you can
without cutting your fingers with the rope. You hands will get tired from this
very quickly, after 4-5 shells.

Once the stringing is done, write on the shell what's inside so that
you won't forget if you make several.

Launching the shell

You will need a mortar that is a few mm wider than the shell. There
must be 3 to 4 mm extra space between the mortar wall and the shell on both
sides. Also, to reduce the amount of work of making a shell I ommited the lift
bag/cup that is often used with larger shells. Instead, I use 4 cm diameter HDPE
mortars with a fuse hole in the side and simply dump 3 to 4 grams of black
powder in the mouth of the mortar, followed by the shell. This works fine.