How To Realize Perfect 5" Shells.

[MinamotoKobayashi]

Hello forum.

Here is the third chapter of my tutorials: how to realize perfect 5 inches shells.

This tutorial is the continuation of my previous tutorials

 

https://www.amateurpyro.com/forums/topic/13028-how-to-make-hot-granulated-r-candy-mix/

and

https://www.amateurpyro.com/forums/topic/13154-making-very-performant-nozzleless-r-candy-rockets-with-my-granulated-mix/

 

First of all we needs two 5" hemis. Often the cheap chinese hemis are not perfectly rounded, so it is necessary to arrange the shape

pressing them between our hands in the right places to make the shape as round as possible:

 

With the help of a coarse sandpaper sheet smooth the edges making them flat and uniform, without smudges or bosses:

 

With the help of a drawing pin create a tiny spot at the center of the hemis:

Hint: probably it will not be the definitive hole, so do not make it too deep.

 

To be sure that we have made a centered hole, trace a circle near the edge of the hemis with the help of a compass.

If the traced line is not parallel to the edge, You must vary the spot position:

 

To paste a near perfect circular shell, we must trace three circles:

As NeighborJ suggested me, the compass aperture must be: 25mm for the first circle, 46mm for the second and 65mm for the third.

 

Making an hole for the straw:

 

Inserting a straw:

 

Gluing the straw with a good mastic:

Hint: after applied the mastic, push the straw with Your finger just enough to make it protrude 2-3mm from the opposite side, and then reposition it:

in that way some extra mastic will adhere to the straw and make the junction more solid. You can see the result in the above shot.

 

Placing the stars inside the hemispheres:

Hint: keeps the smaller stars last, so You can place them easily to fill perfectly both the hemis.

 

Spread some coated rice hulls over a tissue paper foil:

For every 100 grams of rice hulls I use 500 grams of fast BP meal and 200 grams of KP meal as booster, applied as last layer.

Hint: You can easily obtain tissue paper foils manually separating the paper layers from a paper towel

 

Placing the bag inside the shell:

 

Arrange the tissue paper:

 

Adding some extra CRH:

Hint: if You put too few CRH, the stars will shake inside the pasted shell and there is a concrete risk that the stars move from their original position

creating a not simmetrical aperture. If You put too much CRH, You must not be able to close perfectly the two hemis. You must found the sweet spot.

Usually a small hill of CRH should be ok.

 

Cutting the unneeded tissue paper around the equator with the help of a pair of scissors:

 

Taking another tissue paper foil and making a little hole at the center (the same diameter of the straw or better slightly smaller):

 

Inserting the straw inside the hole:

Hint: let the straw out as shown in the picture. Do not press the sheet further or the outermost stars will roll down!

 

Spreading some CRH over the tissue paper foil:

Hint: make little increments with the help of a small tea spoon.

 

Lift the edge of the tissue paper foil and check if some stars came out of their original position.

If so, please reposition them correctly with the help of a stamp tweezers:

 

Two hemis ready to be joined:

 

Wrap one of the two hemis with a sheet of tissue paper and tighten it firmly with one hand:

 

Turn the hemis upside down and place it on the top of the other hemis:

 

While rotating the two joined hemis, gently hammer the upper hemis with the help of a rubber hammer or other suitable tool.

The ideal hammering points are limited from the 25mm and the 46mm circles, so while rotating the shell, move the hammer

up and down, longitudinally:

Hint: if You place the hemis in a hard surface, there is the risk that the other hemis will be damaged, so place it in a softer surface, like between Your thighs

 

If everything was fine, the shell should look so:

 

Since the joint of two shells is the weakest part, I prefer to put some wood Titebond glue inside the crack:

Edited January 16, 2019 by MinamotoKobayashi

[MinamotoKobayashi]

Applying 20mm gummed paper around the equator as first layer:

 

Applying a pressure of some kilos with the help of my hydraulic press for 24 hours, to join perfectly the two parts:

Hint: please use paper washers as shown in the photo to avoid any hemis deformation.

 

Marking the tiny hole to easily recognize the spot during pasting:

 

Applying the second layer:

 

Applying the third layer:

 

Applying the fourth layer:

 

Applying the fifth and last layer:

 

To make the pasted surface smooth and free of frills and clews, place the shell over a hard and solid surface, rotating it and changing often the direction

of rotation, maintaining a certain pressure with the hand itself.

It is advisable to do it on the ground to avoid dangerous electrostatic charges:

At the end of the procedure the shell should exhibit a smooth professional look:

The shell weight should be between 700 and 800 grams:

 

Adding a tiny bit of fast BP meal to ensure a perfect path between fuse and CRH:

 

This is a superfast Visco fuse (about 1 meter/second). Since we do not need time fuses (the timer will be set inside the rocket, please refer to the rocket thread),

this kind of fuse is ideal.

With the help of a small pair of scissors it is necessary to cut the fuse lengthwise for a few mm, remove the coating and expose the burning part (both the ends):

 

Carefully insert the fuse thru the straw until it stops:

Hint: place other small pieces of fuse between the main fuse and the straw to keep everything in place.

Hint2: You must found the correct lenght of the fuse. It must be made in such a way that the part of fuse that will be inserted inside the rocket must adhere perfectly

against the r-candy flat surface: the exposed part of the fuse will have to enlarge its threads against the surface and thus offer a broad and solid contact.

A too short fuse do not allow fire continuity, and a too long fuse it could bend too much and move the exposed part away from the propellant surface.

 

Gluing the inside part of the rocket with hot glue:

 

Join firmly the two parts until the glue harden (30 sec is enough):

 

Removing, with the help of a cutter, the glue in excess and finishing the part with a turn of 20mm gummed tape:

 

The finished firework. Soon the video

Edited January 16, 2019 by MinamotoKobayashi

[justvisiting]

What a mountain of work you did, to photograph and post all these steps! Thanks for sharing your method so freely.

[NeighborJ]

Yes, and your rockets look amazing.

[Zmuro]

Your tutorial are always well documented and straight forward. Thanks for sharing.

[Aspirina]

Thanks for share this tutorial is perfect

 

One question:

 

 

100 grams of rice hulls I use 500 grams of fast BP meal and 200 grams of KP meal as booster,

I understand that you are making the CRH in a star roller or something like this? 5 parts of bp and 2 parts of kp for 1 part of rice hulls? (kp in the last layers)

Edited January 24, 2019 by Aspirina

[BlueComet24]

Nice work! I can't wait to see it launched. One thing I would personally do differently is to use a hand-rolled paper straw just to cut down on plastic pollution, and perhaps tear the tissue to keep scissors away from live comp.

[MinamotoKobayashi]

X Aspirina: nope, I follow this tutorial:

 

http://blog.skylighter.com/fireworks/2012/02/making-black-powder-coated-rice-hulls.html

 

Yes I use 1 part of wetted coated rice hulls, 5 parts of fast BP and 2 parts of KP as last layer.

This create an hard shell break. If some stars gone blinded of destroyed, please reduce to 1 part of wetted rice hulls, 6 parts of fast BP and 1 part of KP.

 

 

xBlueComet24: first the real detonation inside the shell will be generated a tremendous heat that surely evaporate instantly the small plastic straw

Yes tear the tissue is safer, especially when You're playng with perch mixes!