Firework Making

Fireworks! What fun! Watching them is great, and I find making them and watching your own creations is even more fun.

I wrote an article on making fireworks with three ace fireworking friends, and Make Magazine published it. You can see the article here, and it is called Making Fireworks.

A jig for making: The Double Petal Ball Shell

Introduction

I have made a jig for easy creation of double petal ball shells: an inner burst of stars, surrounded by an outer burst of different stars. This page describes what it is, and how to make the jig, and how to use it in constructing a double petal shell. Video of this shell

I got inspired to do this by Cliff Pearson, a master firework maker and teacher of fireworking techniques. I also received inspiration for this project from Ned Gorski, on his wonderful site fireworking.com. Here is a video of a bunch of double petal shells made with this jig, made by myself and others.

A Jig of Wood

I found out about making double petal shells from Cliff Pearson about 2 weeks before the big Winter Blast firework convention put on by the The **Western Pyrotechnic Association** in Arizona.

I pumped Cliff for information on how to do it on the phone, then looked at fireworking.com for more tips, and came up with this jig to make it all easier.

The jig holds a half ball of wood suspended into the Hemi shell, so that burst powder can be placed inside of the outer layer of stars, and saving space for the inner layer of stars. Follow the link to the WoodJig page for instructions on how to make this wooden jig. The instructions for the 3D printed jig are below.

Here and at the top are 6” shells made with this jig.

A 3D Printed Jig

Another way to make this jig, inspired by Cliff, is to print it with a 3D printer. So next I designed a variation of this jig and printed it on my 3D printer.

A 3D print is a perfect way to make this. Once it is designed, one merely prints the pieces, glues them together, and there you have it. This is designed for a 6 inch ball shell. By using the scaling functions of the software, jigs can be made for other sized ball shells. I think 6 inch shells are a great size for this. I made wood jigs for 5” and for 6” shells, and the 6” shells were so much fun that the 5” jig did not get used much at all. The 2 7/8 inch diameter half ball with its attaching connection is screwed to the upper crosspiece. This way, different sized balls can be used, even giving the possibility of making a triple petal shell. If you don’t have a 3D printer, it is possible to have a 3D printing service print them for you (or consider making the wood jig, which does the same thing).

The design of this 6 inch jig was done with Autodesk Fusion 360. This program is free for hobby use. My Fusion 360 design file may be accessed by downloading BallShellJig4. This includes the design file that can be opened in Fusion 360, and also the stl files that are ready to print. The ones with disks have “mouse ears” on the corners to aid in sticking to the print bed, especially useful if you print in ABS. The disks are easy to trim off after printing. The stl files may be used with a slicer program to load into your printer, or uploaded to have the parts made for you. The bottom pieces are printed with supports everywhere for the overhanging lip that rests on the edge of the hemi, but the horizontal holes for the eye screws are blocked from supports with support blocker. The other parts are printed with no supports, and are almost all printed right side up, except the ball is printed with the round part facing up, and the ball connector is printed with the gluing pegs up. I used 3 mm wall thickness, and 35% infill. For ABS I used a bed heated to 100 degrees C, glass bed covered with a layer of Kapton tape, and MagiGoo Original as an adhesive. The printer is enclosed. Nozzle temperature is 243 deg. C. I printed two bottom pieces together, and the crosspiece, ball, and ball connector together in a separate print.

3D Printed pieces

Four pieces are ready to fasten together. Two circles of wood are made to hold the bottom supporting pieces in correct position, and the crosspiece has matching holes for the pegs sticking up from the lower pieces.

Gluing the pieces

Wood circles are 5 5/8” and 6 3/8 “ diameter. Pieces are put onto the wood circles, and test lined up before gluing.

You could also draw the circles on a piece of paper and clamp the lower pieces onto the circles. There are pegs in the bottom pieces that mate with holes in the crosspieces to help line it up. For ABS, they are glued with clear PVC glue, sold for gluing PVC pipe. For PLA, roughen the glue surfaces with sandpaper and glue with epoxy. Wet both surfaces in each glue joint before assembling.

There are holes printed in the sides to place the eye screws. The size of the holes is important. If they are too small then the plastic will crack when screwing in the eye screws. They are drilled out with a #2 drill (0.221”). The eye screws are brass, as steel screws would present a danger from possible sparks, which could be a big problem while working with explosives!

My jig is printed with ABS plastic. It has good strength, and also slight flexibility to help prevent cracking when putting in the eye screws. Using PLA plastic will probably work fine, especially Tough PLA, but you need to be careful with the plastic softening and distorting if left in a hot car. The holes need to be just the right size for PLA to avoid cracking the plastic when placing the screws. The eye screws didn’t seem to be available in brass machine screw threads. Stainless steel is probably OK, but some people think there is a small spark hazard, and it may depend on the alloy of the stainless steel. There are some nice knob screws available for a big jump in price. The brass eye screws work well, and require no tool to tighten. Again, don’t use steel! Steel and Stainless Steel are two very different alloys.

Brass eye screws www.mcmaster.com part number 9497T36

The brass wood screws for attaching the ball are brass #8 x 1.5 inches flat head wood screws. The holes in the crosspiece are drilled out with a #19 drill (0.166”) for a loose fit of the screw shank, and the holes in the ball connector (glued to the ball) are drilled out to a #26 drill (0.147”) to engage the threads of the wood screws.

Making A Shell

The half-ball that is attached to the jig has a hole in it to go around the passfire tube. A layer of Loctite Adhesive Spray inside the hemi makes the stars stay in place very nicely. I used my wood jig for these pictures. The 3D jig didn’t get made until after the convention, so I will have to wait until the next event to get pictures with the 3D version. Living in California, I can’t be making fireworks at home!

Below are pictures explaining the construction of the shell. Hover over or click on a picture to see the text for that step.

The hemi is loaded with the first layer of stars.

A larger ball half is wrapped with tissue, and placed into the stars, to get the tissue down into the hemi without disturbing the stars.

Now the ball half is removed, and some burst powder is put into the bottom of the tissue.

Tissue is wrapped around the half ball of the jig, and the jig is fastened into position. Burst powder is packed into the space with a wood dowel.

The tissue from around the ball is spread out, and the jig is removed. Fast-drying spray lacquer on the tissue helps stiffen the tissue (optional), and then spray adhesive helps hold the stars in place.

Now the inner petal of stars is loaded.

Similar to the first layer, a smaller tissue-wrapped ball is used to get tissue inside the layer of stars.

Now burst powder is used to fill the inside.

I had so much fun making these shells, that I didn’t want to make any more single petal shells. Twice as many stars, and more is better! Two kinds of stars means prettier fireworks.