Fan Shaped Multi-shot Homemade Fireworks Firing Boards
Multiple shot pyrotechnic effects boards are a great way to add interest and variety to any backyard or professional public firework display. Although it is easy to pick from hundreds of Chinese made multi-shot cakes for this same purpose, having the ability to custom tailor your own homemade fireworks firing boards is an advantage. This article will focus on constructing the homemade fireworks firing board or "rack" in the manner commonly used by American manufacturers and not the methods favored by the Chinese. American pyrotechnic effect boards typically are made up using a heavy particleboard base and spiral wrap mortar tubes that are hot melt glued into the base. These tubes are generally self-supporting and since they are separated from one another by an air space, and in the rare case of a single tube self-destructing, the remaining tubes will usually retain their integrity and continue to properly function. This is not the case with closely packed Chinese style construction methods.
While this article will not cover specifically how to load various pyrotechnic effects into the mortars, it will give a detailed description of what actual commercial production methods are used to manufacture these pyrotechnic effect boards. Covered topics are the layout and drilling of the homemade firework firing boards, gluing and setting in the tubes, a simple tube fanning technique, and methods for timing the shots (from slow-paced to several tubes fired simultaneously).
GENERAL EQUIPMENT REQUIREMENTS
Circle cutter - Sometimes referred to as a fly cutter, it works by having a high speed steel cutting bit mounted in an adjustable arm that can be slid in or out to vary the cutting diameter. A pilot drill in the middle keeps the device centered in the work piece. General Tools Mfg. Company makes an inexpensive model sold at home improvement stores. Make sure the one you buy uses a 3/16" cutting bit and either the 11/64" or 1/4" pilot bit. Closely follow all instructions printed on the package, especially the one about "Not for use in hand held power drill."
Drill press - The drill press needs to run slow enough for the safe use of the circle cutter (500 R.P.M.) and have a depth stop adjustment. It must be solidly bolted down or heavy enough to prevent movement when in use, for larger boards a 16" or larger model works well.
Tool grinder - In order to use the circle cutter, the end of the 3/16" high speed steel tool bit must be reshaped to cut a flat bottom circular groove in the particleboard to receive the end of the mortar tube. The tool bit supplied with the circle cutter has an angled cutting end, which needs to be reground to a square tip, in order to produce the flat bottom groove. If thin wall mortars are being used the width of the tool bit also should be reground to produce a narrower groove. The width of the cutter should be about .030 - .060" wider than the wall thickness of the tube. For those not familiar with sharpening and reshaping tool bits, it is recommended that someone be found who has some knowledge in this area to avoid potential problems.
Electric skillet - Skillets, in conjunction with hot melt chips are the best way to apply adhesive to the mortar tubes in order to secure them to the particleboard base. Glue guns can be used if only a few boards are going to be made up, but they tend to be very slow and do not give good, even coverage on the tube. Hot melt chips can be purchased in bulk at a much cheaper price than glue gun sticks. Select a skillet with the highest wattage you can find (listed on the side of the box); 1200 watts works fine. Normally the hot melt chips' working temperature is about 350 degrees Fahrenheit. If the melted glue just barely smokes, it is at the right setting on the heat control. The glue must be run at the correct temperature without burning to give the best adhesion to the tube and board. Too cool a setting will make the glue thick and less able to penetrate the pores of the materials being joined. After use, the hot melt can simply be left to cool in the skillet and re-melted at a future date. Glue that has been overheated and burned (it will be a dark brown color) should be discarded.
Biscuit Joiner - A biscuit joiner is a power tool used by cabinetmakers to form moon shaped slots in the edges of boards (wooden biscuit shaped inserts are glued in the slots to hold the boards together). The tool is useful for cutting connecting slots between tubes in the pyrotechnic effect boards. More on this later, it's great if you have one, but not absolutely necessary. A circular saw or router can also be used.
LAYING OUT THE PYROTECHNIC EFFECTS BOARD
The first step is to determine the size and number of tubes you wish to use in your homemade fireworks firing board. Generally 3" I.D. tubes and smaller can be easily used. Since this can be a custom layout, don't be afraid to mix sizes also. For the sake of this article, we will use a 2" I.D. x 10" spiral wound tube (Skylighter #TU2200) with a 1/8" wall thickness. Nine tubes will be needed.
- Using a table saw or circular saw, begin by cutting out a 12" x 12" square of 3/4" underlayment particleboard or medium density fiberboard. Plywood can be used but is harder to groove with the circle cutter and is more expensive. Do not use oriented strand board (OSB board).
- On the surface of the board, lay out in one direction 3 parallel lines spaced 2-3/4" apart and centered on the pyrotechnic effect board. At right angles to this, lay out 3 more parallel lines, again 2-3/4" apart and centered. You should wind up with a grid of lines that intersect at nine points that are centered on the homemade fireworks firing board.
- Set up the circle cutter in the drill press to produce a circular, flat-bottom groove in your pyrotechnic effect board that is 5/16" - 3/8" deep. The groove should be wider than the wall thickness of the mortar tube by .030 - .060. The tube fit will be quite loose and there should be a gap between tube wall and the wall of the groove both inside and out. Use scrap board while making the necessary depth and diameter adjustments. A WORD OF CAUTION: When securing the tool bit in the circle cutter it is absolutely imperative that the pilot bit starts cutting in the board before the tool bit does. The cutting end of the tool bit must be mounted 1/8" - 3/16" higher than the end of the pilot bit. Under no circumstances attempt to use a circle cutter in any position other than perpendicular to the surface being cut. Failure to observe these points will result in the particleboard being forcibly thrown from the drill press.
- Drill nine grooves in the pyrotechnic effect board by locating the pilot bit of the circle cutter in turn over each of the nine intersections previously drawn. Use a slow feed rate on the drill press, especially when the tool bit first enters the surface of the pyrotechnic effect board. Clamping the pyrotechnic effect board to the table of the drill press is highly recommended when drilling each groove. Safety glasses are mandatory. When finished, you should have a 3 x 3 matrix of circular grooves with roughly 3/8" - 1/2" spaces between them. Starting at the lower right and ending in the upper left, label the grooves 1 through 9.
- Using the biscuit joiner (or a circular saw or router) set the blade depth to 9/16" and center and cut slots between positions 7-8 and 8-9. These slots will be used to form a kind of "quickmatch" connection between tubes to allow instantaneous firing of three tubes in a row. Imagine a kind of "underground tunnel" which goes from inside one tube position, under the bottom of the tubes, and comes up inside an adjoining tube. An alternate fusing method is offered in step #10 for those who do not want to try cutting these slots in the pyrotechnic effect board.
SETTING THE MORTAR TUBES
- Lay in a 2-1/2" long piece of black match in each slot cut by the biscuit joiner. The slots, where they cross the sections of circular grooves, should be slightly deeper than the bottom of the grooves to allow the black match to pass under the bottom of a seated mortar tube. Take some lightweight paper (20#) cut roughly 1-1/4" x 3/4", fold lengthwise in half several times and force down into the slot on top of the black match with a narrow blunt stick. Center the paper in the slot. The paper keeps hot melt glue off the black match when gluing in the tubes.
- Have the hot melt glue ready in the skillet. Position the pyrotechnic effect board (assuming you are right-handed) to the immediate right of the skillet with holes 9, 8, 7 at the back of the pyrotechnic effect board. Dip a tube straight down into the hot melt to a depth of 1/2", withdraw from the glue and scrape the bottom of the tube along the edge of skillet to remove excess hot melt. Immediately position the tube over the required location on the pyrotechnic effect board, in this case, the upper left-hand spot, number 9. Generally it's easiest to fill the pyrotechnic effect board left to right, back to front. Since we are making a fan shape rack, this tube will be angled to the left about 10 degrees. To do that, slide the tube straight down in its groove first and then angle to the left 10 degrees (you can cut out a 10-degree cardboard triangle template to lean the tube up against). Since we are not making any attempt to angle the groove into the board or cut the tube at angle, this angling method becomes limited as to the amount of fanning possible, especially with larger diameter tubes.
- Continue filling the pyrotechnic effect board with tubes. Number 8 goes in perpendicular to the pyrotechnic effect board. A quarter twist of the tube as it is being seated gives a nicer bead of hot melt at the junction of the tube and the pyrotechnic effect board. Tube 7 is angled to the right, 4 to the left, 5 straight up, and 6 to the right. At this point the inner row of tubes (4, 5, and 6) must be fused before tubes 1, 2 and 3 can be glued in place. Failure to do so now will make it impossible to fuse them later on.
- After the hot melt has cooled, using the awl, punch visco fuse size holes between tubes 4 and 5, 5 and 6, 6 and 7. The holes should be located just above the hot melt bead about as low as possible on the tube. Holes should enter between the tubes at a 45-degree angle relative to the grid lines on the pyrotechnic effect board.
- Cut visco fuse about 2-1/4" long and thread into the punched holes to connect the tubes together. Three pieces will be needed for this step. There is no need to run visco between tubes 7 and 8 or 8 and 9 since they are already fused with black match, if you have followed steps 5 and 6. If you did not use the "underground tunnel method of fusing in steps 5 and 6, you will have to drill or punch larger holes between tubes 7 and 8 as well as between 8 and 9,so that short pieces of quickmatch can connect the tubes for simultaneous firing.
- Finish gluing in tubes 3, 2 and 1, and continue to run visco between 1 and 2, 2 and 3, 3 and 4. Tube 1 also receives a leader piece of visco as a point from which to light the pyrotechnic effect board, a dab of hot melt on the leader will keep it in place.
- You should now have a fan shape, 9-shot pyrotechnic effect 2" I.D. tube array. The fusing is arranged so that tubes 1-6 fire in sequence with approximately 3 seconds of delay between tubes; tubes 7, 8, and 9 finish the sequence by firing simultaneously.
FREQUENTLY ASKED QUESTIONS
Q. Can I use the pyrotechnic effect board over again after it has been fired?
A. Yes, as long as the tubes and glue joints appear in good shape, the pyrotechnic effect board can be used over again. The setup can be re-fused several times, however, the tube configuration must allow getting to each tube in order to be able to re-fuse it.
Q. The tube is only inserted 5/16" to 3/8" into the pyrotechnic effect board. Is that enough to adequately plug the tube?
A. Yes, since the tube wall is being held both inside and outside by the slot cut in the particleboard, this arrangement is more than strong enough to plug the tubes.
Q. I have some tubes that have walls thicker than 3/16". How can I use them if the tool bit is only 3/16" wide?
A. Easy, first adjust the circle cutter to cut the inside diameter on all the holes needed, then adjust the cutter bigger and go back and re-cut the holes at the new setting.
Q. Don't I have to glue in all the pieces of Visco fuse:
A. No, only the leader fuse needs to be glued. The rest will stay in place just fine as long as the holes are not overly big.
Q. I don't have a tool grinder to grind and reshape the tool bit. Is there anything else I can use?
A. A belt sander with a good quality medium or fine grit belt can be used. When using this or a tool grinder it is very important not to overheat the tool bit. If the tip of the tool bit turns brown it has been overheated and will become dull quickly.
Q. Okay, now I have this great looking homemade fireworks firing board all nice and ready to go - what can I load it with?
A. Just about any idea is fair game, from shells, to mines, to comets. Even small-scale Cremora type or liquid type fireball projectors can be made.
- Replace some or all the visco fusing with electric matches to create very precise electrically fired displays. Although the matches can be placed in the desired tubes by simply making a large enough hole in the side of the tube for the match head and protective shroud, a better method is to install them before the tubes are glued to the board. Here is a good technique: First drill a 5/16" hole to a depth of 1/2" in the circular groove of the mortar tube in which you intend to have the electric match. Next, with masking tape, tape down the match and shroud so that the end of the shroud points at the small pilot hole in the middle of the; circular groove, routing the match leads down into the 5'16" hole and out again. Finally, glue the tube in place as usual. The 5'16" hole allows the match lead to go down and under the tube lip, while the hot melt will seal everything in place making for a very tidy appearance. Do not use a bare match head installed in this manner! Loading a shell or comet in on top of a bare match head could set it off by impact. Even with the protective shroud in place, use extreme caution when loading effects.
- Use fast visco (similar to the type used on class C re-loadable shells; Skylighter #GN1100) to fuse between tubes for a faster pace.
- The technique of using a circle cutter and hot melt with skillet to produce tubes-on-a-base is very fast and versatile. Using simple drilling jigs to produce the hole pattern on the boards, a single worker can drill 500 to 1,000 boards a day. The technique is also good for making single shot baseboard and then cutting the strip into individual blocks.
- #5 mortar tube, 2" diameter (TU2200)
- Biscuit joiner or router
- Black match
- Circle cutter
- Drill press with spindle stop
- Electric skillet
- Hot melt glue chips
- Ice pick or awl (TL4002)
- Particle board 3/4" thick
- Table saw or circular ("Skil") saw
- Tool grinder
- Visco fuse, green
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