Comets

and maybe a little about crossettes and splitting comets 

WARNING AND DISCLAIMER:  If you are underage, then consult with your parents or guardians before attempting any of this.  You are on your own - I'm not responsible for your actions or harm you may bring to others because of your actions.  Making the items described below  can result in injury or death to you or people in your vicinity. Some things mentioned here may be illegal to make in your city, county, state, or country so check the laws that apply to you before you attempt anything described here. These notes are not complete on purpose. If you are reading them and new to pyrotechnics, then you are making a mistake. Stop now - this page is not for you. Get a beginning book on fireworks (see Skylighter or American Fireworks News (very quick shipping)  for a start) and read up. You can't make any of this work without more information so read up or join a club or ask someone to help you.

Making a Small (1.5") Comet

Here is the bulk of the tools needed to make a comet. Essentially, a comet is a big star and you make one with a big star pump. The various plugs in the photo above fit into the tube which is charged with Comet mix. The whole thing is pressed onto the metal base. A wood base also works and you can use Bondo or casting resin to cast the plugs. The center rod can be removed to make a solid comet.

Here is a close up of the tube. It is a Schedule 80 1.5" tube which has been beefed up with two sleeves. A Schedule 80 tube has a smaller I.D. than a Schedule 40 tube so it makes a great mold for the comet. Pump one here and it will fit nicely in a Schedule 40 tube.

Here is a scruffy puck of Blonde Streamer that was pressed up and then trimmed a bit. Two of these were pasted together with NC and BP mix (see compositions.html) to make the shot on the right. As a rough guide, the height of the finished comet should be more than half the width of the tube - this to stop it from turning inside the tube on launch. It is better to make small pucks and stack them - they dry quicker.

This comet was fired from a 1.5" PVC tube. The lift was 2.5 grams of Benzolift which is equivalent to about 4 grams of 2Fg.  Click on the picture to watch it go up. It was made with Bleser's Blonde Streamer mix (see compositions.html).

You can use a comet puck to liven up 1.4g fireworks. Here is a small mortar shell with a Blonde Streamer hot glued on top. Click on the picture to see the results. .5 grams of Benzolift were added to the lift cup to help the shell up. That seemed to be about right. Look at the video and see what I mean.

The comet will ignite from just the fuse going past it so it doesn't have to have any fancy linkages. Just glue the puck on the nose and enjoy. You'll notice in the video that the flash on the ground is fairly bright - that's because the comet is burning inside the mortar tube before it exits.

Here is another video - done for another reason - that also shows a couple of smaller comets on 1.4g shells. These are 3/8" thick and 1.25" wide. locustpinecomets.wmv  and are charcoal comets with no metal.

Small (1/2") Crossettes
This example uses Skylighter 68/20/12, ball milled, with +5 dextrin and +10 Ti

The following is a short section (still in work!) about how to roll a 1/2" crossette using Wolter tools. Richard Wolter makes fine pyro tools that are reasonably priced. Check his site out: http://www.wolterpyrotools.com/  I recently came into possession of several of his crossette and comet tools so I started to experiment with small crossettes.  

A crossette is a comet with a four pronged shaped hollow core (a cruciform shape) that is filled with flash or whistle. When the crossette leaves the mortar, it looks like a comet - as it rises up, it suddenly breaks into (typically) four pieces that form a 'plus' sign in the sky. The crossette star tool has a thin metal pin on the end of it that extends into the composition (see pictures below). This pin is the fusing device that determines when the crossette will break. More composition above the pin and the break will be later. Less and it will be sooner. Rich Wolter's tools do not allow the pin to be adjusted so you have to either drill extra stop holes in the plunger (which would vary the amount of composition over the pin) or speed up/slow down the composition.  

To charge a crossette pump, wet the star composition as little as possible - 5% water is a start. If it is slightly too wet, it will stick to the tool (even the new Nituff tools that Rich sells). With the comp in a shallow pan, press the crossette pump into the composition until the cross pin in the plunger rises about 1/2" above the sleeve. Put the pump on a solid wood surface and press the plunger down to compress the comp using an arbor press or a mallet. Make sure the cross pin does NOT contact the top of the pump. After compressing, pick up the pump and push the plunger down with your fingers until the cross pin touches the top of the pump. Trim off the bottom of the tool. This process insures that each crossette is exactly the same size. Pull the pin on the plunger and push the plunger through and slowly draw the crossette off the former. Do not twist.

Problems with crossettes include unreliable break altitudes, no break at all (sometimes called a 'jet') and a break that is too hard. Crossettes are just plain finicky!

Here is a movie of a 'jet': Click here

 Crossettes are a tough to get tuned in and these were no different. Here is what I did to get a reasonably consistent crossette that broke at about the same time and with the same strength: 

 

Crossette compositions for small ( 1/2" or so) crossettes should not be 'soft'. This example uses Skylighter 68/20/12 with +5 dextrin and +10 Ti. This makes a very hard shell (that clinked like china when dry). A press or mallet can be used. This is a faster comp than some streamer comps so there were initial 'early' breaks. The solution was to extend the crossette nose a bit. See #2.


The crossette was extended about 1/4" to allow for the faster comp. This was done by drilling another stop hole in the plunger that was 45 degrees off center with the first and 1/4" (center to center) below it. The above picture shows the tool with three total stop holes. Normally, there is just one.

The nipple was fused with Chinese paper fuse (a nice full diameter piece - lots of BP drooling out of it). Logically, one would think that fusing the nipple wouldn't be required since it has flash in it. However, a fuse causes the flash to ignite more reliably. At least that is what the big boys down at the pool hall say.



The center was filled with 4Fg coated with flash (25% 4Fg, 75% 60/40 perc/al). The intent was to make a relatively safe mixture (ok... relative!) that also flowed easily. However, it was somewhat unreliable and a much hotter flash (but less of it) was probably needed to get more consistent results. Flash is not my favorite mix.


The sides were taped tightly with 2-3 layers of masking tape, capped with fiber board (or wood chip) and the fiberboard end was hot glued.

The bare end was primed with NC and meal.

So far, *most* every crossette I've tried using the above formula has broken correctly. However, there is still a lot of room for improvement and the use of hotter flashes is simply not my cup of tea. So... Rube Goldberg to the rescue!

Mandarin Shots
This example uses Skylighter 68/20/12, ball milled, with +5 dextrin and +10 Ti

Another way to make a crossette is to put a small firecracker - either homemade or purchased - in the shot hole. Putting a Chinese firecracker in the shot hole, it is rumored, is the origin of the term 'Mandarin shot'. In my experience, shots are much more reliable in all ways than shotless crossettes but they are still a pain to make. A traditional (handmade) shot is a work of art in itself. See "Traditional Cylinder Shell Construction" by A. Fulcanelli in Pyrotechnica IX and XI for a great treatise on how to roll traditional shots.  

Click below to see and hear one made with a Chinese firecracker. It is merely one of the above crossettes with a very small firecracker in it. Small firecrackers are too long for the basic Wolter 1/2" crossette so this one was made from two crossette plugs. One plug caps the plug with the firecracker in it and they are glued together with NC lacquer. This stacked crossette (with a hollow core that holds a firecracker) is taped with a couple of layers of masking tape. The end of the crossette that the firecracker fuse is closest to is left bare, primed and fired. 



Splitting Comets
This example uses Skylighter 68/20/12, ball milled, with +5 dextrin and +10 Ti

While the above stunt will make perfect crossettes (much of the time), they still take a long time to concoct. The following picture story shows how to make something that is called a 'split comet' that doesn't break in a perfect 4 pieces but looks great anyway. In addition, it is very easy to construct.

The above tools are simply reworked rocket motor tools. The core is untapered 9/32" stock that is a little over 1" long. You can get stock like that on eBay or you can turn down 3/16" stock.  You can also use 1/4" stock but it makes things very tight.

A 1" wide by 2" aluminum rod with a 1/2" hole in it is used like the cardboard tube would be used in a rocket motor.

Tamp the aluminum case with about 1 1/2" of slightly moist composition. 

This shows brass and aluminum tooling but wood doweling can be substituted (just like for rockets). 

The bottom looks like this (it separates easily from the coring). You can see the round plug inside the 1/2" hole.

Press out the plug using the solid tool or a 1/2" piece of dowel. A drill stand, arbor press, or similar can be used to force the plug out of the case.  Put the tool against the *closed* end of the plug - not the end with the hole. If you are mighty and pure of heart, you might be able to do it by hand.

You get a round 1/2" plug with a 9/32" hole in it. The hole should be at least 1" deep and preferably about 1 1/8". Pretty neat, eh?

Dry the plug thoroughly ( a day in the dryer or a few days on screens). Tape the plug sides only and not the ends

Trim the fuse on a 1/4" x 1 1/2" firecracker to about 1/8" and put it in the hole. Seal it with hot glue. The part sticking out is mostly clay bulkhead so it doesn't take part in the pop at the top of the comet's arc. The bottom of the plug is bare and is primed with NC and meal

Here are a few already made

Above is a jig to make 11 at a time. Essentially, it is 11 sets of tools combined into one block. Each comet is loaded individually but having them all in one pile like the above speeds things up by double or triple. The block can double as a star press for 1/2" stars.

If you use 1/4" stock instead of 9/32" stock, then be careful and not force or twist the firecracker in. The clay seal at the front of the firecracker is brittle and if it breaks, the chances of a jetting comet instead of a splitting one are significantly heightened. Most 1 1/2" firecrackers are not precisely 1/4" so you can usually search through a pack and find ones that fit a 1/4" hole - but a 9/32" hole fits nearly any firecracker you will have..

Click the above image to see the result. Even these comets can jet - but they are usually reliable.