How to Make End-Burner Rocket Motors

“Give a person fireworks, and you make them happy for a day.
Teach a person how to make fireworks,
And you make them happy for a lifetime.”

There are three common types of simple, black powder, charcoal-tailed, rocket motors: cored, nozzleless, and end-burner.

A cored black powder rocket motor is the traditional motor, typically with a clay nozzle, and a hollow core going up through the nozzle and into the fuel grain for some distance. This is how the typical sky rocket is constructed. If you take the nosing off the bottom of a commercial sky rocket and look up into the end of it, you’ll see about a half inch tall ring of clay, which forms the nozzle, and then a longer core going up into the black fuel grain.

A nozzleless motor is a fairly recent development as far as I know, and it has no clay nozzle, but does still have the core going up into the fuel grain. It uses a hotter fuel than the cored rocket motor.

An end-burning motor has a clay nozzle, but no core going up into the fuel grain. The fuel burns only from its end, and this type of motor typically uses a hot fuel and has a smaller hole, or aperture, in the clay nozzle than does a cored motor. Often, full strength 75/15/10 (potassium nitrate, charcoal, sulfur) black powder is used as the fuel in these motors, and typically the diameter of the nozzle aperture is one quarter of the inside diameter of the motor tube (3/16″ nozzle aperture for a 3/4″ ID rocket tube).

It is this latter type of motor, the end-burner, which I intend to use to test the power of fuels made with 5 different charcoals in an upcoming article, Some Notes on Experiments with Various Charcoals.

The nice thing about these motors is that they burn for a fairly long time, up to about 10 seconds, with a constant amount of thrust. That thrust varies considerably from one charcoal to another, in my past experiences.

Below is a shot of a motor that I carefully sliced in half with a hacksaw, outdoors. You can see how solidly the fuel packs when dampened just a bit, with no separation between fuel increments. You can also see how the top of the nozzle is shaped to direct the flow of the burning gasses smoothly out of the hole.

End burning motors are useful for more than just rockets, though. They can be used as short duration gerbs (fountains, pronounced like the first part of “gerbil”), or as drivers on wheels or girandolas (horizontal flying wheels). When I want metal sparks in the motor’s exhaust, I add 6% fine ferro-titanium or spherical titanium powder to this homemade rocket fuel.

The methods for making end-burner rocket motors are very similar to the ones for making regular gerbs and less powerful wheel drivers. Those devices typically are made on a larger diameter spindle, and their fuels are less powerful than the rocket motors.

For the homemade rocket fuel, I’ve made 75/15/10 ball-mill-dust using each of 5 charcoals (See Ball Milling 101
for details), and now I’m going to make 3 end-burning rocket motors using each type of mill-dust.

After milling, I add 1-3% water by weight to my mill-dust fuel, and screen it in well, to minimize dust during the ramming process, and to produce a very hard, solid fuel grain. Most folks do not dampen their fuel prior to making rockets. Some just use the mill-dust as-is. Some dampen it, then granulate it through a screen and then allow the granules to dry, thereby cutting down on the dust.

During the dampening process, I find a bit of difference when it comes to how much moisture each type of fuel needs to dampen it a bit. The willow and commercial hardwood mill dusts each required 1.5% or so….Whereas the other 3 charcoals required about twice as much water to achieve the same degree of moisturization. I know the fuel has enough water in it when it stops being dusty and free-flowing.

I press my motors in standard, 7.5″ long 1 lb. (3/4″ ID) rocket tubes. If I am using full-strength, hot black powder I use strong-walled tubes from New England Paper Tubes. These tubes are very strong and resist side burn-through. For weaker powder, I can use Skylighter’s standard 1 lb. rocket tubes. During the pressing I find that each motor requires 3 oz. of fuel for all the charcoal mill dusts, except the whitewood charcoal, which only needed 2.75 oz. of fuel to fill the tube.

Here’s a quickie tutorial on pressing end-burning motors. We covered Making Nozzle Mix in an earlier article. Here are some end-burner spindles and rammers, from Steve LaDuke and Rich Wolter (wolterpyrotools.com).

The tapered-end rammer with the hole in it is for pressing the nozzle, and the flat end rammer is used to press the fuel.

There are various types of tube supports which can be used when ramming or pressing motors, but I don’t find them to be necessary when using a mallet to hand ram these motors. I do use a support when pressing motors on a hydraulic press. (See notes on presses in Nice Shells in 2 1/2 Days, Part 2). Here are two types of commonly used tube supports. The reason they are used is to prevent the paper tube from splitting under the extreme pressures of hydraulic pressing these motors.

Before I ram the nozzle, I plug the hole in the spindle with the end of a bamboo skewer, and then install the tube onto the spindle.

Then I ram the nozzle using 1/2 tablespoon of the nozzle mix, with 8-12 good blows with my rawhide mallet. Each time I add an increment of fuel, I ram with the same number of blows from my mallet, using approximately the same force each time. It is important to keep the hole in the tapered rammer cleaned out.

I then pull the spindle out of the tube, remove the bamboo, insert a doubled piece of thin blackmatch which projects out of the spindle 3/8″, and re-insert the spindle into the motor-tube to ram the fuel.

You might notice that in the photo of the different spindles above, there are two types of spindles which are identical except one type has holes in them, and one does not. If you have several tools like this, you can press the nozzle with the solid spindle, remove it, insert the other spindle with the blackmatch inserted in it, and then press the fuel. This eliminates the need for the bamboo plug.

The blackmatch gets embedded into the fuel grain for a very reliable, ignition priming system. This is a piece of one of the five strands of thin blackmatch that can be found in flat quickmatch.

The fuel is rammed, about a tablespoon at a time, to within 1/2″ of the end of the tube, and then a clay bulkhead is rammed on top of the fuel.

If a header is going to be installed on the rocket, a drill bit is hand-twisted into the clay bulkhead mix
to create a “passfire” hole. The passfire simply directs fire from the burning rocket motor to the contents of your header. A header can be a star shell, or any other pyrotechnic effect that you can get your rocket to lift.

A simple rocket heading can be made with some aluminum-foil duct-tape, 1/2 teaspoon of FFg BP, and some stars.

I like to use two sticks on a rocket for balance. Home Depot sells some nice 1/4″ x 3/4″ pine lattice which works well for these little motors. Sticks are necessary, because without them, the rocket will not fly in any particular direction. Sticks act like a kite-tail. They help your rocket fly straight.

The last step is to add some visco fuse to your finished rocket. Just cut a 4-5-inch length and insert it in past the blackmatch all the way into the nozzle. Your fuse should fit into that hole snugly and not fall out.

For years, these motors performed very consistently for me. Then, while making and testing the motors for this article, some of them started to blow up on me, obviously exerting too much pressure in the motor tubes.

Well, “Dang It.” I had changed something: either the potassium nitrate I was using, or the charcoal, or the darn alignment of the stars in the heavens. But something had changed and now my new batch of fuel was too hot, too powerful.

This is an all-too-common experience in fireworking. It can be minimized by consistent manufacturing techniques, and the use of consistent quality and type of chemicals. Unfortunately, we hobbyists do not usually buy large quantities of chemicals, so, as we re-supply, variations can be introduced, resulting in the type of problem above. (You can reduce this problem by shopping with reputable vendors who carry the same grades of materials for years.)

This ends up requiring and cultivating diligence, persistence, flexibility, patience, and carefulness in the budding fireworker, as we recognize and work to solve these problems. Meticulous note-taking will help you reproduce successful results. Unless you record everything you do, it will be next to impossible for you to achieve success repeatedly.

The fuel that is currently too hot for my motor tubes was made from ball milled black powder, using a combination of willow and pine charcoals. I have milled up quite a few batches of this fuel and now have a 5 gallon bucket of the fuel, which has been thoroughly mixed so it is consistent throughout.

I know that fuel made with commercial airfloat charcoal is less powerful than the above fuel, so I mill 2 batches of it. My plan is to make up some fuels which are mixtures of the above two fuels, until I hit on a proportion of the two which results in a high-performance motor which does not blow the tube to smithereens.

I have an electronic scale I use to measure rocket thrust, to be detailed in a forthcoming article, Some Notes on Experiments with Various Charcoals. I also time the motor-burn with a stopwatch.

I have found in the past that a reliable, powerful motor burns for 9-10 seconds with 1.3-1.5 pounds of thrust. Beyond those parameters, the motors start to blow up.

I ram a motor, made with fuel containing only commercial airfloat charcoal. It burned for 12.3 seconds and produced .9 pounds of thrust on average. (This is better performance than I’ve had in the past with this fuel, so apparently this new batch of potassium nitrate that I’m using results in a more powerful BP.)

Next I ram a motor with 3 parts of the weaker, commercial charcoal fuel, above, and 1 part of the hot fuel containing the pine/willow charcoal. This motor burns for 11.5 seconds with 1.15 pounds of thrust.

The next motor has 50/50 of the two fuels, and it burns for 10.8 seconds, at 1.3 pounds of thrust. We’re gettin’ somewhere. This motor, with this amount of thrust is usable for a driver or girandola motor.

I want to end up with nice, consistent, high-thrust motors, but not have them at the edge of blowing up with some of them failing. I have a 40-motor, 36″ girandola planned for this summer. I’m going to enter it in the competition at the Pyrotechnics Guild International’s annual convention in Gillette, Wyoming; I don’t want it to fail because some of the motors blow up.

I decide to try one hotter motor, stepping up to 1 part of the slow fuel, and 2 parts of the fast fuel. This motor burned for 10.5 seconds and had a bit over 1.4 pounds of thrust. It also had that “sound” of a motor being on the edge of blowing up.

I’m going to back off to the 50/50 ratio of the fuels, press up 9 motors with ferro-titanium in them as I would with girandola motors, let them dry out for 2-3 days, and then re-test them to make sure they are working consistently with that fuel mixture.

When these motors were dry, I took them out to my testing grounds and burned all of them. Three of them, mounted on the digital-scale test stand, burned for 10.5 seconds, with an average of 1.2 pounds of thrust, and they were all consistent.

Then I launched the rest of the rockets with and without headers, and with sticks of various lengths on them, so that they each had different weight payloads. Typically these motors fly well when their thrust is 2.5 to 3 times the total weight of the rocket.

For a 1.2 pound thrust (19.2 ounces), then, a rocket ought to weigh in the 6.4 – 7.7 ounce range. This is also the way to calculate how much a girandola ought to weigh, depending on how many drivers are on it.

For the above girandola example, with 40 of these drivers, the total thrust will need to be 40 x 19.2 = 768 ounces. The final ‘dola ought to weigh between 256 and 307 ounces, or 16-19 pounds. The lighter it is, the faster it will climb and the higher it’ll fly.

Of the sample rockets in this current batch that I launched, all flew well when their total weight was 6 -7.75 ounces, and they failed to fly well when their weight was 8 ounces or more. The above calculations would have predicted that.

I think that these motors, rammed with 50/50 cool/hot fuel have enough thrust, but are not near the “edge” where there is a risk of a percentage of them blowing up.

In the next article, I’ll be using these end-burning rocket motors to test black powders made with the 5 different charcoals.

Till then, have fun and Stay Green,

Ned

Firework Shells in 2 1/2 Days – Part 4

“Give a person fireworks, and you make them happy for a day.
Teach a person how to make fireworks,
And you make them happy for a lifetime.”

This is the final installment in a series of articles chronicling my efforts to produce two traditional 8″, Tiger-Willow, paper ball shells, including handmade stars, burst powder, spolette time fuse, lift powder and quickmatch, all at a weekend pyro event.

The original series of articles ran in 2007 in the Pyrotechnics Guild International’s Bulletins #152-155, and this is a somewhat revised and expanded re-issue of that series.

Part 1 – How to Make Charocal, detailed the charcoal options for this project. It included the production of homemade charcoal to be used in the various components of the firework shells. The charcoal-making step of the process would occur at home prior to travelling to the pyro get-together.

The next article addressed ball milling materials, skills and techniques.

In Part 2, production of the black powder (BP) shell burst granules, black match, shell lift powder, and charcoal tailed stars were begun. Options for star rollers, drying chambers, hydraulic presses, star plates, and homemade shell casings were also discussed.

And then in Part 3, I addressed granulating the black powder, priming the stars, making spolette time fuses, and assembling and pasting the firework shells.

Now it’s time to finish these shells up and get ready to put them into the air.

Well, the shells are dry in the drying chamber. Today I will “lift and leader” them, and tonight fire those babies up, two and a half days after starting this project.

Making Match Pipe

My 8″ mortar is 42″ long on the inside, so I’m going to want two quickmatch shell leaders about 48″ long. The leader is the fuse which leads from the shell at the bottom of the mortar, up and out of the mortar (the “gun”). The leaders for large aerial fireworks shells are typically made of quickmatch, which is black match inserted into a paper tube called match “pipe.”

To make match pipe for these leaders, I roll 3″ x 34″ pieces of 40# virgin kraft paper around a 3/8″ x 36″ aluminum rod (or you could use a wooden dowel), gluing the edge of the paper down with white glue. This will produce double wall pipe.

First, I tear a 34 inch long sheet from my kraft paper roll. Then, I fold the paper in 3 inches from the edge, make a crease, and slice it off in the crease with my sharp knife. I then make a fold the length of this strip, about a half-inch in from the edge. I lay the aluminum rod into that fold, then roll the paper around the rod, pressing and rolling it on my table a few times till the paper is snug around the rod. At this time, I glue the edge and press it down.

If you look at the bottom of a typical Oriental ball-shell, you’ll notice that the shell lift powder is contained in a conical, paper covering called a shell lift cup.

I have made a little former and template to use in making the shell lift cups.

These are based on the lift cups I have seen on some commercial Firework shells. I use the template to cut out a pattern of 60# kraft paper. Then I stick a 2″ chipboard disc on top of the former, wrap the kraft around it, and hot glue the kraft to itself and the disc, creating lift cups as shown.

Making the Quickmatch

I want two 50″ pieces of quickmatch for the shell leaders. I’ll be using 1-1/2 pieces of the match pipe for each leader. I like to put two pieces of black match into each pipe to insure flame propagation past any potential weak places in the black match.

After gently unrolling the dry black match off the match frame, I cut four 54″ pieces of match. First, I insert two of the pieces into a 34″ piece of match pipe. Then I slide a 17″ piece of the pipe onto the match, inserting the end of it about an inch into the longer pipe, and taping the joint well with masking tape. That produces a 50″ piece of quickmatch with black match sticking out of each end.

Lift Powder

Now I take the screen of 2FA black powder out of the drying chamber and dump it onto some kraft paper. The BP is divided into two 6 oz. amounts and put into two small plastic baggies.

One end of a quickmatch leader is inserted into the lift powder in the baggie, the baggie is gathered around the match pipe, and a band of masking tape secures the baggie closed. The extra baggie plastic is trimmed off with scissors and the first tape band is secured to the match pipe with another band of masking tape.

Now, on the shell, I mark the pole opposite the spolette. Holding the baggie of lift powder there, I hot-glue the leader to the shell down to the equator.

Then I hot-glue a lift cup onto the bottom of the shell, covering the lift powder.

Note: I am top fusing these shells because they use spolettes, which are more susceptible to pressure and blow-through than time fuse is.

Matching the Spolette

After turning the shell upright, the masking tape flag/cover is removed from the end of the spolette, and the powder core is scratched in an X pattern with an awl. An ‘h’ made from 5 inches of black match is hot glued and tied onto the spolette.

Then the quickmatch leader is brought up to the bottom of the spolette where it is bent and then hot glued to the upper hemi of the shell and the side of the spolette.

I pierce the side of the leader above the spolette and cut a little ‘door’ in the side of the match pipe just above the top of the spolette. Then I insert an extra piece of black match as well as the upper leg of the spolette ‘h’ match into the leader pipe, and cover the junction with masking tape. This insures that a lot of fire is going to be transferred to the top of the spolette when the leader burns to that point.

Then the whole leader/spolette assembly is covered with a kraft paper bucket, consisting of two turns of 40# kraft paper and tied with clove hitches at the top and bottom. I then tug on the leader to make sure it is tightly secured to the shell, since it serves as the lifting rope, which is sufficient for a shell weighing as little as this one does.

Finishing the Shell

The shell leader is ‘S’ folded back and forth onto itself to form a bundle. A band of masking tape, sticky-side-out, secures the bundle, and then the sticky side of that band is covered with a layer of masking tape, sticky-side-in. This forms an easily torn band which is not adhered to the leader. A piece of visco fuse is taped into the end of the leader.

Two of the Tiger Willow stars are hot glued on either side of the spolette to serve as rising tails. Then the tails are covered with rounds of tissue paper, which are tied on with clove hitches, and the labels are glued on.

Note: This method of attaching the rising tails works well with my glitter comets, which are made of a composition which gets very hard when it is dry. The glitter tails stay attached to the shell very well.

The tails used above, being made from a higher-charcoal-content comp, were softer. I accidentally bumped one of them and it popped off. I then re-glued it, and also completely covered the sides of all the tails with a layer of hot-glue, right down to the glue attached to the shell. This strengthened the tails and ensured that they stayed on during the lift and ascent of the shell. Another approach uses masking tape around the comet, then little strips of masking tape going down the comet and onto the shell body.

After about 16 hours of work, I have two 8″ shells. Similar Chinese ones could have been purchased for under $100 or so. Yeah, I guess I’m nuts, but there is something tremendously satisfying about being able to start from scratch, with no pyrotechnic materials, make a little charcoal, get some chemicals, add some paper and glue and string, and end up with these two shells.

I guess that’s what I always wanted to know how to do ever since getting into this art almost 20 years ago. I also wanted to know if it could be done in a weekend.

Acknowledgments

On the above note, I’d simply like to say that, although I’ve written about a few original techniques that I employ, there’s really nothing new in this series of articles.

In my quest to learn how to make fireworks, there have been literally hundreds of generous folks along the way who were willing to share what they’d learned in their own experience. They’ve written books and articles, made videos, given seminars, posted to the pyro email-lists and club mailing-lists, made wonderful tools and equipment to use, made chemicals and materials available, and been willing to converse with, and tutor, fellow pyros eager to learn.

To all of them, I simply say, “Thanks.” We all stand on the shoulders of those who have gone before us.

We all do this to belong to the pyro community. Remember that feeling you felt when you realized you were not alone in loving all of this?

Best Regards,

Ned

Checklist

• Homemade Airfloat Charcoal
• Potassium Nitrate
• Sulfur
• Dextrin
• Wheat paste

  Note: It is possible to make one’s own dextrin and wheat paste from corn starch and flour, respectively. This would further reduce a pyro’s dependence on outside sources of supplies. “Post-Apocalyptic Pyro” may be the way of the future.

• Block of wax
• Denatured alcohol
• Lampblack
• Water
• Puffed Rice
• Pop-up tent
• Tables
• Chairs
• Generator
• Extension cords (3 or 4 100′)
• 4 plug gang adapter
• Gas can – gasoline
• Ball mill
• Ball mill timer
• Ball mill sifting screen/buckets
• Plywood for barricades
• Digital scale
• Plastic tubs
• 5 gallon bucket of water/sponge
• Star roller
• Drying chamber and screens (plus wood strips to rest shells on)
• Possible humidifier
• Rubber gloves
• Spray bottle
• Hose/nozzle
• 12 to 24 strand string for black match
• Roll of 40# virgin kraft paper on dispenser
• Rough 40# kraft
• 60# virgin kraft
• Miscellaneous hand tools/toolbox
• Match drying frame/stand
• Match forming nozzle
• Measuring cups/spoons
• Dust mask/respirator
• 20 mesh screen kitchen colander
• 10 mesh screen kitchen colander
• 4/8/12 mesh sorting screens
• 40 mesh screen
• 12 ton hydraulic press
• Air compressor
• Grease
• Propane torch
• 4″ comet pump
• Aluminum block to use under comet pump
• 5 gallon bucket/lid for mixing comp
• Star/comet plate
• Drywall knives/putty knives
• Meat tenderizing hammer
• Plastic baggies
• 6″ x 6″ x 4′ pounding post
• Small paintbrush
• Paper cups
• Paper plates
• Paper towels
• Spolette tubes
• Shell hemis
• 1/2″ hole punch
• 3/8″ spolette ramming rod
• Small aluminum ramming puck/plate
• Rawhide mallet
• Hot glue gun/glue
• Tissue paper
• Blender
• Large paintbrush
• Plastic cutting boards
• Sharp kitchen knife
• Pasting strip marker
• Shell stands made of pieces of 4″ PVC pipe
• 3/8″ x 36″ aluminum rod or wooden dowel
• Lift cup former
• Lift cup template
• 2″ chipboard discs for lift cups
• Scissors
• Shell labels
• White glue
• Visco fuse
• Masking tape
• Thin string
• Hole punch
• Dust pan/broom
• Stopwatch
• Cooler or low table to paste shells on
• Light to work by if it gets dark
• Plastic tarps to cover work tables with at night or in rain
• Two turtle doves, and
• A partridge in a pear tree

Firework Shells in 2-1/2 Days – Part 3

“Give a person fireworks, and you make them happy for a day.
Teach a person how to make fireworks,
And you make them happy for a lifetime.”

This is a continuation of a series of articles that details the production of good, traditional, paper ball shells in a minimum timeframe, possibly at a three-day fireworks club event. I’m exploring the possibility of arriving at the meet with only a few chemicals, some other materials, some tools and equipment, but with no completed pyrotechnic compositions, and then producing these firework shells from scratch.

The original series of articles ran in 2007 in the Pyrotechnics Guild International’s Bulletins #152-155, and this is a somewhat revised and expanded re-issue of that series.

Part 1 – How to Make Charcoal, detailed the charcoal options for this project. It included the production of homemade charcoal to be used in the various components of the shells. The charcoal-making step of the process would occur at home prior to travelling to the pyro get-together.

The next article addressed ball milling materials, skills and techniques. (Ball milling will be put into immediate action once we arrive at the site and begin actual production of these shells in this part of the series.)

In Part 2, making black powder (BP) shell burst granules, black match, shell lift powder, and charcoal tailed stars were begun. Options for star rollers, drying chambers, hydraulic presses, star plates, and homemade shell casings were also discussed.

Today I want to check on how dry the items in the drying chamber are. I also want to granulate the BP pucks, prime the stars and finish drying them, make the spolette time fuses, assemble the shells and paste them in so that they can dry overnight.

I woke up this morning wondering how everything in the dryer was doing. I opened it up, took two stars out of the top screen, and tapped them together. I’ve learned that when they are pretty dry they produce a crisp, clacking sound like two stones being knocked together. The stars are doing just that.

I then took a couple of the stars out to a safe place and lit them one at a time with the propane torch, tossing them into the air when lit. They both ignited well and burned with nice spark trails, burning out just after hitting the ground. This is just how I want this star to burn.

Back in the drying chamber, under the star screens, I unearthed the screen with the BP pucks on it. I stacked the pucks up and weighed them. Yesterday, I started with 20 oz. of mill dust and added 2 oz. of water, so when the pucks are totally dry they ought to weigh 20 oz. again. They now weigh 20.2 oz, so they have just a bit to go. When the pucks are completely dry, they “clink” when they are tapped together, sounding like pieces of pottery or china. This morning they have a slightly duller sound.

I cut a 6″ piece of the black match off of the match frame and took it out into the field to light it. It was nice and stiff and it burned well and consistently.

And, from one of the bottom frames, I removed a very small handful of the burst granules. Putting them on a rock out in the field, I inserted a 6″ piece of the blackmatch and lit it. Great. A quick poof and the puffed rice cores disappeared in the flame. Good and dry.

Ah, life is good. Warning: I have a buddy who wanted to demonstrate how his BP rough powder burned. He made a pile of it and lit it with the torch. The whole backside of his arm got badly burned. Always test burn compositions and devices by installing a piece of fuse so that you can retreat before it all ignites.

Now I want to crush the black powder pucks and screen the granules into usable sizes. First, I put a puck in a little plastic baggie. Then I put the baggie on top of my 6×6 pounding post and whack it with a metal-headed meat-tenderizing hammer until the puck is busted into about 2FA (about 1/4 inch) size granules.

I do this with all the pucks, one at a time, and dump the BP into a 4 mesh sorting screen.

I sift all the granules out that will pass through that screen, and re-crush the granules that won’t pass through, until all the BP has passed through that screen and onto a sheet of kraft paper.

Then I pass that pile through an 8-mesh screen. The granules that won’t pass the 8-mesh, but have passed through the 4-mesh are dumped onto a paper plate, and are the 2FA lift powder, which will propel the finished shells into the air. (See black powder size charts.)

I then pass the remainder of the powder through a 12-mesh screen, and the powder that has passed through the 8-mesh but won’t pass the 12-mesh forms a pile of 3FA when dumped on a plate.

Doing the same thing with a 20-mesh screen kitchen colander separates the remaining powder into 4FA (same size as FG) and meal powder. What passes through the 20 mesh colander is Meal powder. What doesn’t pass through that colander is 4FA.

I wanted to end up with 12 oz. of 2FA for lifting the two 8″ firework shells, and I actually ended up with 14.3 oz. of it. So I weighed out and set aside 12 oz, and further crushed up the extra 2.3 oz. of the 2FA, along with the 2.5 oz. of 3FA, until it was all sorted into the 12 ounces of 2FA, 4.8 oz. of meal powder and 2.75 oz. of 4FA.

I measured 1 oz. of the meal powder onto a paper plate, and put it back into the dryer to use later in the making of the spolette time fuses. I also spread the 12 oz. of 2FA lift powder out on a screen and put it back in the dryer to insure that it is completely dry when I use it.

Lift Powder Note. I’ve compared black powder made this way with commercial BPs. In tests performed with baseballs shot out of a 3″ mortar, to produce a 300’ high flight (6.5 second flight time up and down, 4.33 seconds of fall from apogee to ground), the following powder amounts were needed:

0.35 oz. 3FA made from pine charcoal
0.45 oz. Commercial charcoal 3FA
0.55 oz. Wano Brand BP 3FA
0.75 oz. Pine charcoal 2FA
0.75 oz. Commercial charcoal 2FA
0.75 oz. Wano Brand BP 2FA

Testing with 6″ dummy shells, 2 lb.-6 oz. shell weight, using 3 oz. of lift, produced the following results:

Willow charcoal 2FA	11.06 seconds flight
Pine charcoal 2FA	11.65 seconds flight
Commercial BP 2FA	12.46 seconds flight
Commercial BP 3FA	13.28 seconds flight

So, I’m confident that making BP with the SPF (spruce/pine/fir) homemade charcoal, or with commercial charcoal, produces results that are comparable with willow charcoal and commercial powders.

Note: In a future article, I’ll be detailing various black powder production methods, and procedures for testing the various powders and comparing them with each other. Stay tuned.

Now I want to prime one end of each star. With the black powder break charge that I’m using in these shells, these stars will probably all light without priming. But I like to be on the safe side. The primed end also adds a bit to the break, and speeds up flame propagation on the star.

I mix 0.2 oz. of dextrin with the 3.8 oz. of BP meal and wet it with some water to make a prime-slurry in a plastic tub. Using a little paint brush, or at other times dipping the end of the star into the slurry, I wet one end of each star with the prime-slurry. Then I press the wet end into the 4FA to form a rough, granular-primed end on each star. It took me an hour to prime all the stars and put them back in the dryer.

Note: The method of priming stars outlined above is not my favorite or standard method. I employed it in this project to speed the process up, since the stars can be primed, dried, and assembled in the shells the same day.

My regular method of priming these 113.9 ounces of stars would be as follows:

• Make a “scratch-mix,” BP prime by screening together:

  Component	Weight
  Potassium Nitrate	24.9 oz.
  Airfloat Charcoal	4.9 oz.
  Dextrin	1.7 oz.
  Sulfur	3.5 oz.
  Total Weight	35 oz.

  (This is a 15/3/2/1 ratio of the ingredients)

  (Referring back to Part 2 of this series, 21 ounces of BP mill-dust, including dextrin, was set aside from the second ball-mill batch. This could be used as part of the above prime. To this 21 ounces, 9.9 ounces of potassium nitrate, 1.9 ounces of airfloat charcoal, 1.5 ounces of sulfur, and 0.7 ounces of dextrin, would be added and screened into the mill-dust to make the prime.)

• Divide the stars into five lots, about 23 ounces each lot
• Divide the prime into five batches, 7 ounces per batch
• Put one lot of the stars into the star roller

  

  Small Star Roller

  (This is assuming that I’d be using my smaller, stainless-steel pot roller. If I was using my larger, cement mixer roller, I would experiment with priming 2 or 3 of the 23 ounce lots or even all of the stars at one time.)

• Out of one of the batches of prime, take 1/4 cup of the prime powder, place it in a paper cup, and add 2 tablespoons of water to it, stirring to mix up a thin prime “slurry.”

• Start the star roller with the 23 ounces of stars in it, and dump the slurry onto the rolling stars, using gloved hands to thoroughly coat the stars.

• Slowly add the remaining dry prime powder out of the 7 ounce batch, 1/4 cup at a time, working the stars with the gloved hand to keep them separated, and spraying with water as necessary, until all the prime has been taken up by the stars and they have a nice, solid, “crusty” looking coating of prime on them.

• Dump that batch of stars onto a drying screen
• Prime the remaining 4 lots of stars in the same manner

The disadvantage of this method, from the viewpoint of this project, is that it takes 24 hours for the stars to completely dry. If I had that extra day, I would employ this method for the star priming.

10:00 am – 12 noon. Take a little break and let the stars and spolette meal powder dry completely.

12 noon – 12:30 pm, Make spolettes.

I’m making spolette time fuses for these shells, rather than using commercial time fuse, because I want to make the shell completely from scratch, using only a couple of chemicals.

Note: From Traditional Cylinder Shell Construction, Part I, Pyrotechnica IX, by A Fulcanelli, “The spolette is the oldest and most versatile type of shell fuse. It consists of a small-bored and relatively thick-walled tube, charged partially with pure commercial meal powder.”

Pyrotechnica IX and XI contain the complete “Fulcanelli” series on this type of shell construction, and those of us who are familiar with this resource can’t recommend it highly enough.

I have found that my homemade BP meal powder, such as that which was derived from the corned pucks above, works very well in spolettes.

My spolette tubes, which I’ve had for awhile, are 3/8″ ID, 1/16″ wall, 2.25″ long, parallel wound tubes. (Skylighter sells some nice spolette tubes which are just a bit larger in OD.) I want 4 seconds of timing for the 8″ shells, and based on Fulcanelli’s figures, that ought to be about 1-3/8″ of solid powder, plus 1/16″ at each end for scratching back, for a total of 1-1/2.”

First, I cover one end of a tube with masking tape and ram it with that amount of powder, using my 3/8″ solid aluminum rod rammer, a little aluminum puck ramming base, my rawhide mallet and my 6×6 pounding post.

I pound 1/8 teaspoon at a time, which produces 3/16″ increments, until I have a solid powder column in the tube 1.5″ long. Then I scratch both ends of the solid powder core with an awl to a depth of 1/16,” and attach a piece of visco fuse with masking tape.

Burning that spolette in a safe location, and timing it with my stopwatch, reveals a time of 3.2 seconds with this black powder. I recalculate the length of the powder core I’ll need for 4 seconds, and arrive at 1-3/4,” plus 1/16″ inch on both ends for scratching back.

I make a spolette with 1-7/8″ of powder, scratch the ends, burn it and time it, and get 4.1 seconds. Perfect. I then pound two spolettes with the 1-7/8″ powder column (this takes 0.2 oz. of powder for each spolette) and scratch the inside powder with the awl. Note that the finished spolette has powder flush with one end of the tube and covered with masking tape, and leaves 3/8″ of the tube still open and not filled with powder.

Note: A friend recently gave me a nice tool set for making spolettes. It is similar to what Rich Wolter makes (wolterpyrotools.com) and may have been made by him. It has been machined to work with the size tubes I am currently using. The grooves on the shaft of the ram, 1/4″ apart, come in handy for gauging the height/timing of the powder column which has been rammed.

I’m using commercially produced, Chinese, strawboard hemispheres for these shells.

My spolette has a 1/2 inch outer diameter. So, using my half inch steel punch, I knock a hole in two of the hemis, using my rawhide mallet and the 6×6 pounding post.

Note: Awhile back I purchased an inexpensive set of gasket punches at http://harborfreight.com/. These punches come in handy for punching holes in stuff like the shell casing above.

I then hot-glue the spolettes in the two hemis, forming nice fillets of glue on both the inside and the outside, allowing 1″ of the flush end of the spolette to stick out on the outside.

I removed the masking tape to insert the spolette. Now I cover the outside end of the spolette with tape again, making a little “flag” with the tape for orientation during the pasting process.

On the inside of the hemi, I take a 5″ x 5″ piece of 40# kraft paper and make a passfire tube with three turns of the paper rolled up on a half-inch dowel. Then I hot-glue the tube over the spolette tube. I’ve enlarged the dowel just a bit with some masking tape to make sure the passfire tube will fit over the spolette tube.

Sighting across the plane of the hemi equator, I use scissors to clip the passfire tube off flush with that plane. I then insert two pieces of black match, making sure they fit down into the spolette tube and are pressed against the scratched column of black powder, and sticking out of the passfire tube about 1/2.” I then tie the end of the passfire tube with a clove hitch, and use my awl to punch a vent into the passfire tube below the string.

Note: here’s where you can see one way to tie a clove hitch knot.

The clove hitch is the most-used and versatile knot employed in fireworking, and there are several ways to tie one. At one time, I spent some time sittin’ in my LaZBoy chair, with a piece of string, and practicing the various ways of tying a clove hitch until they became second nature.

I remove my stars from the dryer and try to pry the prime off of one of them. The prime is very hard and dry, and pulls off some of the star along with it. This indicates it is thoroughly dry and fully adhered.

I like to hot-glue my stars into the hemis with a small stripe of glue on each star, applied to the end opposite the primed end, beginning with the stars at the equator. I use four rings of 4″ PVC pipe as stands for the hemis during this process.

I glue the stars in about 1/8″ below the equator because the angle of the hemi brings the inside edge of the stars just above the equatorial plane, where they will mesh with the stars in the other hemi.

I then fill the rest of the hemis with stars, lightly gluing each one in.

In a few cases I chip off edges of stars with a knife to allow a spot to be filled with another star. (I do this outdoors in a safe location.) Each hemi holds about 72 stars, for 144 stars per shell.

After filling all 4 hemis, I have 215 stars left over, enough for another shell and some rising tails. (I could have made 2/3 of the stars in the original batch if I wanted to avoid having these extra stars to dispose of. Maybe I can rustle up some more BP and make a mine or two.)

I remove the burst powder from the dryer, line the stars in each hemi with tissue paper, and fill the tissue with the burst charge, clipping off the extra tissue paper with scissors. I allow the burst to project above the hemi just a bit. When I mate the two halves of the shell, I want to have to work a bit at doing so, so that, once they are mated, the shell contents are tightly packed in place.

Note: At some point, if you’re like me, you’ll say, “Heck, I don’t need to keep that old burst powder separate from the stars with that tissue paper. I’ll just dump the burst in on top of the stars and work it into the voids.” Yep, that’s what you’ll say, and that’s what you’ll try, and then, after you close the shell and continue to work on it, the burst will migrate further in between the stars, and the burst and stars will start to loosen up, and the contents of your shell will start to rattle around, and your shell burst will look asymmetrical and ragged, or else the shell will flowerpot on lift (break in the mortar when it is fired).

Then you’ll say to yourself, “Well, that was a good experiment and a valuable lesson learned.”

And, you’ll go back to using the tissue paper. Yesiree.

I then close each hemi with a circle of tissue paper, hot-glued to the equatorial ring of stars. This paper disc is easily made by taking a square of tissue paper slightly larger than the casing, folding it in half, then quarter, then eighth, etc, and then clipping the folded paper off to the right length, as shown.

Note: There has been quite a bit of conversation in pyro-circles about the safety of using hot-glue when fireworking. The heat of the glue is not a problem, being well below the ignition temperature of the commonly used compositions. The problem can arise, if and when the hot-glue gun malfunctions, and possibly emits sparks. Some pyros allow their guns to heat up, and then unplug them before gluing.

The general consensus is that the most important safety precaution when using a hot-glue gun is to keep the gun on its stand, or sitting in a “garage,” like a length of PVC pipe, when it’s not in use.

That also keeps its innards from getting gummed up with excess glue, a common cause of malfunction. If one lays the gun down on its side while it’s being used, the excess glue ends up all over it, and some ends up seeping into its bowels. My guns, when used this way are a mess. But when a gun is stored during use with the tip pointing down, either on its stand or sitting in a “garage,” the excess glue just drips off the tip. The glue stays new, shiny as the day it was born, and not all gummed up inside.

It’s also probably a good idea to avoid using those “dollar-store,” el-cheapo hot-glue guns.

Now it’s time to mate the hemis by flipping one of them over quickly and onto the other one, and then setting them tightly against each other by applying pressure with my hand and lightly tapping with my rawhide mallet. Then the hemis are secured together with high-adhesion masking tape.

I know what you’re asking, “Does this guy ever take a break or eat?”

I am determined to get these shells pasted-in and in the dryer before dark and the beginning of the evening’s festivities. And, no, nobody ever accused me of passing up on a meal.

“Pasting” a shell is the process of applying layers of reinforcing paper onto the exterior of the assembled shell hemispheres.

I mix up some wheat paste (the good stuff from pyrosupplies.com) in my blender until it is about the consistency of yogurt. Wheat paste is the old-fashioned wallpaper paste. I know, I know, how would you fellas, who are reading this, know what the consistency of yogurt is? Real men don’t eat yogurt. Go buy a little tub of it and check it out. I like strawberry. (No, you cannot paste your shell in with strawberry yogurt!). But I digress.

I like to paste 8″ shells with 1″ x 9″ strips of 40# virgin kraft paper. I have an 18″ wide roll of this paper in a dispenser. I tear off twelve 9″ long sheets, and do this four times, making 4 stacks of 12 sheets. I am going to use one stack of 12 sheets for each application.

I can only cut through 6 layers of the paper with my sharp knife (which I keep really sharpened). So I paste up 6 pieces of the paper on my cutting board. I apply paste to the cutting board; paste both sides of the first sheet and then lay down the rest of the sheets, feathering them as I go, and pasting only the top side of those 5 sheets.

Now, after marking my 1″ widths with my marking screw-board (there are screws every 2,” and I eyeball the intermediate cut marks), I cut the sheets into 1″ wide strips.

Now I pick up one stack of 6 strips at a time, and lay down 9 of the stacks on top of each other, feathering the ends as I go. Then I roll them up into a little roll.

I do this twice for each cutting board batch, and there are two of these batches for the total of 12 sheets, so I end up with 4 of the little rolls of strips.

By the way, this paper and this method require no “breaking” of the paper. (Breaking paper, as described by Fulcanelli, entails crumpling it up to incorporate the paste and break the grain of the paper.)

The first thing I like to do is to brush some paste onto the shell and smear it around with my hands, preparing the shell casing so the pasted strips of paper will really adhere to it.

I like to apply the strips in the “9 axis system” described by Jim Widmann in his PGI Bulletin article, Bulletin #123, March/April 2001. This system uses the 3 main axes, x/y/z, as well as the 6 intermediate axes, which are rotated 45 degrees from each of the main ones. The little masking tape flag on the spolette is used to keep track of the axes as the pasting progresses.

Don’t worry if this is not immediately clear. I lay awake for a bit on a couple of nights visualizing all of this until the light went on inside my head. The purpose of this system is to rotate the “poles” of the layers of paper, so that the final, consolidated wrap of paper has a consistent thickness and strength.

As seen in the above photos, there are open spaces left at the north and south “poles” left after applying the 9″ strips, and these poles are covered with torn strips of paper.

Each roll of strips is sufficient for one axis application, which produces 2 layers of paper on the shell since the strips are lapped by half over each other as they are applied. So, the 4 rolls are good for the first 4 axes, or 8 layers of paper.

As I apply successive layers of the paper strips, I keep the shell nice and wet with the paste, by applying a bit with the paint brush and smearing it around with my hands.

After applying the first 12 sheets/4 rolls/4 axes/8 layers of paper to the first shell, I place it in the drying chamber, with the shell resting on two strips of wood which lie across one of the drying screens. (The shells may be too heavy to rest directly on the screen, and I don’t want them sticking to it.)

While the first shell is drying a bit, I apply the first 8 layers to the second shell. The first shell has taken about an hour to paste, and it dries for an hour while I’m pasting the second shell. Once this is accomplished, I switch the shells in the dryer and make the second 8-layer application to the first shell, then switch them again, and apply the final 8 layers to the second shell. Now I have 16 layers of pasted paper on each shell.

Sometimes, if I’m getting fancy, I apply a few drops of red or green food coloring on the shell as I’m applying the last layers of pasted paper. This results in uniquely colored shells.

Note: One alternative method for pasting the shells is to use gummed, kraft-paper tape, and a tape wetting/dispensing machine. The tape would be applied to the shells in similar lengths and fashion as the pasted paper above. I like to use 1-1/4″ wide, 35-40# tape on 8″ shells.

The next and final chapter in this series will detail Sunday’s lifting and leadering of the two shells. Then we can take them out to the field and put ‘em up into the air!

Till then, Stay Green,

Ned

Firework Shells in 2-1/2 Days – Part 2

Ball Milling 101

I have some lump charcoal that just came out of my retort after I cooked it, and I want to turn it into airfloat charcoal.

Or, the directions say to ball mill my rocket fuel for an hour.

An article tells me to ball mill my star composition prior to pressing my stars.

Maybe I just got some crystalline potassium nitrate that looks like sugar, and I want to turn it into a fine, talc-like powder.

And, perhaps most of all, I want to be able to make commercial-quality, high-performance black powder.

In Volume 1 of Bill Ofca’s Technique in Fire, he states that “small particle size is important to good chemical reaction. The smaller the particle size, the greater the specific area, hence the most complete and fastest reaction.”

Except for very small batches, ball milling is the best way for the amateur fireworker to reduce particle size in their chemicals. With small batches of individual chemicals, some folks use electric coffee mills to grind the chemicals into fine powder. NEVER grind mixed compositions in a coffee grinder, though. To do so would be to court disaster.

Lloyd Sponenburgh, in his Ball Milling Theory and Practice for the Amateur Pyrotechnician, tells us his explorations into ball milling began when he was faced with having to do all that grinding with a mortar and pestle to achieve small particle size and intimately mix his chemicals. Lloyds’s book is the most complete and practical resource I know for information on ball milling theory and for plans to actually build your own ball mill. Here’s a shot of a nice, double-barrel mill I built based on his principles.

Ball milling replaces potentially unsafe hand grinding of chemicals and compositions. The crushing of the material is accomplished by the repeated falling of heavy balls onto it, over and over, inside the mill jar.

So, it sounds like I need a ball mill. I want my chemicals to have small particle size and be intimately mixed. What are my choices?

I can either get Lloyd’s book and build my own ball mill, or I can purchase one. (I’d still recommend getting the book for all of the other valuable milling information contained in it, though.)

Skylighter sells a nice ball mill which comes with a mill jar. All you have to do is add milling media. More on that in just a minute.

I’m also including how-to info for a few other milling accessories that will increase your milling productivity. You can make this yourself: a bucket screen to separate your milled powders from the media; a simple little soundproof cabinet to put your mill in: and weatherproof sandbags for safely barricading the mill.

Here’s the ball mill you can get here at Skylighter. This size jar is typically referred to as a ‘one gallon jar’ because its volume is, indeed, one gallon.

This jar is constructed of PVC plumbing pipe and fittings per Lloyd’s original instructions.

How many jars or barrels do I need? If one is milling only black powder (”BP”) compositions, or the individual chemicals that make them up (potassium nitrate, sulfur, charcoal, dextrin), then only one barrel is necessary.

If I am milling some other chemicals by themselves such as barium nitrate, strontium nitrate, or ammonium perchlorate, then I want a barrel/media combination dedicated to each of those individual chemicals. This prevents cross-contamination between the various chemicals that are milled.

Black powder compositions are the only mixed chemical compositions I mill, and they are never milled with any metals in them. If, say, a charcoal star formula calls for the inclusion of any metal, such as ferro-titanium or titanium, the metal is added to the black powder base composition after it is milled.

The ball mill consists of the mill base and the mill jar. There’s one more important component to a ball mill, though: the media. The balls of heavy material which fall upon and crush the chemicals are called the milling media. Here’s the media I bought to use in this mill. I got the packages of lead balls from my local gun shop, which sells them as muzzle loading bullets. They can also be purchased online.

It took 12 boxes of these 1/2″ diameter lead balls (from Bass Pro) to fill the mill jar half full, which is the ideal media “charge” in this1-gallon jar setup. The total weight of the media is 30 pounds.

That is an important note: Fill the mill jar half full of media for optimal milling.
If you use less, your milling time will either be longer, or the grinding will be insufficient. The most frequently reported milling problem we hear at Skylighter is from people whose black powder was weak because they did not use enough media.

After I got these lead balls, I ran the mill with them in the jar along with 4 cups of airfloat charcoal I had on hand. This was in order to clean off the oil, grease, and/or wax that came coated on the new balls. Then I threw that batch of charcoal out. I did not want that “crud” to end up in any good chemicals or BP that I milled.

Well, now we have a mill base, a mill jar, and the media to go into it. How much material can we put into the jar, and how can we get started grinding it?

“Well, Ned, we just fill the jar the rest of the way with chemicals on top of the media and turn her on, right?”

“Nope,” said Ned.

For efficient milling, the ideal amount of stuff we are grinding, the “material charge,” is just enough to fill all the voids between the media and then just a little bit more. This turns out to be an amount of material that fills the empty mill jar 25%, or 1/4 of the volume of the mill jar, after the material has been milled.

Now, in practicality this can be a bit hard to determine. How do I know how much lump charcoal to add to the jar to end up with enough airfloat charcoal to fill one quarter of the jar? How can I tell how much potassium nitrate, charcoal, and sulfur will mill into just the right amount of black powder mill dust?

Trial and error, that’s how. I have found that if I put my media in the jar and then add enough of my cooked and crushed lump charcoal to just loosely fill the jar the rest of the way, I will end up with about the right amount of airfloat to fill the voids in the media and cover it by a bit more when the run is done.

It’s easy enough to take your empty mill jar and add individual cups of water to it to determine its volume. Then divide that by 4 and that’s the amount of, say, potassium nitrate to add to a mill jar run to finely pulverize it. You get the idea. The jar and barrel shown above both have a one-gallon volume which is 16 kitchen measuring cups. So, a milled material charge of 4 cups in volume is what we are shootin’ for.

In making black powder, I’ve found that a material charge of 15 ounces of potassium nitrate, 3 ounces of airfloat charcoal, and 2 ounces of sulfur produces the most efficient quantity of BP mill dust.

The density of the mill dust, and therefore the volume it occupies, will vary a bit with the density of the charcoal used. Pine charcoal is quite a bit less dense, occupying more volume per ounce than commercial airfloat. Therefore the mill dust produced with the pine charcoal occupies more space after it has been milled than commercial charcoal would.

But, we’re shooting for a material charge that is approximately 25% of the jar’s volume, and the 15/3/2 amounts that I listed above will be close enough, whatever charcoal one uses. If one is finicky, these amounts can be adjusted with experience and experimentation.

Ball mills are noisy. And there is always the risk of explosion when BP comps are being milled. For these reasons, a remote milling site which is protected from people and property is necessary. Starting the mill remotely, either by plugging in a 100’ extension cord that runs to it, or by setting the mill time on a timer, prevents you from standing next to it while it is running. (Notice the timer in the photo of my double-barrel mill and in the photo below.)

Once a nice, safe, remote location is determined, set up a level platform for your ball mill.

I’ve mentioned that a mill explosion is always a possibility when complete black powder compositions are being ball milled. So, try and place your mill behind a natural barricade like a mound of earth, a rock, or a big tree. If you can’t do that, barricading the ball mill with sandbags, stacks of firewood, 5 gallon buckets of water or dirt, or something similar is a great idea. This barricade will absorb the energy and flying debris in the event of an accidental explosion.

You can see in the photos that I have the mill at the end of an extension cord, on a timer, and nestled against a stack of firewood. I then surround the mill with bags of all-purpose sand that I’ve wrapped with heavy duty garbage bags and duct tape. I want my sandbags to withstand the weather and handling and last a long time.

Installing a tarp to protect the mill and timer from sudden inclement weather is a good idea.

I check my mill temperature now and then during mill runs. I remotely stop the mill (by disconnecting the power cord at the end away from the mill). Then I adjust the vent holes and lid accordingly to maintain a 70-120 degree F temperature in the cabinet. I do not want to overheat my motor and ruin it. I make notes in my notebook of the various air temperatures at which I do all of this so that in the future I can duplicate these adjustments.

Here’s what my notes look like:

Outside air temperature: 30 degrees F

Bottom vent holes in cabinet open, lid on tight.

Black powder mill run

Start of mill run, cabinet temperature: 30 degrees F

10 minutes into run, mill temp: 57 degrees F

20 minutes into run, mill temp: 64 degrees F

30 minutes: 73 degrees

40 minutes: 81 degrees

50 minutes: 90 degrees

60 min.: 95 degrees

70 min.: 105 degrees

80 min.: 108 degrees

90 min.: 114 degrees

110 min.: 117 degrees

I then stopped the mill remotely and uncovered it. The inside of the cabinet felt warm. The thermometer remote sensor had been placed down near the motor which felt pretty warm to the touch, but not so much that I would be worried about it being damaged.

Upon opening the jar, the mill dust was still loose and lying around the media and the dust was looking very fine and well milled. The media was only mildly warm to the touch, I’d guess in the 80-90 degree F range.

Conclusion: On a cold winter day like today, the configuration of the mill and the vents worked well. It got nice and warm, though, so I’ll pay close attention to these readings on a hot summer day and adjust accordingly.

Keeping a notebook of info like this is very useful in the long run.

Of course, if one has a farm out in the country and can set up a tent or erect a shed to use for ball milling, and there is no danger of unsuspecting bystanders getting near it during milling, then the barricading may not be necessary.

Now, I can just hear some of you saying, “Jeez, all I want to do is make some homemade black powder and some stars and put a shell together and fire it. Do I really have to go to all this trouble? Aren’t you being a bit finicky and paranoid, Ned?”

This ball mill, and the cabinet, and the sandbags, and the buckets I’m about to show you, and especially the efforts put forth to do all of this the right way all amount to an investment in an art which can reap rewards for a lifetime. There really is no substitute for preparing to perform these tasks safely. And you’ll sleep better at night knowing you have done so. Do you want to hurt some little kid?

I have never had a mill explosion, and I do not know anyone who has. I have heard of them, though. All of this is cheap insurance just in case your next mill run is the one that explodes.

The jar is charged with media and material. The mill is set up and barricaded. The timer is set for the duration of the mill run. My thermometer is up and running. I plug my 100-foot extension cord into the mill, then go back to the house and plug that end in, and let ‘er rip.

Coming back after the amount of time set on the timer, when she’s stopped running, I uncover it all.

It’s time to dump the contents. But, the media and the material are all mixed together. How can I separate them? The fastest way is to use bucket screens. Here’s how you can make them.

Note: Even a cloud of charcoal dust can create an explosion if it is ignited. Do the following step outdoors away from sources of ignition, while wearing a good dust mask/respirator.

After a mill run, the mill jar is opened and the contents are carefully poured into the separation bucket screen, which is resting in the receiving bucket. After placing a lid loosely on the top of the separation bucket, with a swirling motion the material is easily separated from the media. The separation bucket is then removed, the lid is put onto the bottom bucket which has the milled material in it, and the media is poured back into the jar.

Keep the material covered by the bucket lid until it is transferred to a storage bucket and lid. If it is a completed black powder composition, always minimize the amount of time it is exposed to any possible source of ignition.

Rather than trying to pour the media directly from the separation bucket back into the jar, it’s easier to pour the media into a smaller, more pliable bucket. This smaller bucket’s mouth can then be bent into an oval for pouring the media back into the jar.

To keep from cracking the bottom of the PVC jar, tip the jar onto its edge, and pour the media back in slowly and carefully.

Practice good housekeeping and maintenance with your mill. Clean up any spills immediately, and lubricate bearings as necessary. Tighten screws, nuts and bolts occasionally, and check the whole rig for wear and tear regularly.

You should never be near the mill when it is turned on, or when it’s running, so there should be no danger of your shirt sleeve or ponytail getting caught in the moving rollers. Right? That is a directly driven drive shaft in there, so exercise appropriate caution around it.

So, we’ve covered ball milling, including:

• What purposes are served by milling.
• What can and cannot be milled.
• The mill base, jar, media, and material charge.
• A cabinet for the mill.
• Locating and barricading the mill and general mill safety.
• Monitoring the mill’s temperature during milling.
• Mill run times.
• A nice separation screen for separating the media from the material.

So, there ya have it. Ball Milling 101.

Until next time, happy and safe milling.

Stay Green,

Ned

How to Make Charcoal

This essay on making charcoal is a slightly revised and updated version of one which appeared in the Pyrotechnics Guild International (PGI) Bulletin #152 in 2007. It was the first of four articles that explained how to make two, nice 8″ aerial willow shells in 2 1/2 days, say at a weekend pyro club event.

We are going to reprint that four part series here in the Skylighter Newsletter over the next few editions, adding one more part to it which will explain Ball Milling 101.

In the summer of 2006, the BATFE (Bureau of Alcohol, Tobacco, Firearms and Explosives) was at the PGI convention gates asking if attendees were bringing shells onto the site and if so, where they had been made and how they had been stored.

The Consumer Product Safety Commission was pressuring the chemical suppliers to sell certain chemicals, in particular quantities, only to licensed manufacturers. Because of these pressures, many pyros are finding their shell manufacturing options limited.

Some folks have the ability to become licensed, quite a few local clubs are doing the same, or have licensed manufacturers in their ranks, and folks are being offered the opportunity to manufacture on-site at club get-togethers. For many of us, these guild events provide the only opportunities for shell manufacturing.

I’d like to present some ideas on ways to produce really excellent traditional paper ball shells, from scratch (stars, burst powder, shells, rising tail, and lift powder), in a minimal timeframe scaled to such an event. If one were to start this process on a Friday morning, these shells could be fired on Sunday evening, utilizing a 60 hour process, and with minimal chemical requirements.

A fireworker could provide a few basic tools of their own, such as a ball mill, and share other equipment, for example a hydraulic press and star/comet plates, with other people. They could travel to the event and enter the gates with no complete pyrotechnic compositions whatever.

The one custom chemical ingredient that I think really optimizes this project is homemade charcoal, which should be made prior to the event. If someone were to ask me what I think the most basic pyro skill is, I’d answer, “Making good charcoal.”

To me, there’s something most satisfying and almost magical about making this very basic pyrotechnic component from scratch. It’s like a painter making their own paint from pigments found in the earth. Watching raw wood transformed into nice homemade charcoal over a period of a couple of hours brings us back to the basics of this art.

On the various pyro discussion lists, one of the most often-heard conversations is about Charcoal. Many are searching for the Holy Grail of charcoals: That charcoal which will produce the fastest Black Powder, or the best sparks coming out of their stars and comets.

For fast BP, one will often hear folks tout the qualities of Willow wood charcoal, or Alder Buckthorne, or Aspen, or Balsa. For good sparks, I’ve heard various woods recommended: apple, peach, (I’m feelin’ hungry for some pie), pine root, pine, and others.

There is a really excellent article on making charcoal on the Passfire website, a resource I highly recommend for all of its informative articles. In that essay, the author discusses various woods that can be used in making charcoal, and settles on spruce/pine/fir (SPF) wood such as 2×4 scraps from house framing and the like. Sometimes this wood is referred to as whitewood. It is a softwood (conifer), as opposed to a hardwood (deciduous).

The advantage of these species is that the charcoal made from them can be used to make high quality Black Powder for lift and burst, and can also be used in charcoal stars where it produces nice, long-lasting spark trails. It’s also a cheap, readily available wood. (In the Midwest, US, where I live, all of our ‘white wood’ framing lumber is either spruce or pine, so I can’t claim to have any experience with using fir, which may be available out West. Yellow pine, which is used around here for 2×8,10, and12 framing lumber is not the same as the white wood spruce/pine. I don’t think its charcoal is useful for us.)

I refer to the type of charcoal available here at Skylighter as Commercial Charcoal. My understanding is that this charcoal is made from mixed hardwoods: oak, ash, maple, and the like. (For years there was a rumor goin’ round that it was made from coconut shells, but that was just an urban myth.)

I guess the charcoal is made at some factory which is geared to making large quantities of generic charcoal for various purposes. I’d love to see that operation some time, and the resulting mess that must accompany such production. Believe me, if you saw my face and clothing after I’ve been making and grinding charcoal, you’d know what I mean.

Commercial Charcoal can indeed be used to make perfectly serviceable Black Powder, stars, comets, and rockets. It may not make BP that is quite as powerful as that made with some of the homemade “designer” charcoals, but if a bit more of the BP is used it will work fine. It takes a bit of experimentation and testing to determine the final quantity to be used, and therein lies much of the pyro-fun for many of us.

After much of this R&D, when making homemade charcoal, I’ve determined that the SPF-whitewood suits my needs just fine for both black powder and sparks.

Making charcoal is a simple, basic process which can be carried out at most homes and neighborhoods on a small scale. Even airfloat charcoal can be produced with the use of a ball mill. Large scale production is probably best done out in the country because there is a lot of smoke produced when cooking large quantities of wood. To cook charcoal, one simply needs some wood to cook, a fire, and a retort.

We’ve already decided what wood we want to turn into charcoal.

A fire, such as that in a backyard fire pit, fireplace, or chiminea (one of those little pot-bellied stoves that many folks have out on their decks) is necessary.

I’d like to emphasize that, when I’m cooking charcoal in my fireplace as illustrated in some of these photos, I only cook loose, split whitewood, and I keep the wood a good half inch down from the lid. I don’t want the wood to block the vent hole and cause pressure to build up in the retort. In general I prefer to cook charcoal over a fire outdoors because I think that is the safer practice. The last thing I want is a retort popping open and sending burning wood into my family room.

The vessel that the wood is heated in is called the retort, and it is the other major component of the process. In my fireplace, for a retort, I use a stainless steel stock pot with a stainless lid that I got from my grocery store. I have used this pot for numerous cookings, with no noticeable degradation of its quality other than a bit of warping of its bottom.

In my chiminea, I use a new, empty, one gallon paint can that I bought at Home Depot. Or, if I want to cook a small 2-3 ounce experimental batch of homemade charcoal, I’ll use a new quart can. I call that one the “quart retort.” A new paint can will only cook 3-4 batches before the bottom begins to disintegrate. (Stop using it before this happens to prevent getting metal debris in your charcoal, which could cause sparks when ball milling the charcoal as a component of black powder compositions.)

To fill the large, stainless steel pot, I take 2×4 SPF wood scraps, cut them to the appropriate length, and split them into pieces about 3/4″ square using a glove, an axe, and a log to split on. As I mentioned above, I like to cut the wood about a half inch shorter than the inside height of the retort.

I have found that the splitting works best for me when I place the axe on the end of the 2×4, lift both of them together, and then let them fall onto the splitting log. I’ve kept all my fingers with this method.

Then I fill my retort with the split wood, keeping the wood about a half inch short of where the bottom of the lid will be.

To fill the quart retort, I bought a piece of pine 1×4, which was almost free of knots, from the Depot. Knots are much harder than the rest of the wood and, in general, it is best to eliminate as many of them as possible when cooking the wood into charcoal.

Now I secure the lid of the stock pot with little C-clamps purchased at Home Depot. (I know, I know, Home Depot sees a lot of me.) There is a hole that I punched in the lid about 3/8″ in diameter. If I am using the paint can, I simply install the lid securely after punching a quarter inch hole in the center of it with an awl. I don’t use a drill on the lid, once again to avoid introducing metal shavings into the charcoal.

Since these photos were taken, the little aluminum rivets that held the side and top handles onto the stock pot melted during cooking, and the handles fell off. I had to enlarge the holes in the handles and the pot, and re-secure them with steel bolts. After doing the necessary drilling, I was very sure to wash off all the metal bits that resulted, so that they didn’t contaminate my charcoal and cause a future problem during milling.

After filling the retort, or before I start filling it, I build a good fire in my fire location. Then I put the pot in the middle of it, building the fire up around the sides of the pot and keeping the fire burning well by adding firewood as necessary.

In a few minutes smoke and steam will start to vent out of the hole in the lid, increasing until there is a quite noisy plume coming out of the hole. One of the advantages of doing this in a fireplace, as opposed to doing it on a hot plate or gas burner, is that the flames consume the smoke and steam coming out of the retort, which otherwise, can be quite smelly and a potential bother for neighbors.

After a half hour or so, the white emission starts to become transparent and will catch fire, forming a little blowtorch emanating from the lid until the wood in the retort is done cooking.

For the scientifically minded, this info is from Wikipedia:

Charcoal is the blackish residue consisting of impure carbon obtained by removing water and other volatile constituents from animal and vegetation substances. Charcoal is usually produced by heating wood, sugar, bone char, or others substances in the absence of oxygen (see char). The soft, brittle, lightweight, black, porous material resembles coal and is 85% to 98% carbon with the remainder consisting of volatile chemicals and ash.

I guess the initial smoky steam column is mostly water being driven off, and when the column becomes transparent and catches fire, the ‘volatile constituents’ are being forced out, leaving only the mostly carbon remains.

The paint pot usually takes about 1 to 1 1/2 hours to cook, while the stock pot takes 2 – 2 1/2 hours. The charcoal is done when the flaming gasses stop coming out of the lid of the retort. At that time the retort is removed from the fire and allowed to cool, usually overnight.

Some folks plug the vent hole in the retort lid with a stick, or cover it with a coin while the contents cool, to keep them from igniting and burning down to ash, since oxygen is being allowed in during cooling. I have not found this to be necessary, but I always keep the possibility in the back of my mind.

After cooling, the lid and charcoal are removed from the retort. The charcoal can be broken up and smashed into small pieces by putting a small amount of it at a time into a 5 gallon plastic bucket and crushing it with a three foot length of 4×4 lumber.

This is a messy operation, to be done outdoors, with the wind blowing the dust away from you. And, I always wear a good respirator/dust-mask while doing it so that I don’t breathe all that nasty dust.

The crushed charcoal is poured from the large bucket into the small bucket, and the top of that bucket can be pinched into an oval for careful pouring of the contents into a ball mill jar for milling into airfloat charcoal. (More on ball milling in the next article.)

Or, if one needed some other mesh size of charcoal, say 80 mesh, the mashed charcoal could be screened through various sized screens to separate out the desired particle size.

Another option for smashing the cooked charcoal is shown in the photo below. This works very well for small quantities of charcoal. The corner of the square pan comes in handy when it comes time to pour its contents into the mill jar. (I did not let my wife see me using this kitchenware for this purpose. Please don’t tell her about it.)

When I used the grinder for the first time, I ran some charcoal through it to remove any metal shavings or debris from the grinder, and I threw that charcoal away. I can’t emphasize enough how important it is to me to keep any debris, which might cause sparks in the milling operation, out of my charcoal. I’ve heard of folks putting their homemade charcoal in doubled plastic baggies and running over it with their car in the driveway to smash it up. All I can imagine is little bits of sand, dirt and gravel getting into the charcoal, which would be a bad thing.

I then ball mill the pieces for a couple of hours until airfloat charcoal is produced.

The stock pot yields about 3 pounds of charcoal and the paint can produces about a half pound, while the quart retort yields about 2 1/2 ounces.

The end result of this process is quality charcoal that is very useful in producing powerful black powder or charcoal streamer stars.

The next article in this series will describe a ball mill and the efficient ball milling of charcoal, individual chemicals, and black powder compositions.

Stay tuned and Stay Green.

Ned