For a long while when I first started into pyrotechnics I avoided rocketry. It was not that I found rockets less enjoyable to watch than other forms of pyrotechnics, I simply believed they required a large array of expensive tools and therefore passed them over because I was more interested in spending that money on chemicals for building big and impressive shells.
It took years of envying others who could build rockets and watching the soft lift into the sky before I realized that I preferred shells lifted in that manner to those that are blasted out of a mortar. That realization forced me to reconsider rocketry as something I would like to experiment with.
I was still unwilling to spend hundreds of dollars on commercially made tooling for something I wasn’t even sure if I would enjoy, so my only option was to make tooling myself. Black powder rockets are the safest type of rocket to make and use, and the simplest to perfect, so they proved to be the best type to start with. The tooling I designed and the method in which it is used can be seen demonstrated in the video below:
Now onto how to make the tooling...
Step 2: Making the Tooling
This tooling is made for rockets with an engine 4 1/2″ in length, and 3/4″ in internal diameter. With the aid of a bench grinder, a drill and a few grades of sandpaper, it turned out to be quite easy to shape a spindle out of a 3/8″ x 4 1/2″ threaded brass rod. With masking tape protecting the threads, the rod is chucked into the drill and spun at high speeds while in contact with the grinding wheel. This keeps the amount of material ground off the rod spread evenly around the circumference. A slight taper is given to the rod with the thickest part toward the threads that are chucked in the drill, and tapered down to about half the starting diameter at the tip. The thickest part at the bottom should be just narrow enough that all evidence of the threads is sanded down. To make the tooling exactly as shown in the video, the top 3″ of the 4 1/2″ rod are shaped, and the remaining 1 1/2″ is left threaded for the extractor nuts to thread onto.
The bench grinder provides a very course grind, leaving deep scratches in the spindle. Because of that, the spindle needs to be ground down slightly more after the wheel has done the bulk of the shaping (removing the threads, giving the taper). 100 grit sandpaper held against the spindle while the drill spins it does a good job of removing the deep scratches, and 4-600 grit will give a good polish to the metal. The smooth surface will reduce friction when removing it from a rammed rocket, and leave a solid and undisturbed powder core.
The spindle can now be finished off by placing two nuts onto the threads and tapping the threads on the bottom of the spindle gently to pinch them closed so the bottom nut cannot spin off. A washer is then dropped over the spindle to sit above the two nuts.
The base for the spindle is then formed with three squares of hardwood (oak) measuring 2 1/2″ x 2 1/2″ x 3/4″.
Two of the blocks are held together and a 3/8″ hole is drilled straight through both of them. The top block is then removed and the hole in the lower block is widened to 3/4″. All three blocks are now stacked on top of each other and clamped to prevent them from shifting – the block with the 3/8″ hole on top, the one with a 3/4″ hole in the middle, and the solid block on the bottom. Now on opposite corners of the stack a 1/8″ hole is drilled straight through to the bottom block. Through these two new holes a 3″ decking screw is driven in to the point that the threads are dug into the bottom two blocks, but the smooth portion of the screw towards the head is all that remains in the top block. There should be plenty of room that this can occur without sinking the head of the screw into the top block. The heads of the screws are then cut off with a hack saw so that the top block can be removed, leaving the bottom two blocks held together with the smooth shank of the screws sticking out of the two opposite corners. If the points of the screws are sticking out of the underside of the two blocks those points can now be removed so the tooling sits flat.
The top block of the tooling should now be able to be lined up with the two pins and snapped down onto the tooling aligned exactly the same way every time.
A small recess 1 1/4″ in diameter should now be drilled around the 3/8″ hole on the underside of the top block so that the washer on the spindle will be able to fit between the top and middle block when the spindle is inserted. That will complete the tooling base.
The threaded end of the spindle with the two nuts threaded onto it and the washer sitting on top is now inserted into the 3/4″ hole in the middle block of the base, and the tip of the spindle is threaded through the 3/8″ hole in the top block which is snapped in place.
3/4″ diameter dowels are then used to form the rammers. A drill press makes it a simple task to drill out the holes through the longest two rammers for the spindle to feed into. The following lengths of dowel should be used for the three rammers: 5″, 3 1/2″, & 2″.
As is shown in the video, the longest rammer needs the full 3″ length of the spindle drilled out, and the end tapered to form the nozzle. The 3 1/2″ rammer only needs a 2″ core, and the shortest should have no core. Even though the threaded rod that the spindle was made of started as 3/8″ diameter, after grinding it loses quite a bit of that material. Therefore the holes through the rammers can be made smaller than 3/8″ diameter, though how much smaller depends on how much of a grind and taper was given by the maker of the tooling.
Step 3: Black Powder Rocket Fuel
The term black powder can be used to describe any pyrotechnic composition composed of the three chemicals, potassium nitrate, charcoal, and sulfur. These three chemicals can be combined in a variety of ratios to fit specific purposes. The traditional mixture that would be used in black powder firearms and pyrotechnic purposes other than rocketry is a ratio of 75% potassium nitrate, 15% charcoal, 10% sulfur, all measured by weight and milled with lead media to make an intimately combined mixture.
This ratio typically burns far too quickly to be used as fuel in cored rockets, a more ideal ratio being 60% potassium nitrate, 30% charcoal, 10% sulfur. If all chemicals are finely powdered they need not be ball milled, and may simply be mixed together by screening. It is likely that this fuel will work fine in rockets made according to the above video. Should it burn too rapidly and cause the rockets to explode, additional charcoal may be added to slow the fuel. If the rockets do not take to the sky but instead burn out on the ground, it is possible that the fuel is burning too slowly, in which case the charcoal in the composition may be reduced. Increasing and reducing components in a composition can be a tricky process to get right if done too quickly, so when making changes do not add or remove more than 2% of a chemical at a time. This will allow you to dial in the ideal fuel. Be sure to take consistent and thorough notes so any changes that may cause a success or failure are recorded.