The Spencer Mk. I Nozzle was created using a a 3/8 inch steel plug, found at Home Depot. A drill press was used, incrementally changing bit sizes to roughly match the desired nozzle contours. A conical sanding Dremel bit was then used to smooth out the steps, forming our nozzle.
For the chamber a 19 mm O.D. steel conduit is used. One of the major safety factors is the seam weld, keeping the majority of the chamber from fragmenting in the event the chamber wall ruptures. A roughly 140mm length of tubing is cut and the interior of each end threaded.
A similar method to the nozzle is used for the cap housing the powder ejection charge. A small hole is drilled through the entirety of the plug, this smaller hole resting against the delay charge. On the other side a larger hole is drilled, housing the ejection charge. A small paper towel/toilet paper sheet is used to plug the powder. A 3D printed, single-use ejection cap was considered, but heat and reusability eliminated it.
Potassium Nitrate (KNO3) and Powdered Sugar (Sucrose) are mixed together in a pan of water, 65/35 O/F ratio. Sixty-five grams of KNO3 and thirty-five grams of sucrose are added to the water. Cooking continues with near-constant stirring until all water has boiled out. The propellant continues cooking until fully caramelized, and is then quickly cast into the motor chamber. Coating a roughly five millimeter core rod with WD-40 or something similar, the core hole is created. After a minute or two the coring rod is removed, the propellant left to cool. Once cooled the motor is ready for flight, all that’s left is the ignition source.
Using a pair of needle-nose pliers, a paper towel, and a Christmas tree lightbulb, an igniter is easily crafted. Wrap the bulb in the paper towel, then use the pliers to crush the tip of the bulb. With the filament now exposed to the air, an electrical current will cause it to burn up. Now add some gunpowder to the bulb. This will give the igniter significantly more flash and flame volume, leading to a higher chance of motor ignition. Connect the two leads to a 9-volt battery/18-volt drill battery.
6For those curious about the name: