Sport Rocketry

SPORT ROCKETRY MAY/JUNE 2024 31 tom, I went very slowly and tried to an- ticipate any dangerous jarring jumps from the router. is technique is a pleasure for working with thin aluminum sheet. You can cut almost any shape, if you can first make a smooth pattern in a piece of wood or other stable material. e catch is that you have to smoothly rest your router on the aluminum sheet you are cutting. is might make for creative clamping to keep everything flush to the metal. In this case, it meant cutting the wood pattern block to the exact width of the aluminum sheet, so they both could be held together in the woodworking vise, with nothing sticking up to block the movement of the router. I used my full-scale CAD drawing to mark erous technical support of Chuck Penson, a fellow Titan II enthusiast, I have created a magnificent model rocket launch control- ler, with a few actual vintage parts similar to those seen on the control panel of each Titan II launch complex. e case came to me almost ready to go. It is a purpose-built small metal enclosure, designed for electrical projects. It is made of only two pieces. e sides and bottom are a bent piece of steel, and the front, top and back are made of a single piece of alu- minum. I added a carry handle to the front, and a similar structure to the back, also made from a large stainless steel drawer pull. e one on the back provides a place to wrap the firing leads, keeping them tidy when storing the unit. e ends of the leads are attached to a quarter-inch headphone jack, allowing them to rotate without bind- ing, and allowing me to change them out more easily than if they were hard-wired to the circuitry inside. I had to cut a few holes in the aluminum to make way for the battery holders in the back, as well as the illuminated callouts and the two key switches. e rectangular holes for the callouts and switches were cut with a Dremel and cleaned up and brought out to their final size and shape by hand filing. e round holes in the back where the battery holders mount were cut using a re- ally niy technique I've learned. Into a sol- id piece of wood I drilled large round holes that exactly matched the size and location of those to be placed in the aluminum. I then drilled a smaller hole through the alu- minum, inside each of the four locations where the larger holes would be placed. is smaller hole was large enough to al- low a carbide edged flush trim router bit to pass into. Clamping the aluminum tightly to the wood allowed me to run the router around in an increasing spiral, approach- ing the outside of the hole defined by each hole in the wood. When I got all the way out to the edge of the hole, the bearing on the router bit guided my hands around in a perfect circle, exactly matching the hole in the wood. e result is a beautifully clean machined hole in the aluminum, far better than drilling or any other method. Setting up on a milling machine and using an end mill or a boring bar would take a lot of time and effort to get right. See Figure 4. is technique followed a little practice I got with another project, where I cut simi- lar holes in the aluminum sheet that forms the floor of a fuel tank. I had read online where guys were saying that modern car- bide router bits can cut aluminum just fine. I must say, my first try in the fuel tank bot- the hole locations with precision, which can be seen in Figure 4. e holes contain four battery holders, each of which holds two D-cells. ese eight batteries are wired in a way that al- lows three volts to be used to power the lights and alarm buzzer, and to perform a continuity check. is check ensures that electrical connections are intact by send- ing three volts down through the firing leads and right through the igniter, but with insufficient current to heat the igniter. When both keys are turned all the way over against their springs, the other bank of bat- teries with 9 volts is unleashed on the ignit- er, which instantly lights the fire. e burn- ing out of the igniter, a normal part of the Figure 2. Figure 3.

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