Fairing Model: Tool Design
Dateline: 03/17/99Initial Concept
The main factor driving the design of the fairing tool was cost: it had to be as cheap as possible. Because only one part was needed, and the surface quality didn't have to be great, an expendable tooling approach was chosen.
The idea was basically to use a one-off foam construction technique. A large wooden frame would be built, covered with foam, and then machined and sanded to shape.
We planned to wind the part, so the tool was designed to fit on our filament winder. This basically meant the tool needed a central shaft to fit into the machine chuck and the tail stock. The filament winder can be fitted with a machine head (basically a router bit), so it could be used to machine the tool to final shape.
These requirements led to a simple design of a shaft with circular bulkheads. The bulkheads would be machined to the nominal inside part diameter, providing a template for machining the foam.
Final Concept
The main OSP design effort was taking up most of my time, so I handed off manufacturing of the model to one of our students. Rebecca Cohen had been working summers with us for several years and was ready to take on some big projects of her own. This one would require design and manufacturing skills as well as supervision (it was too big for one person to build alone).
Rebecca's first job was to turn my rough sketch into a real design. She started by calculating dimensions for the bulkheads (unfortunately, I'm not allowed to show those details) and selecting materials: half-inch, medium density particle board for the bulkheads; and a 3 inch gray cast iron pipe for the shaft. The latter choice would end up causing us lots of problems, but it's something I should have caught when I reviewed the design.
The only significant change to my original idea was the addition of support shelves for the foam. These were basically smaller diameter bulkheads, flush with the main bulkheads, which provided a more secure method for holding the foam in place.
After a trip to the local metal center for the iron pipe and Home Depot for particle board, screws, and Liquid Nails (for gluing the foam in place), we were ready to begin manufacturing. Next article, I'll start showing the actual construction.