Acid Baths for Etching Aluminum Mandrels


While the rotors are done, we need a structure to hold the whole assembly together. Parts of it will be made using tapered carbon tubes to maximize weight efficiency.

As we did with the rotors, we had to make from scratch a mandrel to cook the carbon in the proper shape. Since these members are much thinner we used an acid bath technique. In theory, if a section of tube is removed from an acid bath at a constant rate the tube will be thinner at the bottom and thicker at the top.

We rigged up a PVC pipe bath on the side of the farm with a length of rope used to lower and remove the aluminum rods that would form the mandrel. After a day of running back and forth on my part, the mandrels were tapered to the proper thickness. They then needed to be joined and polished so that carbon could be laid-up on top. To speed the process up we formed an assembly line using the whole team with increasing grits of sanding paper to polish the tube. Now that the tube is polished we're moving on to producing more carbon fiber tubes for the support structure.

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