by Bob Punch, March 2010
I am fascinated with the "Metal Spinning" operation that I recently witnessed and hope you will be too. Here's a small example of a process that can lead to some rather large end products, such as engine cowlings for airplanes. How many places do you know that manufacture and sell engine cowlings for Sopwiths, Neuports, Ryans, Wacos, or your own design?
This round "blank" below is a piece of aluminum 5 inches in diameter and less than a 1/16th inch thick. After being "massaged" in a lathe for two minutes by a craftsman, it became the cup you see to the right, with the sharp edge of the blank neatly rolled over, down, and under, out of sight or touch. All accomplished using one stout blunt ended hand tool that applied constant pressure towards the "mold" of the finished product.
These objects can be made one of several ways. If enough of them are going to be produced and mass production is economical, an expensive mold is created so that blanks can be stamped around the molds. Molds, however, can be in the $30,000 price range (and wear out) so "hand spinning" quickly becomes a viable cost saving factor.
In the next shots you'll see Larry, with a blank inserted into his lathe next to the mold, start it spinning, lubricate it with a grease stick, and then start his magic. On the right side of the spinning blank is the mold that he is going to replicate and as he applies considerable shaping pressure from his side, the blank starts to reshape itself around the mold.
In this last shot, you can see how Larry has expertly caused that two handed tool to roll over the sharp lip at the top of the cup into a very smooth edge, that's actually now hidden.
Now graduate from the small to the not so small - an airplane cowling. Consider wrestling one of those 200 to 300 pound laminated wooden cowling block forms below onto a 100 inch swing lathe, loading a suitable blank, and forming a cowl.