The Fine Art of Metal Shaping II
by Bob Whittier
from Experimenter Magazine, April 1999
Anyone who has messed around with airplanes has, from time to time, wondered how such intricately curved
things as engine cowlings, wheel pants and wing root fairings might have been formed out of flat sheet
aluminum. Common sense says that the graceful compound curves to be seen in them could hardly have been
achieved by a sheet metal shop doing heating and ventilating ductwork.
The wheel pants often installed on volume-produced light planes are made by fastening together right and left
halves made of aluminum formed to shape by matching dies installed in a type of machine called a drop
press. Engine nose cowlings are also formed in such machines. A fixed die is attached to its base plate,
and a matching one to a weight that slides up and down in guide tracks. When this die is allowed to drop,
its weight whams the sheet aluminum into the desired shape. For the benefit of readers who want to learn
more about drop presses and dies, the best coverage of the subject we know is Chapter X (10) in
Aircraft Sheet Metal Work
by C. A. LeMaster, published in 1944 by American Technical Society, Chicago.
Aluminum shaping demonstrations given at aviation conventions such as EAA Oshkosh AirVenture by Kent White
attract much attention. At right he coaches a visitor in aluminum welding technique. Obtaining good
results from a torch requires knowledge. Tip size must be appropriate for work being done. Gas
pressure must be suitable for whatever tip is being used. Adjustment of flame is important; the
flame's sound is almost inaudible and just very soft when gas feed is well adjusted. Too much gas
pressure produces a ``hard" flame that easily presses on and blows out molten puddles. Flame
will also tend to jump away from the tip.
See Torches available from TM Technologies
But what about the compound-curved sheet metal parts on typical antique and custom-built airplanes? To most
aviation enthusiasts, how they are made is as big a mystery as is what goes on in the mind of a cow
blissfully standing in a pasture.
Well, last month we introduced you to Kent White of northern California and his wizardry at hand-forming
sheet aluminum. We also described the specialized tools he and others in this field use.
Present-day methods of forming sheet metal into intricate shapes are the result of centuries of experience.
In museums we can see handsome metal objects that were made hundreds and even thousands of years ago.
Consider, for example, the fine swords and intricate suits of armor used by ancient warriors. Such things
were made using hand tools and looking at them gives us great respect for the people of long ago. By the
time aviation arrived on the scene, metalworking techniques were well advanced.
When heated, aluminum turns from a solid to a liquid rather suddenly. If welding is done ineptly, the work
will be full of holes where gobs of molten metal dropped out. To do heating under best possible
control, Kent White prefers the lightweight
Meco Midget torch
shown at left. Top right - This marking pen makes black lines on aluminum that will stay on the work while
it is being processed, yet which will wipe off easily and cleanly with a cloth wet with thinner.
TM2OOO aluminum welding goggles
, lower center, are fitted with a special glass that gives a combination of excellent visibility with a high
degree of eye protection. Lower right - These inexpensive jersey work gloves slide over aluminum
surfaces in such a way as to make imperfections noticeably easier to feel than when the surface
is wiped with the bare palm.