Building Fittings
Jump Run Enterprises, LLC

4130 Steel Tube Airframe Construction Video
Building Fittings:  "You will probably need to build several fittings and control horns from flat stock.  To make fittings, first make a flat pattern using poster board, or manila file envelopes."
"Then cut the pattern out, tape it to the flat steel, and use a fine tipped black sharpie pen to draw the outline on the steel."

"Make sure to take into account the grain of the metal when setting your pattern on the steel" 

The Step Drill:  "Another great tool to have is a Step drill.  Good ones are fairly expensive, at up to $22 each, but they are well worth the money.  They also come in about 3 size ranges."

"I will usually mark the diameter I need to drill to with a piece of tape so I know when to stop drilling."