Page 205 - Build Your Own Combat Robot

Build Your Own Combat Robot
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or extruded?”—and a host of other questions. Extruded geometries include an-
gle-shaped bars, tee-shaped bars, I-beams, C-channels, and square and rectangu-
lar tubing.
You can choose from among at least nine common aluminum alloys: 1100,
2011, 2017, 2024, 3003, 5052, 6061, 6063, and 7075. If that list makes your
head spin, add to that numerous tempers for each of the alloys. Don’t despair, for
even though each of these alloys has an application where it fits best, we’ll discuss
only the few that seem to be best for robots—considering just how well you can
machine it, its cost, and its availability.
Alloy 6061 at a temper of T6 seems to be one of the most versatile and readily
available aluminum types for sheet stock. This popular aluminum alloy comes in
sheets from 1/32 inch (0.032 inch) to several inches in thickness (the thicker ver-
sion is called plate rather than sheet) and can be up to 48-by-144 inches in size.
This alloy is available at aerospace surplus yards, metal supply houses, and the
better specialty hardware stores, and it is fairly good for robot skin covering and
excellent for internal structures. It welds, drills, and taps well. Alloy 6061 also comes
in extruded angle stock, which is useful for fastening two pieces of sheet stock
together at right angles for structures. Alloy 6063 is similar to 6061, yet it offers
better corrosion resistance for wet applications.
Alloy 7075 is one of the hardest aluminum alloys and is an ideal material for
machining high-stress parts. It is popular in aircraft and aerospace production. It
also comes in sheet stock tempered at T6 and makes good robot skin. 7075 can be
found at most metal houses and aerospace surplus yards.
Alloy 2024 is another “aircraft-grade alloy that offers high strength and is
fairly machinable. 2024-T3 (T3 is a temper number) comes in extruded stock such
as rounds and squares. Alloy 2011 is also easy to machine and comes in rounds
and hexagonal stock. It is probably the best for threading and machining on a
lathe and milling machine. Robot hubs, shafts, and similar items can be easily
made from this alloy.
Aluminum alloys are easy to mill, cut, and drill, but the careful application of
cutting fluid to these operations will greatly assist your machining operations.
Thisisespeciallyimportantintappingaluminum.Tappingfluidsusedfordrillingand
tapping of steels should not be used. AlumiTap and special compounds designed for
aluminum should be the only types used. This also applies to cutting large holes
with a fly cutter or in sawing with a band saw. As always, use a good pair of goggles
or a face-mask when machining any material.
Aluminum, as well as stainless steel, requires special talents and equipment
to weld properly. Both require what are commonly referred to as wirefeed weld-
ers, also called MIG (metal inert gas) welders, or TIG (tungsten inert gas) welders.
You might have seen cheaper varieties of these types of welders in cut-rate tool
catalogs or stores. This is an area where more money means a better job, and cut-
ting corners just to own a MIG welder will cost you in the end with poor and weak
welds. If you want to save money, go to a welding shop that specializes in alumi-
num and stainless steel welding and have a professional do it right the first time.