Page 146 - Robot Builder's Bonanza

THE METALSMITH’S ART 115

Cutting sheet metal by hand is a chore, but it can be done with a bit of work. These are
some specialty hand tools for cutting sheet metal:
Aviation snips are suitable for aluminum under 1/8″ (0.125″) thick, or 18- gauge thickness
for steel. When cutting out circular bases, consider using a right- or left- hand tool; it’ll
make better cuts. “Right- hand” and “left- hand” in this case refer to the direction of the
cut, not whether you are right- or left- handed.
A nibbler tool takes out little bites to cut and shape the metal.
Pneumatic shears make quick work of cutting sheet metal. I don’t know what I’d do without
mine! The shears themselves are relatively inexpensive (most under $40), but you need a
suitable air compressor to power them. An alternative is all- electric sheet metal shears, but
these cost more. With both, the maximum practical thickness is 18- gauge steel.

The basic steps are the same whether you use snips, nibbler, or shears:

1. Use a scribe or construction pencil (anything that writes on metal) to mark the cut you
want to make.
2 Hold the metal sheet in one hand— use a work glove if you need to— and the cutting
tool in the other, or clamp the metal in a vise.
3. Cut along the marked path. If you need to make sharp turns, you may have to cut (or
nibble) away from the scrap portion of the work, then approach the path from another
angle.
4. Smooth the edges with a metal file or fine- grit sandpaper, as detailed later in this chapter.
Figure 11-6 shows an example of galvanized 20- gauge tie plate being cut with an air shear.
Tie plates are very inexpensive (this one cost under a dollar), and they’re commonly used in
home construction.

Cutting Thick Sheet Metal
For thicker stocks, specialized metalworking tools are needed. On large pieces, a metal brake
is used to make straight cuts. You probably don’t own one of these, but if you attend school,
ask the shop teacher if you can use the school’s for a few minutes.
Very thick steel (1/4″ or more) can be cut with a torch,
then ground down as needed with an electric grinder.
Obviously, this requires a cutting torch and the experi-
ence that goes with using it.

Cutting Thin Sheet Metal
On the other side of the spectrum, the thinner aluminum
stocks (1/32″ and under) can be cut to shape using avia-
tion snips (see above) or even a pair of heavy- duty scis-
sors. You can also use a scroll saw, as long as it is a
variable- speed model (use the slower speeds) and you’ve
equipped it with a metal cutting blade.

Figure 11-6 Air shears make quick work CUTTING A FRAME
out of cutting sheet metal. Use a pencil to mark
the line you want to cut, then slowly work the Robot frames can be constructed using aluminum
tool around the contours of the line. extrusions, described above in “Metal from Your Home

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