Page 95 - Robot Builder's Bonanza

64 MECHANICAL CONSTRUCTION TECHNIQUES

Wood Plastic Metal
General Wood is readily drilled For soft plastics (like PVC), Metals should be drilled
using a motorized drill, speed settings same or using a motorized drill.
either handheld or drill slightly slower, as for wood. Small parts are more
press. Speed depends on For harder plastics (acrylic, readily drilled using a
the size of the bit and the polycarbonate), reduce drill drill press.
density of the wood. speed by 50 percent. Following are general
Following are general speed recommendations
speed recommendations. for aluminum and other
• Larger than 1/8″: 2000 soft metals. For harder
• 1/8″ to 1/16″: 4500 metals, reduce speed by
• Smaller than 1/16″: 6000 50 to 70 percent.
• Larger than 1/8″: 500
• 1/8″ to 1/16″: 1000
• Smaller than 1/16″: 1500
Bits Wood bits should be Use wood bits for soft For aluminum and other
ground to 118° (pretty plastics. For hard plastics, soft metals, bits should be
much the standard). For use a pointed bit designed ground to 118°, the
cutting all but very dense for acrylic and standard. For harder
hardwoods (e.g., oak), polycarbonate. metals like steel (and even
regular carbon twist drills hard plastic), use 135°
are adequate. bits.
For longer life, consider
titanium- and cobalt-
coated bits.
Cooling Air cooling is sufficient. If Air cooling is sufficient, but Use cutting oil for metal
the wood is very hard and if plastic remelts into the (thin aluminum can
thick, pause every hole, slow down the bit, usually be drilled without
30 seconds to allow the bit drill smaller pilot holes first, oil). The idea is to avoid
to cool down. or splash on some drops of excessive heat, which
water. dulls the bit.

Cutting Things to Size

Wood, metal, and plastic can be cut using hand- operated or power tools. For all but the light-
est materials, however, you will find that power tools make short work of the job.
In the realm of hand tools, practical choices are:

For wood, a backsaw; for metal and plastic, a standard hacksaw. The hack-
saw uses a replaceable blade, which is required when working with harder
materials.

A coping saw allows you cut tight- radius corners in wood, plastic, and softer
metals. A coping saw is similar to the hacksaw, except the blades are smaller.
Replace the blade when it’s dull.

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