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DRILLING HOLES IN THINGS 61

only a small handful of them regularly and the rest only very occasionally. That’s how it is
with me.
I use these five drill bits for the vast majority of the holes I drill for my desktop robots. I keep
them in a large block of wood for quick access.

Bit Size For Drilling:

5/64″ Starter or pilot holes
1/8″ Holes for 4-40 size screws
9/64″ Holes for 6-32 size screws
3/16″ Holes for 8-32 size screws
1/4″ Odds and ends (e.g., holes for feeding wires through)

Refer to Chapter 5, “Building Robot Bodies— the Basics,” for a summary of drill bit types,
FYI
including special coatings that are used to make the bits last longer.

• When drilling into metal or hard plastic (acrylic, polycarbonate), first use the 5/64″ bit to
make a pilot hole. Then mount the bit for the hole size you want.
• Unless you’re making really large holes, when drilling into wood and soft plastic (PVC or
ABS) you can go directly to the bit for the hole size you need.
• When drilling holes larger than 1/4″—and especially when working with metal— start with
a smaller bit and work your way up. For example, if drilling a 3/8″ hole, begin with a 1/8″
pilot, then switch to 1/4″, and finish with the 3/8″ bit.

SELECTING THE PROPER SPEED
Different materials require different speeds for drilling. High- speed drilling is fine for wood but
leads to dull bits when used with metal and cracks when used with plastic.

Material Drilling Speed

Softwood (pine) High
Hardwood (birch) Medium to high
Soft plastic Medium
Hard plastic Slow to medium
Metal (aluminum) Slow
Metal (steel) Very slow

Most drill motors lack a means to directly measure the speed of the tool, so you just have
to guess at what’s high, medium, or slow. Go by the sound of the tool. If you’re using a por-
table variable- speed drill, pull the trigger all the way in for full speed. Then let it out and esti-
mate half (medium) and quarter (slow) speeds by listening to the sound of the motor.

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