Fig. A: Put a ¼"-diameter transfer punch down each
hole you are duplicating, and tap with a hammer.
FIg. B: Before using the desired-size drill bit, minimize
wandering by making a preliminary pilot hole using the
smallest-diameter bit possible. Fig. C: Drill intermediate-sized holes, working up until you get to the size hole
you want. It’s a perfect match!
no cutting; it forces the base material out of the way drill a few intermediate-sized holes, each serving
so the bit can advance through the plate. as a pilot to guide the drilling of the next, until you
The force of pushing this projected cylinder of finally get to the size hole that you want (Figure C).
material out of the way has the potential to make Use the web diameter to select your size sequence.
the bit wander by up to ¼ of the diameter of the When the final hole diameter is critical, use a drill
bit — depending on how perpendicularly you’re bit that’s 1 size smaller than the final hole size you
pushing the bit in, how rigidly held your work piece want, and carefully clean the hole out with the final
is, and how sharp the 2 cutting edges of the bit are, size drill bit.
relative to each other. If the position of the hole is Always use a sharp bit. Dull bits will wander
critical, as it is in our example, you want to make a and make sloppy holes. The bit’s sharpness can
preliminary pilot hole using the smallest-diameter be determined by feeling the edges, and by visual
bit possible, to minimize the wander (Figure B). inspection.
The diameter of the pilot drill bit you select will be a
tradeoff between how badly you don’t want to break Mose O’Griffin is a prototyping engineer with 18 years of
off a tiny drill bit in your part and how accurate you machine shop and fabrication experience.
need your hole pattern to be. (A smaller-diameter bit
must spin very fast, and is much easier to break.)
The more skilled you become, the easier it will be
to drill a hole in a ½" plate with a #60 drill bit. Typically I reach for a #43 bit, because it’s neither too
big nor too fragile for most jobs, but I have certainly
drilled my share of #60 holes when I need a tiny and
Photography by Mose O’Griffin
4. Drill the full-sized hole.
If you’re making a very large hole, you may want to
I keep a roll of cheap stretch wrap around
the shop. It’s great for packing away tools
that aren’t likely to see use any time soon. A
quick spray of WD- 40 and a cocoon of plastic
wrap keep tools and accessories free from
dust, rust, and abrasion. —Frank Joy
Find more tools-n-tips at makezine.com/tnt.
140 Make: Volume 15