Workbench Joinery: Drilling & Driving Screws
Aug 19th, 2011 by Andy
Most of the problems related to driving screws while building a workbench have nothing to do with the screw itself, but everything to do with the pilot hole (or lack of). I know it’s easy to assume pine is soft enough that you can simply force a wood screw to go where you want it to go. Sometimes this works, sometimes not. Overall, you can expect that most wood screws are too large to be forced into a board without some type of path to lead the way. Although they’re tempting to ignore, pilot holes can mean the difference between project success—or project disaster.
What Size Pilot Hole Should I Drill?
As a general rule, a pilot hole should be the same diameter as the root of the screw—the area just below the threads. This allows the bulk of the screw to easily enter a board without splitting the grain, while the threads do all the work of pulling two boards together to form a joint.
Countersink Bits for a Better Fit
A simple pilot hole might be fine for the threaded portion of the screw, but it won’t provide any space for the head or the shank. The solution is to use a countersink bit, which creates both a pilot hole for the threads, and a larger hole for the head and shank.
Tapered or Straight?
Some screws have a shank that is wider than the threaded portion of the screw. That’s when I like to use a tapered countersink to get the best fit. For screws that have a more narrow shank, I like to use a straight countersink bit.
Something else worth mentioning — the importance of using the torque adjustment control on a drill to drive screws. This can tell you right away whether you have a pilot hole that’s too small — and without destroying the head of the woodscrew in the process.