1-1/2″ Vise Screw Drilling Jig

During the Hand Tool Woodworking workshop one of the things that gave some folks trouble was drilling the 1-3/8″ holes in the aprons for the twin 1-1/2″ screws that would be installed once the holes were tapped.  At issue was getting the holes not only in the correct place, which was not much of a problem, but drilling them parallel to each other and exactly perpendicular to the apron.  There is an art, or a least a practiced technique, to drilling clean holes with a large Forstner bit and a hand drill.

I decided to try building a jig that could suffice for the problem.  The challenge was that the 1-3/8″ cutting head was affixed to a 5/8″ shaft.  My jig design reflected that reality.  I set a piece of scrap 3/4″ plywood on a pair of feet to make sure there was room for the drill bit cutting head to fit and also a place for any chips to go.  The first thought was to drill a 5/8″ hole and just feed the bit shaft through it from beneath, but on second thought I drilled and 7/8″ hole to hold a 5/8″ I.D. bronze sleeve bushing.  The bushing was roughed up on the outside and tapped into the hole slathered with Devcon epoxy.

The limitation of the system is that the hole can only be as deep as the shaft protrudes above the jig plate.  Given that most of the time I’m hand drilling through two layers of 2x stock on the front apron the depth of the hole from using the drilling jig is deep enough (and straight) that completing it free-hand is adequate to accomplish parallel holes fully through the apron.