Monday, July 13, 2009
Drilling on Target
I mentioned some techniques that we developed and used while at North Bennet Street, and this isn't one of them...but it should have been. Any one who has ever made a chair or even more so, taught chairmaking, can tell you that drilling the crest so that the mortises line up with the spindles can be a trying experience. I have a method for teaching the technique using a target on the floor. A student at North Bennet asked me "why don't we use the target technique in the actual drilling" and I rambled something about drill alignment and went about my way. When I returned home, I started thinking about resolving the drill end of things and came up with this.
This is nothing more than a small rod stuck in the back of a disk that I epoxied on the back of my drill. The critical factor here is that the rod and disk are perfectly aligned with the drill bit so that when you look down the rod, you are essentially sighting down the bit.
When looking down the rod, if you can see anything but black (meaning the side of the rod), you are not sighting correctly.
Below is the view of sighting down the rod correctly.
To align with the target (which would usually be set around a hole for the spindles into the seat), the body of the drill should be on center of the target and the back of the drill should read all black. Here is a misalignment. Yes, the drill is centered, but the rod isn't. (The notches in the target are to make room for the stiles on the outer holes)
Here, the you are looking directly down the rod, but the drill isn't on target.
Here is the view that shows the drill in correct alignment.
Perhaps the only tough part of using this technique is getting used to moving your head with the drill to keep the rod centered. I taught Jeff Lefkowitz the technique by asking him to split it into two steps. One, center the rod by moving your head, Two move the drill into the center of the target while moving your head as well to keep the rod centered. With this he was able to do a great job.
Jeff's chair had an added layer of complexity that also made the use of this method more essential. The curved spindles in his chair didn't aim directly at the holes in the seat, so his first step was to offset the target from the holes a certain amount and then drill away as usual. I'm pleased with the results and plan to keep working with the technique. I'll show Jeff's chair in the next posting.