For years I have used a try-square or machinist's square to check that the drill bit and the drill press table were perpendicular. That has worked pretty well, but I have noticed that often my cars axles are enough out-of-line that additional axle alignment is necessary.
Drill Press tables (the flat work area that holds parts to be drilled) is usually mounted so that it can be rotated. Sometimes, it has a scale on the side showing degrees of tilt. Less expensive drill presses are likely to have less accurate markings. I found that the "perpendicular" markings on my drill press were about a degree off! That is fine for drilling holes in bird houses, but not so fine for drilling Pinewood Derby Axle holes!
A couple nights ago, I stumbled upon an alternative method that cuts the error in half and led to a quick adjustment of my drill press table. At the same time, it proves (or disproves) the orientation quality of the drilled holes. Here are the steps:
1. Lock the fence across the drill press table (approximately perpendicular to the table's axis of rotation.)
2. Drill left-side holes in two separate "car bodies", carefully assuring that the opposite side was firmly against the drill press table and the bottom of the car body was firmly against the fence.
3. Insert spare #44 bits in the drilled holes, leaving 2/3 to 3/4 of the drill bits' lengths exposed.
4. Slide the car bodies against each other with the right side against a good plane surface (e.g. drill press table) so that the exposed drill bits appear side-by-side as viewed from the top of the car bodies.
5. Observe whether the space between the drill bits disappears "all at once" or "gradually moving up or down." Holes from quality drilling technique will exhibit the "disappear all at once" behavior. If not, Stop the Test NOW.
The reason to stop now is that the drilling technique in not adequate to produce satisfactory hole quality. Some things you might do to improve technique are
Use a stiffer bit,
Expose less bit from the chuck,
Drill more slowly, and
Choose wood with better grain.
6. Turn one of the car bodies end-for-end (car bodies top-to-top or bottom-to-bottom) and again slide them until the exposed drill bits appear nearly side-by-side.
7. Observe whether the space between the drill bits disappears "all at once" or "gradually moving up or down." Holes from quality drilling technique when the table is perpendicular to the drill bit will exhibit the "disappears all at once" behavior.
Why does this help? Because the drill bits' deviation from perpendicular happens on both sides of perpendicular, and the angle between the two drill bits is twice the deviation from perpendicular.
2/19/2009 New! 3/1/2009 FIxed pic for step 6.
Copyright 2009 © by Stan Pope. All rights reserved.