Quarter-inch pilot bits in hole saws have a tendency to enlarge the pilot hole as they cut. The result is an egg-shaped hole because the pilot bit wanders. Fortunately, the solution is simple.
1. Cut a piece of 1/4-inch steel rod. Grind or file a flat where the set screw will land. The flat keeps the pilot from rotating in the cutter.
2. Cut a piece of plywood or hardwood. Drill a hole and enlarge it to 1/4 inch with a reamer. The reamer leaves a perfectly round hole to the correct dimension. The wood block serves as a sacrificial backing plate and guide.
3. Drill the guide hole in the part and ream to 1/4-inch diameter.
4. Secure the wood block to the drill press with the hole-cutter guide pin perfectly aligned in the guide hole. If possible, clamp the part to the guide block.
5. Double-check that the holes are aligned with the guide pin.
6. Lube the cutter and guide pin with a good lube like beeswax or Boelube stick.
7. Set the drill press for a slow speed: 250 rpm is a good.
8. Proceed with low pressure and be ready for the cutter to break through. It can hang on the last bit, so back off and take a look. Apply very little pressure as it breaks through, or pull the part and cut the last bit by hand with a Dremel and cutoff wheel.