I used to have the hardest time getting a clean exit hole when I was drilling through wood. A good set of lipped brad points, or the Wood Owl Ultra-Smooth Auger bits could almost get me there. But it seemed the only way to accomplish this goal with certainty was to drill through the part into a sacrificial board that was clamped to the exit side.
This presents a problem at the drill press. Your sacrificial board is supposed to be the table. So now you're changing the little square in the middle of the table every time you change bits. And even that doesn't guarantee a blow-out-free exit.
I got fed up with this a long time ago and took a page from Roy Underhill's book. Yes, those who refuse to put down their bits and braces in exchange for a modern cordless drill can still teach us a thing or two about better ways to use our tools. In this case, the idea is to stop short of exiting the hole and finish drilling from the other side. And while they're typically using auger bits, I do this with any good center spur bit. The process is simple.
Set your depth stop up so that only the center point of the bit exits through the work and pierces the table.
Drill the hole to the depth of the stop.
Flip the part and use the hole to center the bit.
Finish drilling.
No need to turn the drill press off or clamp the work to the table.
In eliminating the work of replacing backer boards or clamping parts to scrap, this method does add one extra step. The process leaves behind a small wooden slug. Sometimes it stays in the hole and sometimes it sticks to the end of the bit. It's pretty easy to knock the slug out of the hole. But if it sticks to the bit, and you're not the daring type who likes to touch the hot pointy end of a spinning drill bit, you'll need to stop the drill press and knock it off.
To see what the whole process looks like in real time, you can watch the short video below. My apologies for the poor quality video. And the drill press is a little loud... you may want to mute your audio.
My workbench students like to keep a few of these slugs as souvenirs. Once, I even caught a couple of them who had different accent woods trading walnut and cherry. I typically pop them out while standing over the scrap bin, but yesterday I found an unexpected use for them.
I'll talk about that next time.
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