When I make legs,usually the last step is drilling the holes that will act as mortises for the pegs used to secure mortise and tenons joints. These hole passes through a mortise creating the possibility of tear-out as the drill bit both enters and exits the mortise.

Nice crisp edges!

At first thought, this doesn’t seem like a big deal; there will be a tenon hiding the tear-out and no one will see it. However, if the tear-out is too great it can lead to a loosely fitting peg that may eventually allow the joint to move, let the joint open, exposing an unsightly gap, or later become loose. An easy way to avoid this problem is to use a backer-tenon when drilling the holes.

A backer-tenon is simply a piece of scrap wood, sized and milled for easy insertion and removal that functions as a traditional backer-board. I make it slightly thinner in thickness (by a few thousands of an inch) than the mortise width and a bit shorter than the mortise length, Finally I ensure the length is long enough to facilitate easy insertion and removal in the event I’m drilling several holes.

Backer-tenon in place, ready to drill

I use forstner bits when drilling peg holes, because of their superior ability to leave a crisp edge when entering and exiting wood. To ensure this crisp edge, start the drilling slowly until the bit outlined the hole. Than with increasing speed you can drill to the appropriate depth. Raise the bit, without removing it from the hole, while drilling to allow waste to exit the hole; this will prevent clogging during the drilling process. You’ll know if your not doing this often enough, especially if you haven’t clamped your stock to the drill press table, because when you start to remove the bit, instead of the bit exiting the hole, it will lift the stock.

Remove the backer-tenon to reveal perfect mortises.

Remember to "back out" the waste often

Here's a quick video that shows the process:

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