Dave,
The blue tape method is my favorite as HokieKen and MikeB said, fast and easy, BUT ...........
You already have a great depth stop in your shop, scrap wood.
Make a block of wood, sized to permit drilling a hole through it with the drill bit being used, then slip it on the bit, measure from tip to depth needed - mark the block, remove and cut so when installed only the desired depth dimension of the bit is exposed. Can't drill any deeper than desired, the block will see to that.
Have a great day making holes.
PS: if you want this to stay on when drilling vertically, stick masking tape, or a toothpick in the hole for a tight fit. If you use a dowel in lieu of block, you won't even see it spinning. Good luck.