Use a DIY Guide Block or Square

Build a simple L-shaped guide from two scrap hardwood blocks joined at a right angle. Press the drill bit into the inside corner and the two perpendicular faces prevent the bit from tilting in either direction, keeping your hole at 90 degrees.

Steps

1. Join two flat, square-edged hardwood blocks at a precise right angle using glue or screws
2. Verify the inside corner with a combination square
3. Clamp the guide to the workpiece with the corner aligned on your mark
4. Press the bit firmly against both inside faces and drill at slow speed
5. Once the bit is 1/4" deep, the hole itself guides the rest

Tips

• Use hardwood (oak, maple) so guide surfaces stay accurate longer
• Pre-drill a perpendicular hole through the block on a drill press to create a reusable bushing guide
• A speed square held alongside the bit serves the same purpose in a pinch