How do I drill a straight hole?

Sighting the drill against two references, the guide tricks that work, and why the first few millimetres decide everything.

Difficulty: beginner
Time: 15 min
Read: 2 min

Short answer

Set the bit, check the drill body against a square from two directions, then hold that. A block of scrap with a pre-drilled square hole makes an instant guide, and a helper sighting from the side is nearly as good.

Drilling straight is a sighting problem. Your eye can only judge one plane at a time, which is why holes wander in the direction you were not watching.

Step by step

Mark the centre precisely.A punch mark in metal, a bradawl point in timber. The bit follows the dimple rather than skating.
Start slowly.The first few millimetres set the direction of the whole hole. Once it is a few millimetres in, the angle is fixed.
Check against two references.Stand a try square beside the bit, sight down it, then move round 90 degrees and check again. One direction alone is why holes look straight from where you were standing.
Use a scrap block as a guide.Drill a square hole through a thick offcut on a pillar drill or with care, then clamp it over the work and drill through it. It is the most reliable low-tech method there is.
Use a drill guide if you do this often.Inexpensive jigs hold the drill perpendicular and set the depth. Worth having for dowelling and repeated work.
Get a helper to sight from the side.They watch one plane while you watch the other. Simple and surprisingly accurate.
Keep your body behind the drill.Arm, shoulder and bit in one line, like sawing. Drilling across your body pushes the bit off square.
Do not lean on it.Excess pressure flexes long bits and pushes the hole off line. Steady moderate pressure and let the bit cut.
Use a pilot for deep or large holes.A small accurate pilot guides the larger bit and dramatically improves straightness.

Tips

Check squareness from two directions, 90 degrees apart. One is never enough.
A drilled offcut clamped over the work is a free and very effective drill guide.
The first three millimetres decide the angle of the whole hole. Start slowly.

Common mistakes

Sighting from one direction only — You correct the plane you can see and the hole drifts in the plane you cannot. Holes that look perfect head-on are often well off from the side.
Pushing hard to speed it up — Long bits flex under pressure and the hole curves. Moderate pressure gives a straighter and faster result.

If it doesn't work

Hole comes out off-line on the far side

Cause: Angle set in the first few millimetres — Fix: Use a guide block, and check squareness from two directions before committing.

Bit wandering at the start

Cause: No centre mark — Fix: Punch or bradawl a dimple first.

Deep hole curving

Cause: Bit flexing under pressure — Fix: Drill a pilot first, ease off the pressure, and clear the swarf regularly.

Questions people ask

Is a drill guide worth buying?

If you do dowelling or repeated accurate holes, yes — they are inexpensive and far more consistent than eye. For occasional work, a drilled offcut clamped over the job does the same job.

How do I drill straight into a ceiling?

Harder, because you cannot sight easily. Use a guide block, or mark the required direction on a scrap held alongside so you have a visual reference.