Symptoms
- Hole ends up in a slightly different spot than marked
- Hole diameter looks bigger than the bit itself
- Bit chatters or bounces when starting the hole
- Edges of the hole look rough or oversized
Likely causes
- CommonNo starter mark or pilot dimple before drillingWithout a starting point, bits tend to walk across the surface before catching.
- CommonSide-to-side pressure applied while drilling instead of straight in-line pressureWobbling the drill enlarges the hole beyond the bit's actual diameter.
- PossibleWorn or damaged bit cutting unevenlyA bit with an asymmetric edge cuts a larger, rougher hole than a sharp, true bit.
- PossibleDrilling at an angle instead of perpendicular to the surfaceEven a slight tilt shifts where the hole ends up and can enlarge its apparent size.
- Less commonBit flexing in very deep holesLong bits can flex slightly under pressure in deep holes, causing minor drift.
What to do
- Mark the center clearly and use a center punch or awl to create a small starting dimple.
- Keep the drill perpectly perpendicular to the surface and avoid any side-to-side wiggling once cutting starts.
- Use light pressure initially to let the bit establish its path, then increase pressure once it's tracking straight.
- Inspect the bit for visible wear or an uneven cutting edge and replace if needed.
- For precise hole placement, consider a drill guide or drill press for critical work.
- On deep holes, back the bit out periodically to clear chips and reduce flex and heat buildup.
Tools and parts
- Center punch or awl
- Drill guide (optional)
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.