Drill Walking
Index
Drill walking happens when a bit moves away from the intended hole location as it starts cutting. In metal, that movement can leave an off-center hole, damage the cutting edges, or scrap the part.
Before replacing the bit, check the entry surface, toolholding, and cutting edges. A worn drill may need replacement or reconditioning. An inclined surface may need a flat machined into it or a drill designed for that entry.
Watch when the movement begins. A bit that slides across the surface has a starting problem. If the hole starts in the right place but drifts farther down, investigate what happens as the drill advances.
What to Check Before Replacing the Drill
- Check workholding, runout, and tool length.
- Choose a starting method suited to the operation. Center punching, spotting, and pilot drilling do different jobs.
- For carbide drills, follow the manufacturer's spot-angle recommendations.
- Replace worn or damaged edges, or change the drill design if its geometry does not suit the entry surface.
Why Does a Drill Bit Walk?
An uneven surface or damaged point can make the drill engage unevenly. Runout, loose workholding, and excessive unsupported length can also let it move. Use the symptoms below to decide what to check first.
| Observed symptom | Possible cause | What to inspect |
|---|---|---|
| The bit slips before it starts the hole | Too little starting guidance or uneven contact | Starting mark, surface condition, and drill-point geometry |
| The hole starts off-center despite spotting | Misplaced spot, incompatible point angles, or runout | Spot location, spot and drill angles, and measured runout |
| The drill moves sideways on an inclined or curved surface | One edge contacts first, creating a sideways load | Entry shape and which part of the cutting edge touches first |
| Hole position becomes less consistent as the tool wears | Chisel-edge wear or damaged cutting edges | Drill-point condition and hole quality over the tool's life |
| The drill visibly bends during entry | Unstable holding or excessive unsupported length | Tool length, holder, workholding, and entry loading |
These symptoms can have more than one cause. An off-center hole alone is not enough to conclude that the drill needs replacement.
How to Stop Drill Walking in Metal
Secure the Workpiece and Check Runout
Clamp the workpiece securely. Inspect the holder or chuck, check spindle alignment, and measure runout against the tool manufacturer's requirements.
For hand drilling, apply pressure along the drill axis without pushing the bit sideways.
Use the Shortest Suitable Drill
Choose the shortest drill that can reach the hole and cut to the required depth. Keep unsupported length to a minimum. A starting mark will not compensate for a drill that deflects under load.
Sandvik Coromant's drilling setup guidance recommends short tools, accurate holders, minimal runout, and stable workholding.
Choose the Right Starting Method and Spot Angle
A center punch makes an indentation that helps locate the tip for a conventional drilling start. A spot drill cuts a shallow locating feature. A pilot hole guides a subsequent drill and must match that tool's requirements.
For carbide drills, choose a spot angle that lets the drill point contact before the outer cutting corners. Follow the drill manufacturer's instructions. Harvey Performance recommends a spot angle slightly larger than the drill-point angle and also accepts an equal angle. Guhring gives a specific example: a 142-degree spot for carbide drills with 135- to 140-degree points.
HSS and HSCO drills may need different spotting strategies. Stay within the spotting tool's specified depth. For deep-hole drilling, use the recommended pilot diameter, depth, and point geometry rather than an arbitrary smaller drill.
See Harvey Performance's spot-drilling guidance and Guhring's centering and pilot-drilling recommendations.
Prepare Inclined or Curved Entry Surfaces
On an inclined or curved surface, one cutting edge may touch before the other and push the drill sideways. If ordinary spotting cannot establish a reliable start, machine a flat entry or use a drill designed for that surface.
Sandvik Coromant recommends milling a small flat for substantial inclinations in its solid-carbide drilling guidance. Gühring describes its RT 100 FB flat drill as an option for difficult starts on inclined and curved surfaces. Check the product's application limits and operating instructions before using it.
Consult Sandvik's irregular-surface guidance and Gühring's RT 100 FB application explanation.
Follow the Recommended Entry Conditions
For CNC drilling, set cutting speed and feed for the specific drill, workpiece material, and entry geometry. If the manufacturer specifies an entry-feed adjustment, apply it until the drill reaches the required engagement.
For hand drilling, the DEWALT DWD110/DWD112/DWD115 manual describes starting slowly and applying straight-line pressure without deflecting the bit. Follow the instructions for your own power tool.
Source: DEWALT drill instruction manual.
When Should You Replace the Bit or Change Its Design?
Replace or recondition the drill when wear or edge damage prevents it from meeting your hole-quality requirements. Sandvik Coromant lists chisel-edge wear as a cause of poor centering and recommends regrinding solid carbide tools before wear becomes excessive. Ask the manufacturer or reconditioning service whether the tool can be restored.
A serviceable drill may still be unsuitable for the job. Consider a shorter version if the current tool has unnecessary length. For inclined or curved entries, assess a machined flat or a drill with suitable entry geometry. If the outer corners repeatedly chip after spotting, check the spot angle and setup before trying another drill.
Test any replacement in a controlled machining trial. Start with the candidate manufacturer's cutting data, then compare hole-position accuracy, hole quality, and edge condition with the existing process. Use the same acceptance criteria for both.
Source: Sandvik Coromant's drilling wear and troubleshooting guide.
FAQs About Drill Walking
Why does my drill still walk after center punching?
A punch mark helps locate the tip, but the drill can still move if its point is damaged, its alignment is off, or the workpiece shifts. Check those conditions and confirm that the mark is in the correct location. If the indentation does not guide the selected drill, use a starting method suited to that tool and operation.
Does every hole need spot drilling?
No. Spotting requirements depend on the drill, entry surface, and hole-position tolerance. Follow the drill manufacturer's instructions. A deep-hole drill may need a specified pilot-hole procedure, while the cited DEWALT manual describes using variable speed to start without a center punch.
Will switching to carbide stop drill walking?
Switching to carbide alone will not ensure an accurate start. Carbide drills also need stable holding and an entry method suited to the surface. Sandvik's irregular-surface guidance describes risks of deflection, hole wander, and chipping. Check point geometry, tool length, and entry procedure before choosing a replacement.
Choose a Drill for Your Material and Entry Conditions
When comparing replacements, give suppliers the workpiece material, hole diameter and depth, entry shape, and position tolerance. Include the holder, coolant arrangement, and details of the current problem so they can assess the application.
Confirm the proposed drill's entry procedure and machine requirements with the supplier before putting it into production.