Troubleshoot common hole machining issues including oversize holes, poor roundness, position error, bad cylindricity. Find root causes & solutions for CNC drilling.

Case Details

Common Problems and Solutions for Drilling / Hole Machining

During CNC drilling with solid carbide drills, manufacturers frequently encounter various hole quality defects.

Below we summarize typical machining problems, root causes, and actionable solutions for daily production.

1. Oversize Holes / Irregular Hole Size

Phenomenon

Hole diameter exceeds tolerance; inconsistent dimension between machined holes.

✅ Causes

Poor clamping of drill, excessive spindle run-out
Asymmetric point angle, offset chisel edge
Excessive abrasion on drill margin
Improper feed rate, insufficient coolant supply

✅ Solutions

Adopt high-precision tool holders & chucks; calibrate spindle regularly
Re-grind drill correctly, check run-out after regrinding
Reduce feed rate appropriately
Optimize coolant supply method and increase flow volume

2. Poor Roundness

Phenomenon

The hole inner contour is out-of-round.

✅ Causes

Non-symmetric point angle, offset chisel edge
Large drill run-out
Excessive clearance angle
Insufficient drill rigidity
Unstable workpiece clamping

✅ Solutions

Re-grind the drill and inspect precision after grinding
Use high-accuracy clamping system & calibrate spindle
Adjust relief angle; select drill with higher rigidity
Firmly fix the workpiece

3. Poor Cylindricity

Phenomenon

Hole diameter changes along the depth of hole.

✅ Causes

Non-symmetric point angle, large run-out
Offset chisel edge
Heavy margin abrasion
Feed rate set too low

✅ Solutions

Re-grind drill and check precision
Increase feed speed to avoid long-time friction of cutting edge

4. Poor Workpiece Surface Quality

Phenomenon

Rough inner hole surface, burrs, built-up edge.

✅ Causes

Insufficient or unsuitable coolant
Excessive feed rate
Heavy abrasion & built-up edge on drill margin
Chip jamming inside flute

✅ Solutions

Improve coolant supply; switch to suitable cutting fluid
Reduce feed rate
Re-grind drills or choose coated carbide drills
Optimize drill flute geometry and adopt step feed strategy to avoid chip jam

5. Low Position Accuracy

Phenomenon

Deviation of hole position; inconsistent hole spacing.

✅ Causes

Low spindle repeat positioning accuracy
Poor drill clamping & large spindle run-out
Machining surface not perpendicular to feed direction

✅ Solutions

Improve machine spindle positioning performance
Select high-precision holders; calibrate spindle before drilling
Adjust workpiece to ensure vertical feed direction

6. Bad Linearity & Poor Perpendicularity

Phenomenon

Hole tilting, hole axis not straight.

✅ Causes

Asymmetric point angle, offset chisel edge, large run-out
Insufficient drill rigidity
Uneven workpiece surface; misaligned center point (lathe processing)

✅ Solutions

Correctly regrind drills and check precision
Use higher rigidity drill tools
Pre-machine flat surface or pre-drill center hole before drilling

Most drilling defects originate from drill grinding quality, tool clamping accuracy, cutting parameters and cooling conditions.
We supply high-performance solid carbide drills, PCB micro drills and deep hole drilling inserts.
If you face persistent hole quality troubles in mass production, send your workpiece material & machining parameters, we provide professional tool selection support.

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