Drill Troubles: Causes and Remedies
During drilling operations, several problems may occur that affect the accuracy of the hole and the life of the drill. These problems are known as drill troubles. Understanding their causes and remedies helps maintain efficient drilling operations.
Common Drill Troubles
| Problem | Cause | Remedy |
|---|---|---|
| Drill overheating | Excessive speed or insufficient lubrication | Reduce speed and apply proper cutting fluid |
| Drill wandering | Incorrect drill point or improper marking | Use center punch and correct drill grinding |
| Rough hole surface | Dull cutting edges or improper feed | Sharpen drill and maintain proper feed rate |
| Drill breakage | Too much pressure or incorrect alignment | Apply proper feed and maintain alignment |
| Oversized hole | Unequal drill lips or worn drill | Grind drill properly and maintain equal lips |
Important Drill Geometry Factors
Proper drill geometry ensures efficient cutting and accurate holes.
Equality of Lips
The two cutting edges (lips) of the drill must be equal in length and angle. If the lips are not equal, the drill will cut unevenly and produce oversized or inaccurate holes.
Correct Clearance
Clearance angle is provided behind the cutting edge of the drill. It prevents friction between the drill and the workpiece and allows smooth cutting action.
Dead Centre
The dead centre is the point where the two cutting edges meet at the center of the drill. It does not perform cutting but helps guide the drill during drilling operations.
Length of Lips
The lips of the drill should be of equal length. Unequal lips cause uneven cutting and may lead to drill vibration and inaccurate holes.
Kinds of Drills
Drills are classified based on their size and measurement systems.
Fractional Drills
Fractional drills are measured in fractional inches such as 1/8", 3/16", or 1/4". They are commonly used in countries using the imperial measurement system.
Metric Drills
Metric drills are measured in millimeters such as 3 mm, 6 mm, or 10 mm. These drills are widely used in most modern engineering workshops.
Letter Drills
Letter drills are identified by alphabetical letters from A to Z. They provide intermediate sizes between fractional drills.
Number Drills
Number drills are designated by numbers ranging from 1 to 80. They are mainly used for precision drilling operations.
Grinding of Drill
Grinding of drills is performed to restore sharp cutting edges and maintain proper drill geometry. This operation is usually carried out on a bench grinder.
Steps in Grinding a Drill
- Hold the drill firmly with both hands.
- Place the cutting edge against the grinding wheel.
- Maintain the correct point angle (usually 118° for general drilling).
- Grind both lips equally.
- Ensure proper clearance behind the cutting edge.
- Check symmetry of lips after grinding.
Precautions During Grinding
- Maintain equal lip length.
- Avoid overheating the drill.
- Use cooling water if necessary.
- Check the drill angle frequently.
Conclusion
Proper maintenance of drills and understanding of drill geometry are essential for efficient drilling operations. Identifying drill troubles and applying the correct remedies improves drilling accuracy, increases tool life, and ensures better machining results in engineering workshops.