Drill Bits Selection Operation and Maintenance Guide
Drill bits are the most fundamental cutting tools in machining. Proper selection, operation, and maintenance ensure accurate holes and long tool life.
I. Selection Criteria
- Material: High-speed steel for general drilling. Cobalt steel for harder materials and higher temperatures. Carbide for production and abrasive materials.
- Point Angle: Standard one hundred eighteen degrees for general use. One hundred thirty-five degrees for harder materials. Flatter angles for softer materials.
- Coating: Titanium nitride for general purpose. Titanium aluminum nitride for high-temperature applications. Black oxide for improved chip flow.
- Flute Type: Standard helix for most materials. Fast helix for deep holes and soft materials. Slow helix for hard materials and brass.
II. Operating Guidelines
- Use a center punch or spot drill to start the hole accurately
- Apply appropriate cutting fluid for the material. Cast iron can be drilled dry.
- Use peck drilling cycles for deep holes to clear chips and prevent packing
- Reduce feed pressure as the drill breaks through the workpiece to prevent grabbing
III. Sharpening and Maintenance
- Sharpen drill bits when cutting performance degrades. A properly sharpened drill cuts with moderate pressure.
- Maintain equal cutting edge lengths and angles when sharpening. Unequal edges produce oversized holes.
- Inspect the chisel edge and web thickness; thin the web as needed for reduced thrust force
- Store drill bits in indexed holders to protect cutting edges and enable quick selection
