Drilling

Drilling creates round holes with rotating cutting tools, delivering accurate diameters and depths for fastener, clearance, and fluid passages in prismatic and turned parts.

Overview

Drilling is a machining process that produces round holes using rotating cutting tools, typically on CNC mills, drills, or lathes. It is the standard way to create fastener holes, clearance holes, dowel locations, and fluid passages in metals and plastics with consistent diameters and depths.

Use drilling when you need straight, cylindrical holes with standard sizes and moderate to tight tolerances at low to high production volumes. It is fast, cost-effective, and easy to fixture, especially for through holes and shallow blind holes. Tradeoffs include limited ability to create non-round or highly interrupted features, reduced accuracy on very deep or tiny holes, and potential for burrs that may need secondary deburring. Proper selection of tools, speeds, feeds, and coolant keeps costs low and hole quality high.

Common Materials

  • Aluminum 6061
  • Steel 1018
  • Stainless 304
  • Titanium Grade 5
  • Brass C360

Tolerances

±0.002" to ±0.005"

Applications

  • Bolt and screw clearance holes
  • Tapped and pilot holes for threads
  • Dowel pin and locating holes
  • Manifold and coolant passages
  • Jigs and fixtures with pattern holes
  • Mounting and alignment holes in brackets and plates

When to Choose Drilling

Choose drilling when your part primarily needs standard-size round holes with straightforward access and moderate depth. It excels for bolt patterns, manifolds, jigs, brackets, and repetitive hole features across low to high volumes. It is ideal when you can design around standard drill sizes and reasonable tolerances instead of custom reaming or grinding.

vs Milling

Pick drilling when you need simple, straight, round holes and can align the part for direct tool access. Drilling is faster and cheaper than milling circular pockets or interpolated holes for most standard diameters. Use milling only where holes must be non-standard shapes, large diameters, or have features like keyways and counterbores that cannot be done efficiently with drills alone.

vs Turning

Choose drilling on a mill or drill press for holes in prismatic parts, plates, and brackets that are not easily fixtured on a lathe. Even on turned parts, drilling is the preferred method for axial holes; turning only handles external diameters and faces. Use turning for the OD and faces, then drilling for internal axial features to keep cycle time and tooling simple.

vs Grinding

Use drilling for general-purpose holes where standard tolerances and surface finishes are acceptable. It removes material far faster and at lower cost than grinding. Only move to grinding if you need extremely tight diameter tolerances, very fine surface finish, or hardened holes that drilling cannot hold accurately.

vs Electrical Discharge Machining (EDM)

Select drilling when your material is machinable with standard cutting tools and hole geometry is accessible and not extremely deep or tiny. Drilling is much faster and cheaper than EDM for typical fastener and fluid-passage holes. Reserve EDM for very hard materials, difficult access, ultra-small holes, or complex paths that drills cannot follow without deflection or tool breakage.

vs Broaching

Choose drilling when you only need round holes without internal profiles such as splines, keyways, or hex shapes. Drilling requires simpler tooling, less setup, and is economical for a wide range of diameters and depths. Use broaching when you must form internal shapes or drive profiles, typically starting from a drilled pilot hole.

Design Considerations

  • Use standard drill diameters wherever possible to avoid special tooling and reduce cost and lead time
  • Maintain adequate edge distance around holes (typically ≥1–1.5× diameter) to prevent breakout and improve fixturing
  • Keep depth-to-diameter ratios modest; for deep holes specify if gun drilling or peck strategies are acceptable
  • Call out hole depth and type clearly (through, blind, drill-to, drill-and-tap) and reference from a machined surface
  • Apply realistic tolerances on diameter and position; reserve tighter limits only for critical locating or press-fit holes
  • Group hole sizes and depths to minimize tool changes and setups, especially in large patterns or production runs