CNC Drilling

CNC drilling produces accurate, repeatable holes using programmed drill cycles, ideal for multi-hole patterns, tight locations, and moderate depth-to-diameter ratios.

Overview

CNC drilling is a computer-controlled holemaking process that uses rotating drill tools to create precise, repeatable holes in metal and plastic parts. The machine follows programmed coordinates to position the tool, control feed and speed, and run canned drill cycles for pecking, countersinking, spot drilling, and more. This delivers consistent diameters, positions, and depths across small to medium production runs.

Use CNC drilling when your part needs multiple holes, tight positional tolerances, or consistent quality across batches. It excels on bolt circles, dowel holes, and hole patterns that would be slow or error-prone manually. You can integrate drilling into the same CNC setup as milling to reduce fixturing and handling. Tradeoffs include higher setup and programming cost than manual drilling for true one-offs, and practical limits on depth-to-diameter ratio before chip evacuation, tool deflection, and cycle time become problematic. Very small or very deep holes may need specialized tools or different processes.

Common Materials

  • Aluminum 6061
  • Aluminum 7075
  • Mild steel 1018
  • Alloy steel 4140
  • Stainless steel 304
  • Titanium Grade 5

Tolerances

±0.001" to ±0.003" on hole diameter, depending on depth, size, and material

Applications

  • Bolt and screw clearance holes in brackets and plates
  • Dowel pin holes in fixtures and jigs
  • Hole patterns in manifolds and valve blocks
  • Pilot holes for tapped threads
  • Locating and alignment bores in housings
  • Cross-holes and ports in machined blocks

When to Choose CNC Drilling

Choose CNC drilling when you need accurate, repeatable hole sizes and locations, especially for multi-hole patterns or production runs. It fits well when drilling can be combined in the same setup as other CNC machining operations to minimize handling. It works best for low to high volumes where programming cost is offset by consistent quality and reduced operator time.

vs Deep Hole Drilling

Choose CNC drilling when your required hole depth is roughly up to 8–10× diameter and you don’t need specialized guidance or high-pressure coolant systems. For standard through-holes, shallow blind holes, and typical manifold patterns, CNC drilling is faster to program, cheaper per part, and can be combined with milling operations in one setup.

vs Manual Drilling

Choose CNC drilling when positional accuracy, repeatability, or part volume matter. If you have tight true-position callouts, multiple datums, or hundreds of identical parts, CNC drilling reduces human error and cycle time. Manual drilling is only competitive for very simple, low-quantity work with loose tolerances.

vs CNC Milling (circular interpolation)

Choose CNC drilling for true cylindrical holes at standard sizes, especially when depth is significant relative to diameter. Drilling is faster and easier on the machine than helical milling for most basic holes. Reserve circular interpolation for oversized bores, non-standard diameters, or when you need very fine control of hole geometry and surface finish.

vs Laser Cutting

Choose CNC drilling when you need accurate, straight holes with controlled diameters and depths in thicker sections. Drilling gives better wall quality and diameter control in metal blocks and machined parts. Laser cutting suits thin sheet profiles and small holes in flat stock, but struggles with deep, straight bores in solid material.

Design Considerations

  • Use standard drill sizes where possible to avoid custom tooling and reduce cost and lead time
  • Keep depth-to-diameter ratios under about 8–10× for conventional drills, or flag deeper holes clearly so the shop can plan tooling and cycles
  • Specify realistic tolerances; tightening diameter or true-position beyond what the function needs will drive up cost and inspection time
  • Clearly call out hole type (through, blind, counterbore, countersink, threaded) and depth reference (from surface or from bottom) to avoid ambiguity
  • Group holes by size and depth in your drawing to simplify programming and reduce tool changes
  • Provide adequate tool access and avoid placing holes too close to edges or other features, which can cause breakout, burrs, or weak sections