Check how deep a hole is relative to its diameter, the single biggest factor in whether a straight drilling pass will work or whether you need pecking or a specialized deep-hole tool.
Ratio = hole depth / drill diameter. Below about 3:1 a straight pass is usually fine, 3:1 to 8:1 typically wants pecking, and beyond 8:1 to 10:1 starts to need gun drills or other deep-hole tooling.
How it works
As a hole gets deeper relative to its diameter, chip evacuation, coolant delivery, and drill deflection all get harder at the same time. The ratio alone does not guarantee success or failure, but it is the first number experienced machinists check before committing to a strategy.
FAQ
Does material change these thresholds? Yes, gummy or work-hardening materials push the safe ratio down, while free-machining materials with good chip breaking can sometimes go a bit deeper before pecking is required.
Related Guides
CNC Calculators · Peck Drilling Calculator · Drill Point Depth Calculator