Enter hole depth and diameter to get the depth-to-diameter (L/D) ratio, the industry classification of the hole, and the drilling method & tooling you should plan on — grounded in VDI 3210 and UNISIG guidance.
Classification and method bands follow VDI 3210 and UNISIG technical references (see the table below). The method recommendation also weighs diameter — below ~Ø20–25 mm, gundrilling is the usual answer; above it, BTA. Treat the output as a planning guide, not a quote.
| L/D ratio | Classification | Typical tooling / equipment |
|---|---|---|
| ≤ 5:1 | Standard hole | Conventional twist drill on a standard machine |
| 5–10:1 | Semi-deep | High-performance twist drill, through-tool coolant |
| 10–20:1 | Deep hole | Deep hole drill with high-pressure through-coolant; CNC machining center possible |
| 20–50:1 | Very deep | Gundrill or BTA; dedicated machine recommended above ~20–25:1 for reliability |
| 50–100:1+ | Ultra-deep | Dedicated gundrilling machine with steady rests & whip guides |
| 100:1 | — | Gundrilling on a dedicated gundrilling machine |
| 200:1 | — | Gundrilling on a high-performance gundrilling machine |
| 300–400:1 | Extreme | Special-geometry gundrills; proprietary processes & equipment |