Drill and tap failure troubleshooter.
Tap broke? Threads measured oversize? Chip welding on stainless? Walk through symptom → context → diagnosis. Each terminal node gives causes plus concrete shop-floor fixes for the most common drilling and tapping failure modes.
Built from observation across hundreds of Tier-2 machine shops in India. For specific tap drill sizes by thread, see the drill size chart. For thread engagement math, the thread pitch calculator.
How to use this troubleshooter
Pick the symptom you're observing. The troubleshooter asks 1–2 follow-up questions to narrow the root cause (usually material type, where on the cycle the failure occurred, or the inspection result that flagged it). The terminal node gives 2–4 most-likely causes and a matching list of fixes ranked from cheapest (re-grind, change parameter) to most-involved (change tap geometry, change workholding).
The 8 symptom categories cover the failures that account for over 90% of drilling/tapping problems on a typical CNC shop floor: tap breakage, oversize threads (Go gauge enters but No-Go also enters), undersize threads (Go gauge won't enter), double threading, chip welding/galling, rough finish on threads, drill wandering, and hole oversize. Material-specific fixes are surfaced for stainless steel, aluminium, mild steel, hardened steel, and brass — the five families that account for nearly all everyday Indian shop work.
For deeper reference on tap drill sizes and thread engagement, see the drill size chart and the thread pitch calculator. For bolt-side specifications (torque, grade, lubrication), the bolt torque chart.