🚪 DEAD-END BORES · CHIP & COOLANT MANAGEMENT

Blind Hole Deep Drilling

A blind deep hole ends in a flat, dead-end bottom. There is nowhere for chips to go, no through-flow to carry them, and no tool exit to stop the cut. That changes how you choose the method, how you run coolant and how you control depth.

3–200+L/DFeasible blind range

Flat-bottomgeometryDead-end requirement

Depth stoprequiredNo tool exit

Blind headsBTA / ejectorVented systems

PRINCIPLE

Why Blind Changes Everything

In a through hole, chips ride the coolant flow out the far end. A blind hole has no far end — chips accumulate against the bottom, then pack, then break the tool. Every decision follows from that one fact:

Gundrilling handles blind bores well: chips leave through the external V-flute and only the small bottom pocket needs managing. Depth is set by the machine stop.
BTA / STS needs a special blind BTA head with a vented center — coolant returns through the annular gap between the tube and bore wall while chips come back through the tube. The head face is machined for coolant flow at the dead end.
Ejector (DTS) similarly uses a blind adapter so the Venturi still pulls chips back without a through-bore.

⚠️ The bottom pocket: even with vented heads, a small blind pocket of chips stays at the dead end. Plan a finishing operation (spot drill, flat-bottom end mill, or EDM) to clean and square the bottom if the print needs it.

METHOD CHOICE

Choosing a Method for a Blind Bore

Method	Blind-feasible?	Dead-end handling	Typical blind L/D
Gundrill	Yes (standard)	External flute evacuation; depth stop	Up to 100:1+ with whip guides
BTA (vented head)	Yes	Vented blind head + annular return	Up to ~30:1
Ejector (blind adapter)	Yes	Venturi return with blind adapter	Up to ~30:1
EDM	Yes	No mechanical chip problem	Limited by electrode wear

💡 Coolant at the dead end: coolant must reach the bottom to cool the tool tip, then reverse or escape. On blind gundrilling, keep flow moderate so chips do not get compacted; on blind BTA, follow the head maker’s flow spec exactly — too low and chips pack, too high and pressure spikes at the dead end.

DEPTH CONTROL

Hitting the Bottom Safely

Program the stop

Set the machine depth with a generous safety margin on the first article — measure, then adjust.

Reduce feed near bottom

Slow to ~50% feed over the last 3–5×D to avoid breaking through the bottom and damaging the tip.

Monitor pressure

A sharp coolant-pressure rise signals the tool is approaching or packing at the dead end — back off.

Verify

Confirm depth with a gage pin or boroscope; spot-clean the bottom.

✅ First-article rule: never trust programmed depth on a blind bore until the first part has been measured. Whip, bushing wear and machine back-lash all eat into the true depth.

PROS & CONS

Blind Hole Drilling Trade-offs

✅ When blind is fine

Blind bores save material and seal the part end
Gundrilling handles them with standard tooling
Depth can be controlled precisely with a stop

⚠️ When to reconsider

Very deep blind bores need vented heads / adapters
Dead-end chip pockets may need a cleanup operation
Coolant pressure spikes at the bottom
Deep blind + large diameter is hard on every method

APPLICATIONS

Common Blind Hole Parts

🚗 Fuel InjectorsBlind nozzle bores held to microns.

🛡 Valve BlocksCrossed blind passages in manifolds.

🔧 Cylinder BoresBlind hydraulic cylinder bottoms.

✈ ActuatorsBlind actuator housings and pistons.

📝 Oil & GasBlind ports in downhole tools.

🔔 MoldsBlind cooling lines stopped before the parting line.

Blind Hole Deep Drilling

Why Blind Changes Everything

Choosing a Method for a Blind Bore

Hitting the Bottom Safely

Blind Hole Drilling Trade-offs

✅ When blind is fine

⚠️ When to reconsider

Common Blind Hole Parts

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