A cooling hole that exits beside a feather-seal slot creates a sequencing decision. Open the slot first and the drill may break into an unsupported edge. Drill first and the temporary slot stock can support the final ligament—provided the slot later removes the controlled breakout zone.
That means the final intersection, not a generic operation order, should decide the process.
Overlay the hole and slot before selecting a tool
Record the hole axis, slot wall, effective drilling depth and remaining ligament at breakthrough. In a brittle intermetallic, ceramic or notch-sensitive heat-resistant alloy, that ligament can control whether the exit shears, forms a burr or breaks away.
Diameter alone is not enough to choose the drill.
Keep temporary support where it helps
When the drawing allows it, leave the adjacent slot closed during drilling. Use a short micrograin carbide drill with minimum projection and a reinforced point. Prepare a curved or oblique entry with a small flat mill or compatible spotter; an oversized spotting cone can guide the drill off-axis.
Reduce feed before the last ligament fails. Waiting for a spindle-load spike can be too late because the edge may fracture before the control reacts.
Pecking helps only when each withdrawal actually unloads chips. Re-entry can rub a heat-resistant alloy or drive fragments against the exit.
Remove support with low lateral force
After drilling, open the slot with a tool and path that do not pull the thin wall toward the cutter.
- A fine-tooth carbide slitting cutter suits a straight narrow slot.
- A small trochoidal end mill can follow a curved slot when radial engagement and runout are controlled.
- A separate finishing allowance lets the wall be corrected without forcing one tool to rough, release and finish the fragile edge.
Inspect after both features are complete
The useful inspection is not the hole before slotting or the slot alone. Measure edge loss, hole diameter and slot-wall position after the intersection is exposed. Use optical inspection, a borescope or CT only where the access and risk justify it.
Growing exit chips, directional burrs, rising thrust or diameter drift should trigger tool replacement before the edge breaks unpredictably.
These drawing-based cases show how the same support principle changes by material:
- Gamma TiAl shroud with feather-seal slots and cooling holes
- Silicon nitride bearing cage with thin windows and edge-chip control
- 96% alumina nozzle plate with micro-orifices and inlet pockets
Preserve support until the hole crosses its most fragile boundary, then remove that support with the lowest-force slotting operation that meets the drawing.
Top comments (0)