When a radial or angled hole breaks into a precision bore, burr control cannot be left until the final inspection bench. The burr may be hidden, work-hardened, smeared into a soft material, or folded directly into the surface that a seal, spool, pin or sensor thread will touch.
The practical rule is simple: control the intersection before the final bore-finishing pass.
A useful sequence
- Rough and semi-finish the main bore, leaving measurable stock.
- Drill, mill or interpolate the cross feature while the bore is not yet final.
- Use a programmed back-chamfer, reverse cutter, lollipop tool, orbital brush or other repeatable edge-control method.
- Inspect the intersection with a borescope, pin or optical method.
- Finish the bore only after the risky burr event is over.
Tool choices by material
| Material condition | Better tooling direction | What to avoid |
|---|---|---|
| Hardened steel bore with small oil hole | Carbide drill, controlled back-chamfer, fine boring after deburr | Finishing the bore first and scraping the burr by feel |
| Nickel-alloy angled port | Coated carbide peck drill, coolant-through holder, reverse chamfer | Long rubbing pecks that harden the exit edge |
| Brass or free-machining copper alloy | Sharp drill, light back edge break, leak-focused inspection | Letting a rolled burr remain near the seat |
| Polymer or filled plastic bore | Polished micro drill and sharp uncoated deburr edge | Dull coated tools that smear or whiten the material |
| Cast iron lubrication hole | Dry extraction, carbide drill, bore finish after dust removal | Coolant slurry that hides abrasive dust |
Why the final bore pass should come late
The final boring or reaming tool should not be used as a rescue operation. It should remove predictable stock after the cross-hole process has already produced a controlled edge. If the cross hole is made after finishing, a hidden burr can scratch the bore, break a seal, or force uncontrolled handwork.
This same logic shows up in several detailed AXKXA examples:
- Haynes 230 igniter boss with cooling holes
- C360 brass valve seat with tiny cross holes
- AM 316L hydraulic valve block with internal burr inspection
The takeaway: assign a tool, a path and an inspection gate to the intersection. A cross-hole edge that cannot be seen, reached or measured should not be treated as an afterthought.
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