CNC tooling reference
Cross-Hole Burr Control Before Final CNC Bore Finishing
When a radial or angled hole breaks into a precision bore, the burr plan must be decided before the bore is finished—not after inspection finds a scratch or folded lip.
Start from the intersection, not the drill size
A cross-hole burr is not just a housekeeping issue. In hydraulic sleeves, valve bodies, sensor bosses and pump covers, a folded edge can scratch the mating part, trap chips, cut an O-ring or change flow. The drawing may call out only a hole size and bore finish, but the manufacturing plan has to decide which tool creates, controls and verifies the intersection edge.
The safest sequence is usually to leave a measurable bore allowance, drill or interpolate the cross feature, remove the internal burr with a programmed tool, then finish the bore after the risky intersection work is complete.
Feature-to-tool decision map
| Intersection condition | Tooling choice | Why it works | Inspection gate |
|---|---|---|---|
| Small radial oil hole into a hardened bore | Carbide drill undersize, ball-style back-chamfer tool, final fine boring pass | The bore finish tool removes remaining witness marks after the burr is controlled. | Borescope plus bore gauge after final pass |
| Angled coolant hole into nickel-alloy port | Spot drill, coated carbide peck drill, reverse-chamfer cutter with coolant-through holder | Short pecks and reverse chamfer prevent a hot curled burr from folding into the port. | Pin check and magnified port-edge review |
| Polymer metering hole into a soft valve bore | Polished micro drill, air blast, single-lip back-deburr, final light boring or reaming | Sharp uncoated geometry shears instead of smearing a fuzzy lip. | Optical check after rest time |
| Cast iron lubrication cross hole | Carbide drill, dry extraction, small abrasive-free edge break before register finish | Graphite dust is removed before it can recut the sealing bore. | Air blowout, bore gauge and white-cloth wipe |
Practical sequencing rules
Leave bore stock until the burr event is over
If the bore is finished first, drilling the cross hole can push a burr into the finished surface and force handwork. Leaving a small, planned allowance lets the final boring tool restore size, roundness and finish after intersection control.
Do not make hand deburring the only plan
Manual scraping may work on an open edge, but it is weak for hidden bore intersections. A programmed back-chamfer, lollipop cutter, orbital brush or controlled reverse toolpath is easier to inspect and repeat.
Match tool edge to material failure mode
Nickel alloys need heat and work-hardening control. Aluminum needs chip evacuation and built-up edge prevention. Polymers need sharp polished tools. Cast iron needs dust control. The same cross-hole drawing can require very different tooling because the burr forms differently.
Related AXKXA examples
- Haynes 230 igniter boss: angled seal cone and cooling holes
- C360 brass microfluidic valve seat: conical seal and tiny cross holes
- AM 316L hydraulic valve block: deep O-ring ports and internal burr inspection
Use these references as tooling logic examples, not as substitute process sheets. Released drawings, machine limits and inspection rules remain authoritative.