A bright aluminum surface is not proof of a functional sealing land.
Long-wave flatness error, smeared aluminum, a small toolpath-join step, or chips dragged across the last pass can remain visible only in measurement or contact testing. PCD helps by holding a sharp, abrasion-resistant edge, but its value depends on matching the edge to the feature.
Choose the PCD format by function
- A broad sealing land favors a balanced face mill with controlled wiper geometry.
- A high-silicon aluminum bore may justify a positive-rake PCD boring or reaming edge.
- Interrupted casting skin should often be removed with a sacrificial carbide tool before PCD finishing.
- A path that crosses a steel insert should stop before the ferrous boundary and continue with another tool.
PCD is not automatically the correct answer for every aluminum job. A sharp uncoated carbide cutter can be more practical for low-volume interrupted work, very small features, or a setup that cannot protect the diamond edge from impact.
Protect the datum during the last pass
Measure runout at the cutting edge rather than the shank. Keep the finish path continuous, evacuate chips away from the completed surface, and do not rely on hand blending to repair a functional seal. If the rough stock contains skin or interruptions, separate cleanup from finishing.
Inspect function rather than shine
Record flatness, waviness, Ra, bore geometry and contact pattern as required by the drawing. Trend edge notching, microchips, aluminum adhesion and surface drift to set a replacement gate before the tool damages the work.
The full selection table is in this five-language PCD aluminum tooling guide. For adjacent decisions, compare high-speed aluminum chip evacuation and wiper geometry for production finishing.
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