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Effect Of Hardcoat Anodize On Internal Screw Threads

2003

When applying hardcoat Anodize per AMSA8625 F, Type III, (.002 ±.0002 Thick), to relatively small parts with internal miniature screw threads, (0-80, 1-64 and 2-56), is it safe to assume the threads will build-up uniformly? Please note the threads are both blind and thru.

Scott Johnson
- Florida

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No, that's not a safe assumption. Simply getting those blind holes to neither trap solution nor air bubbles will be your first problem. Do they really need to be anodized?

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2003

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The thickness of the anodic crystal in the threads will be a function of the solution circulation thru the holes, better on the thru holes, almost zero in the blind holes.

The anodic crystal builds perpendicular to the surface, therefore on the cutting edge of the thread you will have a spreading gap with two very thin crystal layers on each side. Then when you apply the mating thread the anodizing will flake off and/or jam against the mating thread and gall.

Threads should be plugged. Nobody anodizes threads.

Anodizing should never be applied to a sharp edge or corner, all corners should be radiused.

Robert H Probert
Robert H Probert Technical Services

Garner, North Carolina

2003