"James Lerch" wrote in message
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One other question, since I don't know the pedigree of the material I
made that threaded adapter out of, what if it wasn't aluminum, but
actually magnesium? (The two materials are difficult to tell apart,
yes?)

No, not really. Magnesium is much lighter and machines totally differently.
It crunches as it cuts, and is quite abrasive, dulling HS tools fairly
quickly. 7075-T6 aluminum displays similar machining qualities, but even
it can be discerned from magnesium once you've machined it.

From your description, I think what you did was hard anodize your part. The
color is a dead give-away. As far as I know, it won't accept a dye finish,
regardless of your attempts. Check it with a file on a corner that isn't
critical and see if it files. Hard anodizing is much harder than a file, so
it won't touch it.

Gorton used to hard anodize the drive pulleys on their mastermils, the
bottom of which was also the spindle brake. They'd run for years in an
industrial setting before needing to be turned and re-anodized. Hard
anodize, unlike other anodizing, can be applied quite thick, and from your
description of the amperage falling off, I think that's exactly what you
accomplished.

I'd love to hear the results of the file test, assuming you're willing to
perform it.

Harold