plating, anodizing, & finishing Q&As since 1989
Removing Anodizing from Threaded Holes
August 27, 2012
Q. I received in some parts that get a blue anodization on them, the 4 threaded holes should be free and clear of anodization according to the prints. We received 17 pieces out of 50 with anodization in the 0-80 UNF 2B holes that I need to try and remove. Any suggestions? Drilling out and using an insert / Heli-Coil is not an option.Scott Scarpiello
QA Director - Bristol, Pennsylvania, USA
A. Threads should never be anodized. The oxide coating goes half in, half out, and on a sharp or thin surface is goes all the way through and flakes off.
Robert H Probert
Robert H Probert Technical Services
Garner, North Carolina
August 30, 2012
A. Hi Scott. In case the implications of Robert's response shot past too fast ...
Anodized coatings on aluminum are not additive, they are both subtractive and additive, roughly 50-50. If you were to strip the anodized coating with no damage to the underlying aluminum at all (using chromic phosphoric acid), the hole diameter will now be bigger by the thickness of the anodizing. On these fairly small holes, depending on the anodizing thickness, there may be no useable thread left, but even if you could rethread it, the major diameter may be too big and out of spec.
Any chance of drilling out -- not for heli-coils but for larger hardware?
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
A. You could perhaps Retap the threaded holes by using the Bottoming taps of the same size as your thread ?Ravi Rao