Grinding hard anodize type III to size?
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  1. #1
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    Default Grinding hard anodize type III to size?

    Hello friends!

    I have a new challenge ahead;

    we need to make a few parts that have a drawing callout of grinding after hard anodize (around 0.002-0.003" thick) with a surface finish of N4.

    1. parts are tube shaped, around 3" long, 2" diameter. the grinding callout is both ID and OD.
    2. one part has a critical datum to which a few true position holes are located to and it represents a 90 degree step to the OD - and the final dimensions will be reached after anodize of course...
    3. tolerances of ID and OD are in a tolerance window of 0.0003".

    I plan to make the parts on a multitasking machine, complete them with consideration of the anodize so that I will have about 0.0004" to take off the diameters.

    Now the question is:
    Should I use grinding to do that as the drawing calls for?
    Can I turn the coating to size with a PCD/diamond turnin insert and maintain the desired N4 finish using lopping/polishing compund?

    Any other thoughs? experiences with hard anodize grinding or sizing?

    Thank you for you time and help!

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    I'd be interested in hearing differing experiences, but I think you will get nowhere trying to turn the anodize layer. The anodize layer is basically a very hard mineral with a much tougher substrate than any normal rock. It's not going to deform and make chips the way metal does. Rather, it will shatter, chip and crack.

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    Try honing I.D. first, then grind O.D., on freshly ground arbor if you can.
    I have ground O.D.'s with al-oxide wheels. Since you are only removing a tenth or two per side you should have no trouble.

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    I've done something similar using a cast iron lap and diamond rolled into the lap. This is very different than lapping with a slurry. It's old school but it works. Also see American Lap Company

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    You should pre-grind or pre-hone the ID and pre-grind the OD. Pre grind so your finish is equal to or better than your finish product. Make and excellent part to start with so you will get a good part after the anodize. Anodize does not always go on evenly I don't care what the platers say. I have had good luck grinding hard anodize with a Pink wheel 60-80 grit J hardness that is very open structure around 15.

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    Thank you for your input.

    I was planning to finish the part with considaration to coating thickness with a 0.0004" feed per revolution,
    perhaps with a diamond turning tool to meet the best surface I can which will be the base onto which the coating will build up.
    it is still required to have an N4 surface finish after anodize so some sort of lapping/grinding must be done after coating.

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    I think grinding will work better than any other form of machining here. And keep in mind you are machining aluminum oxide, so use something harder to machine it, preferably diamond. How fast can you spin your tools on your multitasking machine? You could run mounted diamond grinding tools to finish on the machine you made the part on.


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