Hard Coat Anodize

[[Me...]]

I'm getting no answers in the Off Topic board so I'll try here...

Have any of you ever dealt with ID grinding/Honing/Machining after Hard Coat Anodize?

Our company is doing it to a few parts due to different anodize specs for separate features and so far it is not working at all. I'm curious as to why our Customer's engineers would require a 16 RA on a finished Hard Coat Anodized surface to begin with but that's just me...

Wouldn't removing the anodize by machining/grinding or honing defeat the entire purpose of the anodize itself?

[[Ma...]]

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I would think so. We've done this to parts before, but never followed by a machining/grinding process. We've mainly used it for protective display purposes.

[[Er...]]

I would guess that the surface need a specific roughness to be able to keep an oil film. If its too smooth it won't lubricate properly. But thats just a guess based on my own experience from racing and working with dirt bike engines. I always honed my nicasil re-plated cylinders and brought them to work for proper inspection, done by my self ofcourse 🙂 I can't remember what surface roughness I aimed at. But it was no where close to 16. How ever, just a tought of possible reason.

If machining defeats the purpouse? Well if you remove it all, yes. It sould depend on how deep it penetrates I guess? 😕 How much do you remove while machineing?

[[Ma...]]

Isn't Ra 16 too much? Or i just bad interpolate?

[[Me...]]

I've seen and dealt with this done on surfaces that require a smooth finish for a moving part interface, like a piston and/or sliding feature, and also that have a tight size tolerance that needs to seal. It's not common, but it definitely has a purpose.

[[Ch...]]

I have measured parts that were coated and then machined smooth.

[[Me...]]

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Machined smooth as in not sure what the RA was?

I'm not particular about the callout of a 16 after anodize myself but I am no engineer...

[[Ch...]]

I honestly don't know the RA. It was on a helical supercharger rotor so finding RA would be difficult. I think my SJ400 could do it but it was unnecessary. We use it for rotating parts that are in close proximity to each other but don't actually touch. The anodizing protects against incidental contact and prevents the aluminum from galling. Machining them smooth allows for tighter tolerances. More for racing/very high performance stuff.

[[Ni...]]

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We do a lot of tooling for the Nuclear industry that requires hard anodizing as well as soft, we've never had to re-machine a surface after coating to improve finish. We always grind/hone etc... prior to coating (grinding will almost always achieve a surface finish of 16Ra or better) and the surface finish is maintained after coating. Could you not machine to print before coating? The coating should have no effect on a surface finish as long as its in spec prior. The hard anodizing coating allowance is another battle that you'll enjoy 🙄

[[Ni...]]

Furthermore the hard anodizing spec will have a coating amount (usually .0008"-.0010"/side) half of that amount will be impregnated into the material and the other half is on top of the surface. So yes machining after will defiantly remove the coating that was just applied and defeat the purpose of said coating.

[[Me...]]

No issues with any other coating besides hard coat.

[[Me...]]

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That's incorrect. Anodize absolutely can change the surface finish. Especially with aluminum.

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Nope. The portion of the anodize that penetrates serves a purpose, even if some of the outer layer is removed.

[[Wo...]]

We are doing that a lot.

First we machine a surface or a hole to a specified dimension.

Then it is hardcoated usually to 0.001" thickness.

The way anodizing works its building up on top of the material to that thickness, and then digs into the material to that thickness.
So in total there is 0.002" thickness.

Then the surface is either lapped or honed to specified dimension/finish. For example 0.0005" of anodizing is taken out.
This way you get a precise dimension and finish, at the same time retaining the hardcoating properties.

For example, we have a hole that we rough machine to 0.501"
Then we hardcoat anodize it - it becomes 0.499"
Then we hone it to 0.5000-0.5004"

Don't know if it helps but that's how I understand it.

[[Ni...]]

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I have to disagree as we have done 1000's of parts with tolerances as tight as 0.0002" all day long and surface finishes down to 16Ra. Never an issue and aluminum is all we have anodized. Now that being said maybe if you leave it close to the limits it will be affected but we achieve finishes better then the print tolerance....which grinding will accomplish if 16Ra is the spec.