Surface roughness after hard anodizing

Thanks in advance... I am an avid reader of this newsgroup (and occasional contributor), and know how much knowledge exists in this
group.
I have some parts that are being extruded and will be hardcoat anodized. They are posts that attach to an aluminum base to batch parts in between processes... a robot will load/unload them from this pallet. The surface finish on the posts should be smooth so as not to scratch the parts if they graze them going in/out of the pallet. I am making 100 of these pallets, which works out to 3000 of these posts...
I am worried about surface roughness... I have seen some parts after anodizing that are pretty smooth and some that were somewhat rough. Is there any special preparation to ensure an Ra 32-40 microinch (give or take) finish?
It seems that the anodizing process would inherently produce a somewhat rougher finish than the bare metal as it creates a layer of oxide... is there any suggstions for what finish I should spec on the bare extrusion?
Any other suggestions along these lines... I am new to the extrusion game. Any other coating suggestions? I need something that is hard, durable and rather inexpensive. I have looked into Nyflor, a Teflon-impregnated coating that is laid down after nickel, but the cost of the coating was 5x more expensive than the total part cost w/ hard-anodize!
Thanks a million...
Adam S
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Adam, The rule is that you get exactly what you give. In other words, every mark shows up after being hard anodized. Every scratch which you cannot feel before will be felt after. Even the best tool finish will look terrible after. My experience is that every piece should be tumbled and then buffed first. Steve

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I worked in a decorative anodizing plant, the other half of the plant did the extrusions. Part of the start of the process was removing the oxide film in a very aggressive hot alkaline bath. Any polish the parts had was gone at that point. Anodizing produces a somewhat brittle surface, any impact will crack the coating. Wouldn't be my choice if I wanted a really smooth surface to avoid damaging parts rubbing on it. From the process books, hard anodizing looks like it gives a pretty rough finish, one process called for sandblasting the parts prior to cleaning, etching and anodizing. And it's only relatively hard, the oxide surface will be hard, the surface under it will be as soft as the original aluminum. If it's not a heat-treated alloy, that can be pretty soft.
We also did powder coating, which would be my finish of choice. These days, you've got your choice of epoxy, polyester or urethane, we never had urethane. Epoxy was the most durable of the finishes we did. Any of them, properly done, will adhere to the surface even when the part is bent double, with no cracking or peeling. If you've got mounting holes in the parts where the hangers could go, it'd be fairly cheap to do on a production basis. Certainly should be cheaper than anodizing. Some experimentaiton would be needed to find out whether epoxy or urethane would stand up better to your proposed use. Properly cured, you can take steel wool to either polyester or epoxy powder coats and only dull the finish, they're pretty abrasion resistant.
How much load are we talking about here? 1 oz. parts or 1000 lb. parts? Might be neither process would be suited to your needs.
Stan
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Thanks for the replies so far. I think I may look into the cost/feasibilty of powdercoating... at least have another alternative to show the powers-that-be...
The parts are only ~.6 ounces, optical-grade acrylic. They are disc-like parts that will be stacked and held captive by these posts.
Anyone ever hear of post-processing hard anod... polishing the softer outside layer down to the harder inner core of the coating? I found a little bit about this online, but it was pretty vague.
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You can make a very durable and hard finish on aluminum. My Porsche has aluminum cylinders (the entire block and head) no sleeves. They do it with a special honing compound Nickasil IIRC. It makes a Nickle Silicone glaze on the aluminum and works quite well for cilinders. I have no clue as to the feasability of putting it on Aluminum Extrusions.
Glenn
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ittle bit about this online, but it was pretty vague.

Glenn, Nikasil is a chemically bonded and etched coating similar to hard anodizing. It must be 'worked' after coating, as the surface is rather rough, very similar to a hard anodized surface.
--
Anthony

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