Need help working hard anodized aluminum.

Forestgnome · Jan 8, 2020

I think I made a big mistake by ordering an aluminum plate that was hard anodized. I was surprised that it wasn't even deburred before anodizing, so now I'm stuck with deburring it myself. I forgot how hard the stuff is, so I tried using a file, which is now smooth. I also need to drill some holes. Any suggestions on what to use to deburr the edges? Any helpful techniques for drilling? Next time I'll have it anodized after machining (head slap).

Milland · Jan 8, 2020

Silicon carbide sandpaper (wet or dry) will deburr edges.

For drilling a cobalt drill will break through the anodize, just press hard enough to deform the skin so it can cut the soft Al underneath.

And keep in mind that hard anodize can decrease fatigue resistance due to the stress risers caused by cracking the hard layer (if that matters in your application).

crossthread · Jan 9, 2020

It probably did not "smooth" your file. It just clogged it up.

DMF_TomB · Jan 9, 2020

anodized layer you can get in different thicknesses. when its very thick its very very very hard.
.
just saying experience with a thin layer you might under estimate difficulties with a thick anodized layer. it aint like 10% more difficult more like 500% more difficult

L Vanice · Jan 9, 2020

Remember aluminum oxide is the same thing used to make many grinding wheels and other abrasives, and will eat HSS tools. It is also, in crystal form, known as sapphire and ruby, just under diamond and silicon carbide on the Mohs hardness scale. Deburring could be done with a belt sander or disc grinder.

For drilling, I would start with a big center punch to crack the hard surface and prevent the drill from skating. A carbide drill could then be used just to get through to the base metal, followed by a normal HSS bit. I have occasionally hand-sharpened a cheap carbide masonry drill on a diamond wheel when I needed to drill in hard material. Costs a lot less than a proper die drill and it is simple to regrind as needed.

Larry

Scottl · Jan 9, 2020

Those little diamond paddles work great for deburring hard anodized aluminum.

Forestgnome · Jan 9, 2020

crossthread said:
It probably did not "smooth" your file. It just clogged it up.

No, it's smooth. I use it all the time to deburr steel, aluminum, and brass. It's a goner.

Forestgnome · Jan 9, 2020

This is hard anodized, so it's pretty thick. I have a plan of attack. I'll try to break through with a cobalt drill, then open it up with a carbide countersink (on order), then drill to size. I had to countersink the holes anyway. Deburr edges with an angle grinder. Thanks for the suggestions.

DavidScott · Jan 9, 2020

Depending on how many holes you need to make I would just use a HSS drill and go for it with a high feed rate if it's not too many. Type III anodize will be hard on any tool, even carbide, so that is why I would use something I could sharpen easily. Even type II will kill carbide tools fairly quickly.

Alox is not just under diamond, BIG difference in hardness there.

Mtndew · Jan 9, 2020

How big is the plate? Can't just buy another plate and cut your losses?
Cutting hard annodize sucks.

Forestgnome · Jan 9, 2020

DavidScott said:
Depending on how many holes you need to make I would just use a HSS drill and go for it with a high feed rate if it's not too many. Type III anodize will be hard on any tool, even carbide, so that is why I would use something I could sharpen easily. Even type II will kill carbide tools fairly quickly.

Alox is not just under diamond, BIG difference in hardness there.

That's the reason I thought I'd try cobalt. Easy to sharpen.

Forestgnome · Jan 9, 2020

Mtndew said:
How big is the plate? Can't just buy another plate and cut your losses?
Cutting hard annodize sucks.

24"x24"x3/8". Aluminum's pretty expensive these days. That was almost $300.

Milland · Jan 9, 2020

Forestgnome said:
24"x24"x3/8". Aluminum's pretty expensive these days. That was almost $300.

Damn, even with anodize that's expensive! The plate is around 22lbs, 6061 should be around 3.50lb, or ~$77. Where are you buying, from McMaster?

EmGo · Jan 9, 2020

L Vanice said:
I have occasionally hand-sharpened a cheap carbide masonry drill on a diamond wheel when I needed to drill in hard material. Costs a lot less than a proper die drill and it is simple to regrind as needed.

We musta gone to the same cheapskate school

This works great and costs a few bucks at the local hardware store, when a good carbide drill will be $30 or more at your tool supplier. When you beat them up blasting through some scummy hard stuff you don't care nearly as much. Plus full carbide shatters pretty easily if you put any side load on it. The masonry ones are more tolerant.

Forestgnome · Jan 10, 2020

Milland said:
Damn, even with anodize that's expensive! The plate is around 22lbs, 6061 should be around 3.50lb, or ~$77. Where are you buying, from McMaster?

Yes, I did buy from McMaster. The problem is when you go oversized, wider than 12", the price skyrockets.

Milland · Jan 10, 2020

I love McM for many things, but not for raw materials. Unless you need a smaller piece next-day, you want to find a local metals supplier that has the stock on site. You'll save a lot of money, especially if you can place larger stocking orders and sit on material for a while (but not too long).

Forestgnome · Jan 11, 2020

It's done! I used a single-cut carbide burr in an air die grinder to deburr/bevel the edges, and the cobalt drill had no problem. Only a little wear after 10 holes. The carbide countersink worked great. Thanks for your help.

Milland · Jan 11, 2020

Good to hear. A little confused that you needed a die grinder to deburr the edges, they must have been pretty rough or you needed more than just an edge break. But whatever works...

Need help working hard anodized aluminum.

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