Enlarging Countersink In Hard Anodized Al?

The anodize is very hard but on a relatively soft aluminum. So a regular countersink will work. If you are still concerned, use a drill to remove the anodize and then the countersink to got the right shape.

Dan

Gunner Asch wrote in news: snipped-for-privacy@4ax.com:

I'm pretty sure this is Type III hard anodizing, which is A) sapphire (about as hard as tungsten carbide), and B) can be as much as 0.005" thick. I doubt this is super thick, but it's not just a decorative corrosion inhibiting layer. It's designed to provide wear protection in a low force sliding application.

I can estimate the problem when I drill out the holes. If it cuts easily & doesn't trash my drill bit, I can try a regular countersink.

Doug White

" snipped-for-privacy@krl.org" fired this volley in news: snipped-for-privacy@googlegroups.com:

Or just an abrasive cone, like a 60-degree cone-shaped rotary stone. All you need do to protect the edges of your countersink is buzz through a half-mil or so of that aluminum oxide to get to fresh metal.

However, Dan is correct that just applying enough pressure (from the start) with the countersink will crush the oxide by embossing it into the soft aluminum. So you'll actually not be cutting much if any of it; just the aluminum underneath it.

Lloyd

Gunner mumbled:

No... it's aluminum oxide (sapphire). Harder than most other substances, and harder than most any metal.

It's BRITTLE and weak, but certainly not softer than hss.

LLoyd

We regularly add 10-32 countersunk through holes to 0.160" thick 6061 sheets that have been Type III clear anodized for, as Doug said, wear protection in a relatively low force sliding application as well as corrosion protection. The hardcoat anodizing is about 0.0015" thick in our case. We do this in a Fadal cnc mill with TiN coated hss drills and hss countersinks and use the same drill program that we use when we do it before the anodizing, and haven't ever noticed any issues. Oh, flood cooling with soluble oil coolant, if that matters.

----- Regards, Carl Ijames

Gunner Asch wrote in news: snipped-for-privacy@4ax.com:

I'm pretty sure this is Type III hard anodizing, which is A) sapphire (about as hard as tungsten carbide), and B) can be as much as 0.005" thick. I doubt this is super thick, but it's not just a decorative corrosion inhibiting layer. It's designed to provide wear protection in a low force sliding application.

I can estimate the problem when I drill out the holes. If it cuts easily & doesn't trash my drill bit, I can try a regular countersink.

Doug White

"Lloyd E. Sponenburgh" wrote in news:XnsA30E55BCB1D73lloydspmindspringcom@216.168.3.70:

OK, I'll give it a shot & use a regular countersink. I'm guessing it isn't super thick. It sounds like a single flute would apply the most pressure to break up the oxide, so I can start with that. I normally use 6 flutes to minimize chatter, and I think that would tend to skate more than cut on this stuff.

Doug White

Thanks!

Yes, that might work. I modified some pre-made anodized plates with a solid carbide end mill, and it ate the end mills VERY quickly. I was quite upset. I had 2 9-pin connector holes to mill out, so, maybe 4-5 INCHES of linear milling, and that pretty much totalled a brand new 1/8" end mill. This was a production job, too.

So, you really need to get rid of the anodizing somehow.

Jon