Type 3 Anodizing

[Zamble]

It was brought up to me that type 3 anodizing a receiver will cause hell with installing the lower parts kit. Is it true, and if so, what could I do to prevent it?

[CHAD PEZZLE]

Type 3 anodizing adds thickness to the material, assuming we're talking about an Ar-15 lower, if you machined the fire control pocket to the exact size of your trigger group then anodizing your receiver would make the pockets too tight.

I've read several differing articles about how much thickness Type 3 adds. It also depends on how long the receiver is left in the solution. I've read it can add any where from .0005" to .003" additional thickness. But your results may vary depending on who anodizes the part. Adding .003" to each side of the pocket just shrunk it down .006" total which might make things too tight.

Theoretically you could account for the difference and machine slightly over sized of what your finished dimension should be. But in all likelihood, unless the lower was machined with a solid vice and rigid machine it's likely that your part is not exactly to spec anyways.

Chad

[Zamble]

Without trying to sound obtuse, what do other people do? Type 2 or 3? Type 2 does not seal the AL, correct? I want my lowers to look and be durable, and not look like crap and surface to look scratched and etc...

[couch]

Take into account the plating thickness, typically Type III Class 2 thickness is .002" including both penetration and build up on surface, so cut everything .002" oversize and the anodize will bring it back down if done correctly to MIL-A-8625.

[Intimid8tor]

I tried to figure this out as well. I wasn't sure if the blueprints take into account anodizing, etc. I found that when machining the lowers, I tended to come out a little over spec without trying. I'll do type 3 anodizing and if there is an issue I will polish the pins. I think you will be fine with normal run out, etc.

[Rusty Scabbard]

Type 2 & type 3 will both seal the Al well. Type 3 gives a harder surface, but type 2 is also pretty hard in it's own right. Type 2 can be dyed any color you want but type 3 is limited to dull and dark. Type 2 made the pins a little tighter on my 10 22 builds but they still could be punched into place without difficulty. I haven't tried anything with type 3. Most info I've found on the web says to oversize holes somewhere between none and 0.001". Some info on anodizing can be found at focuser.com/anodize.html

[kcstott]

The prints I have take into account anodize build up through tolerances. My print shows +-.0015 for the FCG holes and .376" for the selector and .251 for the take down pins. That would be enough for a type III anodize so long as the Anodizer doesn't get carried away.

Anodizing is amperage over time so the longer you leave it in the anodize bath the thicker the buildup. My receivers had .001" over all build up with no issues on pin fit.

[Seesm]

You DO NOT at ALL need to anodize the pocket, selector, hammer, and trigger holes. Just sayin....

[kcstott]

That is true. A civilian owned AR will in most likelyhood never see the round count needed to wear out the holes or corrod to the point of malfunction or failure

[Zamble]

So, Type 3 anodize before milling?

[rero360]

So, Type 3 anodize before milling?

The anodizing will dull your drill bits and endmills extremely fast, I've seen drill bits burn up trying to cut thru type III anodizing. Dull cutting tools lead to crappy finishes and oversized holes and pockets.

[Zamble]

Thank you.

[maker]

You could ream the holes after anodizing if the pins don't fit.