Sorry if already asked. I searched and didn't see anything. I have a 80% lower that's already been engraved and I want to keep the engravings. Will having it anodized before milling it cover them up?

This is the lower


I am looking to build a T91 clone. My plan is to have it anodized, then mill it, and use Birchwood Casey Aluminum Black to cover the milled areas. Are there any fatal flaws in this plan? Anything I should know?

This will be my first 80%. I have a couple that are already anodized I plan do do first so I (hopefully) don't gunk up the T91 lower.

You will be fine with anodizing the lower.  Done correctly it will "add" to the lower but it is all uniform so it will not cover up the engraving.
Just fyi, Instead of using alumia black on the fire control pocket you can cut lower and have it all anodized at same time or cerakote it.

Apparently I would have to do those things myself, as it's part of the "manufacturing" process. Otherwise a FFL has to do it and put it on the books. Home anodizing is cost prohibitive and Creokote kits are expensive as well, around $200 from what I've seen. Having it anodized before milling is going to cost me $20.

Anodizing adds such a miniscule amount, it's not worth worrying about.
You can have an FFL anodize your lower, after milling. It's not going to make them the Maker/Mfr.
Type 2 anodizing, at home, is super cheap. I do it all the time. If you want Type 3, yeah, go to a professional.

But at that point they have to put it on the books, right? It's no longer a "ghost gun". Not that it matters, I'm legal.

As I understand it, to return an anodized lower if it is completed the anodizer will have to transfer it back on a 4473.

Anodizing could reduce depth if the width is too narrow on the engraving. Seems like it would decrease the depth to a point the width was wider than what the anodizing added to the two sides. It is not just a top and bottom thing.

If you aren’t going to anodize the pin holes and fire control pocket then you are missing some of the benefits of anodizing. If you mill/drill it out and send out for anodizing an FFL will need to log it in with a 4473 and may want your “maker” info engraved, confounding the clone look.

It wouldn’t cost much more to complete machining, treat raw aluminum with chem film (Alodyne), and paint exterior or both inside and out with black moly resin.  It won’t look exactly like anodizing, but goes on thin, covers and adheres well, and is durable. An air brush and oven are main requirements.

What are the rules for a FFL of type # [insert # here]?
If I wanted my firearm anodized, I have to take it to a FFL to do that?

Completed by whom? If the 3rd party is the maker or manufacturer, then they would need to mark it accordingly and 4473-nics it back out. If the item comes in as a Title-I/II firearm, I don't think a 4473 is needed to get it back to the person who brought it in.

Alodine 1200s is no more, it's now Bonderite by Henkel. But no real need for this anti-corrosion treatment. This coating is meant to be primed before topcoat.

Two good home options for 80's. 1) lookup on u toob garage anodizing. Not terribly hard but you need to be cautious and have the right gear and chemicals. 2) use a decent etching primer for AL, then topcoat it with whatever. There's some cautions with #2, like making holes smaller, but you can mask them or lightly sand them back to size (which btw makes for a good custom fit of parts).

You have a few options.

No. To answer the question it will not ruin the laser engraving.  It will however damage laser markings. 2 different things.

Option one: Complete lower and send it out for type III
Requires transfer ect.

Option two: Buy the stuff and do a type II yourself.
It's not hard and the results are good if the aluminum is quality.
Ano is not a coating. It's an oxide that is formed from converting the metal surface. It actually take away from the dimensions.
Good dye and the right temps will produce great results. If you dont like it or screw something up then option 3 can be applied and you have a great protection and base for a coating.

Option three: Paint it. Your choice. cerakote, VHT ceramic, alumahyde.
Just be aware that these are coatings and will change dimensions. The ever popular alumahyde is just appliance paint. Same manufacturer same can.
I like VHT ceramic because it's a bake on coating and has served me well on a few 870s. Cerakote is very thin. I have never used because I ordered all of the "black" color samples they had to look at them and test durability. I was not impressed. The beat was the Elite series E100 blackout. I may do a 1911 in that. Nothing matches perfectly with type III even considering the surface texture as the reflection properties are different so keep that in mind as you may need to do the upper to match. My VLTOR uppers always seem darker than most type III. With any coating it's only as good as the prep.

Option 4. Buy a bottle of aluminum black and go to town. I use it on my lowers that are already anodized after machining. It takes some getting use to and requires some work to get it to stay but you can "rub in" and reapply to get a good finish.

Good luck and have fun.


Edit:
Anodizing works by coverting the metal to a honeycomb shaped oxide that can absorb the dye.
The tempature, amount of current and acid concentration used will determine the change in dimension. Sometimes it can dissolve the metal faster than the oxide is formed and can lead to blotchy color and enlarged dimensions. Typically the loss from the surface is ~50% of the thickness of the oxide when done right.

Micron (µm, one-thousandth of a millimetre.) 0.000039 in freedom units.
25.4 µm = a thousandth of an inch.
Divide the total by 2 for the 50% loss and you know what was gained.
Professional Type IIi at 100µm will see an increase of about .002"
0.001968505" over original dimensions with a 0.00393701" oxide layer.

3 - 5 µm – Protective anodising layer applied before machining or short etching time.

5 µm – Indoor environments with low requirements.

10 µm – Normal indoor stress.

15 µm – Severe abrasion both indoors and outdoors in dry, clean atmospheres.

20 µm – Normal to high stress applications for outdoors such as the transport and building industry.

25 µm – Recommended for high stress such as corrosive environments or abrasion.

40 - 100 µm – Hard Anodising.

I have my in-the-raw 80% lowers engraved with whatever, serialized, etc, then while still in the 80% state, send them out for anodizing.  No detrimental effect on the engraving or its' legibility, depth of the engraving.

then I do the router milling, and then paint the inside.

works for me.

+1

I know Alodine was mentioned. That by itself can be used to keep any raw AL from oxidizing w/o the need for any paint stuff.
My only caution w/ Bonderite (fka 'alodine') is that you 1st need to use the prep solvent or use a light acid solution to clean the surface and then rinse clean before using Bonderite, otherwise the Bonderite does not work 100%.

For a 80%, I don't think bare pocket means anything. Anodized, mill, mask off and then hit the pocket with 1-2 light/dusting coats of a decent etching primer for AL. The white primer in spray can from (Lowes or the like) does very well sticking to AL, I think it's the Rustoleum Industrial Primer for bare AL, locks up very well on bare AL. My only advice for spray, let the sh1t dry for a few days before working with the item. Spray is the simplest way and one can do 50+ 80's. Bonderite is a dangerous chemical, the small bottle can likely do 200 80's, but is pricey and actually has a shelf life.