Tutorial: Spray Painting Raw Metals

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Joined: 04 Mar 2014, 00:53

Tutorial: Spray Painting Raw Metals

Post by univurshul »

For anyone looking to get paint to stick to those stubborn shiny metal surfaces that reflect unwanted artifacts onto their book scanning platen optics, this is a great solution:

Follow the steps provided and you'll be on your way to a stealth machine.

Any others with good techniques, practice and knowledge about paint products they'd like to share, by all means, we need the input.

IMPORTANT: Safety First! Wear protective clothing, protective eyewear, and a NOISH approved respirator, and always spray outside or in an open garage. I can't stress enough taking the time to protect your health, so follow the instructions provided by the paint accordingly.

I've chosen to illustrate how it's done on a set of the 12" LCD Preview Displays I currently sell in the Agora section of the forum (http://www.diybookscanner.org/forum/vie ... ?f=6&t=543).
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Step 1: Prep any areas you don't want painted. On the LCDs, I use low adhesion blue tape and mask/or use the protective film if it's supplied on the display as pictured.
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Step 2: Lightly sand/buff down smooth and shiny surfaces briefly. If you power sand or polish metals with power tools, make sure the metal is dry and clean. With raw aluminum, I typically wash the pieces with dish soap and water and let them air dry under the sun. Some people use a dry rag to remove loose dust and them wipe the surfaces with mineral spirits. Both work fine as a prep to painting.
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Step 3: Etching Primer. This is a special primer specifically for raw metals. It contains a zinc oxide component and reacts with the metal to etch a layer on the metal's surface; it also is a corrosion preventer. It dries quick. 1 coat over the entire surface of metals --sanded or non-sanded-- is recommended. Follow the instructions on the can.
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If you skip the etching primer step, you might as well forget wasting the money to paint your raw metal components, as the paint will surely peel or rub off over time. Etching the metal is crucial for quality work, it is worth the extra $5-$10 for a can of it. It is hard to find; auto parts stores like Napa carry it. I can't find it at paint stores like Sherwin or hardware stores.

Using etching primer over other paints or an additional coat of etching primer is useless and not cost effective. It is specifically designed to bond to raw metal in 1 coat.
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Step 4: Prime all surfaces. I use dark gray/black automotive primer.
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Step 5: Spray-Enamel All surfaces. This is the final step. It's the darkest your metal can get. 1 coat of flat black enamel should really make the finish clean and professional looking.
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Allow adequate drying/curing time before handling. Remember that paint is a curing/hardening process. Because it's dry to the touch doesn't mean it's ready for wrenches, ratchets, etc. Give it a couple days, maybe 3 if you're in a humid climate.

Crappy paint is generally cheap to purchase. You generally get what you pay for. If the stuff rubs off after you've given it the full treatment, you will likely notice that the lousy layers of paint are rubbed off down to the etch layer. Sand and reapply with a worthwhile product. Rustoleum, Krylon, and Duplicolor are great products, but no one is paying me to endorse, so buy what's a better deal between them.

If you are painting nuts and bolts, leave them bolted in place if at all possible. Or position them as they will appear on the book scanner. (No need to sand down nuts and bolts, see step 3.)
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An ideal painting sequence would be:
[lightly sand & clean between coats for best results)
-self etching primer
-primer surfacer (preferably dark gray or black)
-Flat black enamel coating

About Epoxy Primer: this type generally 'builds' over the surface of what you're painting. It's more expensive than etching primer. That said, it bonds well in certain situations like painting over anodized aluminum.

(I will discuss the methods I use with PlastiDip in a separate post)

No Glare. No Artifacts. No Stress. Excellent Scanning Results.
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Re: Tutorial: Spray Painting Raw Metals

Post by StevePoling »

Great work. The etching primer is a big deal thing to know.

Have you done any experiments with flocking? I've got a vague feeling that that might be less reflective than a flat finish. It would unsuitable for nuts and bolts, but large flat surfaces or those closest to on-axis with the camera bore-site might benefit.
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Joined: 04 Mar 2014, 00:53

Re: Tutorial: Spray Painting Raw Metals

Post by univurshul »

StevePoling wrote: Have you done any experiments with flocking?

No, but that's a fantastic idea, Steve.

I did have this itch to search online for spray-on-felt to coat my Canon A590s

But flocking gel + powder sound like a trial worth conducting. It's fundamental to think that more surfaces/textures of black will absorb more rogue light.

I have plans to 'hood' SAllAS in black cotton fabric with snap rivets.
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