Spray Painting Aluminum/Drying Times

As stated previously, this is the first season that we’re considering using spray paint to give our bot some flair. I had done some research work to figure out what types of spray paint would work, where we should paint, how we should paint, how we should prepare, etc. On Saturday I explained our whole bot design plan to the machine tool teacher at the school (founder of PHRED and former mentor). He expressed that in his experience spray painting aluminum (unrelated to robotics) he had flaking issues. Our lead mentor is super cautious, a trait that I think is super valuable, especially on a smaller team like ours. After hearing this (and I expect having doubts already because he does (again, I get this and appreciate it, I realize the value) he became extremely concerned and now thinks we should avoid the spray paint. I get this, AND, I have already read about how other teams have done it successfully. I guess what I’m looking for is a centralized thread of feedback on how we can effectively spraypaint the aluminum box tubing and 80/20 on our bot. It would also be useful to have some estimates on how long parts might have to dry before being taken inside and or worked with. Maybe this could also be a useful thread of info for others trying to spray paint their bot. If you all feel that maybe it’s a better idea to avoid it for our team, I’m open to hearing that.

Thank you, Rufus

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Try the vinyl wrap film used on cars or signs. There is zero drying time. One of the teams in Texas applied it on most of their robot. They said it was pretty easy to repair scratches too. Just cut a piece, stick it on and it is ready to use again. From 5 feet away, the patches were pretty much undetectable.

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For painting, it’s all about proper preparation. Sand, wipe off sanding residue, spray per can directions, let dry per can directions.

There’s a thread or two from within the last year. Can’t recall any search terms… @troy_dietz do you recall that discussion?

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I believe it’s this one: Can you spray paint a bot?

I don’t think it got mentioned there, but trying to spray paint anodized 8020 usually ends badly. Gotta sand through the anodization a bit and prep with a light acetone wipe.

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Best thing to take away from that thread:

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Having done my share of bad spray painting this offseason, I will add this: no matter what you’re painting, the second most important factor (after surface preparation) is patience.

Many light coats are better than one or two thick coats of paint. You can ruin hours of prep time in a few seconds with a heavy finger on the spray button. Don’t try to get full coverage on any pass, know that you will be coming back later to sand and paint another coat.

Which also brings up time. You need to let the coats dry fully, and for best results you need to sand lightly with fine grit paper before the next coat. If you avoid laying the paint down too thick (and if you use the right paint and/or primer) you shouldn’t have to worry too much about chipping.

So this can take a couple days if you do it right. Make sure to budget for that in your build schedule.

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We painted our robot last year and as others have said the prep is key to a good paint job. Sanding and wiping the parts down to make sure it has no oil or foreign materials on it. Also using a good self etching primer is key to painting aluminum, it helps the paint have something to bite into. And yes light coats and a lot of them go a long way with making it look good.

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95 and 3467 discussed some of our techniques in our Build Blog.

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Bring the parts inside to warm up (if you’re in a cold climate) the moment you’re done painting. Curing time will roughly halve for every 10-15°F you elevate the temperature of the parts/paint.

We often start assembly when we reach tack-free time, usually 30-60 minutes. We have the handle the parts carefully, but it generally works out fine.

Often people think our robot is powder coated when they have seen it from the stands or on a webcast, they have to get all the way to our pits to be disappointed!

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I think the tip about “self-etching” primer is a good one. I used it one some parts and they were much more resistant to scratching and flaking.

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This is a topic that my team plans on making a video guide of, but we haven’t gotten around to it yet.

A quick hit on a specific topic that the OP (@Rufus_t_Doofus ) mentioned first - don’t spray paint 80/20. The shape of the t-slot extrusion has too many nooks and crannies, and the anodized layer on the material is both hard to prep and hard to paint. You won’t get a great result. They do sell pre-colored 80/20 in a few different color options (including black).

Otherwise, going to largely echo what others have said so far in this thread.

  1. Prep is key. We hit the aluminum with a wire brush to rough up the surface for better adhesion and remove any anodized layers. We then wipe it down with a rag and some diluted acetone. Isopropyl alcohol or mineral spirits can also work (don’t mix chemicals tho, just pick one). Prep all the surfaces you’re going to paint

  2. Find a good environment to paint in. We’re fortunate to have a maker space/wood shop that has a painting booth with a vent fan. If the parts we’re painting are too large for this, we go outside, but be aware that weather can impact your painting. Store your cans inside and make sure they’re warm before you spray. Since aluminum conducts heat (and thus cold) well, make sure you’re allowing your pieces to dry in a relatively warm area. Obviously don’t attempt to spray when it’s raining or excessively moist outside.

  3. Multiple thin coats is the way to go. Build up coverage over time rather than going heavy-handed. If you spray too heavy, you’ll get an uneven finish and drips in the paint. I suggest using a spray trigger to provide additional control. Use quick bursts of the trigger, and not even necessarily fully depressing it. Always keep moving while spraying, don’t stay spraying the same location.

  4. Add a clear coat after finishing with your colors. Choose a finish you like. Gloss will provide more robust protection, but you can put a matte clear coat over the gloss afterwards if you like. Like step 4, multiple thin coats still works best here.

  5. Once the material is no longer “tacky” it can be handled, although the longer you allow the paint to cure the better your finish will be. Ideally, we paint during one meeting and do assembly during the next. Sometimes schedule does not permit this, so items can be assembled an hour or so after being painted (so long as they are no longer tacky).

  6. It’s designed to look good from the stands, not necessary to look flawless from 12 inches away. Don’t fuss too much about smaller imperfections that you can see up close. It’ll look plenty good when on the field.

One more side note: we generally don’t spray items that are designed to slide or roll against one another. I don’t want paint layers causing increased friction or peeling over time and gumming up linear slides or roller bearings. We didn’t paint our elevator in 2018. We used pre-colored 80/20 on our climbers in 2020 and 2022.

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The right primer is key to painting aluminum so that the paint doesn’t flake off.

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