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Old 09-26-09, 05:30 PM   #1
Rainier22
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ANOTHER painting question

I looked at all sorts of painting threads, but I didn't see exactly what I was looking for. I'm painting a Scott AF-4 handlebar. Svr found a good picture of the model.

What is this handlebar for?

I'm sanding her down for a new painting. So far, I've used my Dremel to sand off the paint, but it left a fairly rough surface. I sanded it down with some 60 grit and then some 150. There are definitely some grooves, at the most half a millimeter deep. The vast majority are at the max half that deep. I'm curious exactly how smooth metal needs to be for a good painting.

I'm just doing some spray paint primer, Rustoleum, and clear coat. Speaking of clear coat, I'm curious if there's a difference between lacquer and enamel. The hardware store recommended enamel, but they don't exactly go around painting bikes.

Thanks in advance. If there is a thread that answers this, feel free to point me there and delete this one.

Note: I will not be taping the bar as much as the handlebars depicted. Also, the grooves are at a max probably a millimeter wide in one portion where I used a wire brush for sanding. I also have a brush add on to the Dremel that makes the metal very, very smooth, but it would take hours to go over the entire bar with it.

Last edited by Rainier22; 09-26-09 at 05:36 PM. Reason: Note at bottom
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Old 09-26-09, 05:39 PM   #2
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You want 600-grit for primer. And you'll need two types of primer:

1. zinc-chromate chemically bonds to the aluminium, but doesn't have much thickness, then

2. regular thick sanding primer next. Let try and sand smooth with 600 then 1000-grit wet

3. apply paint, wet sand between coats if you want really glossy finish, requires letting paint dry enough to do so

4. apply clearcoat

Last edited by DannoXYZ; 09-26-09 at 06:38 PM.
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Old 09-26-09, 06:24 PM   #3
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I looked up what 600 grit would look like and got this.
http://www.arscives.com/bladesign/Images/b.600gritw.jpg

To get something like that would easily take another five hours of work. I never thought of my skin as being weak, but I already have a blister from sanding down to 150 grit. Is there some sort of machine you use for this?

Also, when you say 600 grit for primer, do you mean that 600 grit is smooth enough for paint, or that 600 grit is necessary to begin adding primer?
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Old 09-26-09, 10:55 PM   #4
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You can get away with going down to 400-wet as it wears out and becomes more like 800. Problem is rougher grits is you end up with scratch marks in the final paint.

You can get sandpaper on cloth in 1" strips. Really good for wrapping 360-degrees (with 45-degree angle of approach) around tubing and you just floss back and forth.
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Old 09-26-09, 11:51 PM   #5
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Thanks DannoXYZ. I clearly didn't know how much work I was getting myself into. After reexamination, it looks I'll be taping my bars pretty well the same as the bars in the picture Svr showed. So I think I'll sand down the portions I won't have under tape as smooth as you described. The rest I won't worry so much about.

Thanks again.
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Old 09-27-09, 05:38 AM   #6
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Quote:
Originally Posted by Rainier22 View Post
I'm sanding her down for a new painting. So far, I've used my Dremel to sand off the paint, but it left a fairly rough surface. I sanded it down with some 60 grit and then some 150. There are definitely some grooves, at the most half a millimeter deep. The vast majority are at the max half that deep. I'm curious exactly how smooth metal needs to be for a good painting.
Scratches that deep will need to be filled or they'll show under the paint. I'd use auto body filler then resand. On a round handlebar it might not be the easiest thing that you've ever done.

I'd stick with enamel clear coat. Lacquer may cause the new paint that you've just applied to lift.
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Old 09-28-09, 03:14 AM   #7
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Even with an aesthetic coat of paint or bar-tape, I would still sand down the bar to a very fine finish and polish it. Scratches on the surface of aluminium seriously compromises the strength as the scratches are stress-risers that will generate cracks. Each and every single scratch is a potential crack and many of them will propagate... then when they meet...
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