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HVLP Question

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pauldan181

Well Known Member
I'm using AFS waterbase products and had good luck with the priming
process with my old cheapie suction gun. Now it's time for the color coats
and I bought a Devilbiss gravity HVLP gun. Both the instructions with the gun and Dan at AFS recommended 20 psi at the gun with the trigger pulled. OK fine, except to achieve this it takes a line pressure of 80 psi. At these pressures I'm blowing parts off the table and putting a lot of overspray in the air. Maybe I'm just used to rattle cans and my suction gun which works great
with a line pressure of 40 psi. Is this the way these conversion guns work?
It feels more like sandblasting than painting. My question is this, does 80 psi
with the trigger NOT pulled sound right?

Paul Danclovic
Carver, Minnesota
"Painting" 8A
[email protected]
 
He most likely means 20 psi at where you plug the air hose in. Generaly you only want no more than 10 psi at the air cap. To messure that you need a special air cap that has a pressure gauge on it used just for set up. Try installing a mini regulator on the gun and adjust it to 20 psi on its gauge.
 
Paul,
I think you have it right. I have a pretty high end Devilbiss gravity HVLP gun too. That is how it works. They take a lot of air.

Lets say you were painting the side of the house with this thing (never). You're going to be walking down the side of the house with the trigger fully pulled. Now, the HVLP gun spec is for a max *continuous* pressure of 10lbs at the cap. You're gun probably has stamped on the cap something like "max 30 lbs inlet pressure". That is the exact *continuous* pressure at the hose entry into the gun that produces the magic (legal) 10 lbs at the cap. I'm assuming that you have a gauge and small regulator at the base of the gun handle (inlet). How long after you begin a full trigger pull does the gun gauge drop from the very high static pressure down to something like 30 lbs? Answer: Immediately.

Hence, it is totally true that you set the gun inlet pressure with the trigger pulled. It takes a lot of static hose pressure on the relatively small inlet to produce the gun volume for proper atomization and fan spread.

Cheers,
Scott
 
Something isn't right. Where are you reading the pressure at? My compressor reg is set wide open (probably around 90, the gauge is clouded over), I've got a regulator at the gun inlet which usually reads around 25 psi without the trigger pulled and about 20 with it pulled. If I open things all the way up, you're right--it's a sandblaster. It definitely shouldn't be that way. In fact, it should feel a lot softer than the spray from a conventional gun.
 
Another AFS guy

Hearing about another person who's using the AFS paints like I did, I just had to chime in on this discussion. The inputs from other painter/builder/pilots in this thread seem to be excellent, but I can add some personal AFS specific recommendations. I'm by no means an expert, but my plane did come out nice after some trials, so I think you might get some useful feedback here.

I have an older Devillbliss Finishline gun and my numbers seem to be about 60 psi at the water separator gauge, and 30 psi at the gun gauge with the trigger pulled. This is probably a little higher then some people use. I was told by the Hanger 21 guys that unless you can get a really fine tip (1.0-1.2), then you'll need a bit higher air pressure to get good atomization. The newest Finishline gun comes with a stainless steel nozzle instead of a plastic one, which allows for smaller nozzle sizes.

If the pressure is way up (80 psi at the gun.,..yikes!) you will blow away much of the paint, and you can also get orange peel texture. Also, low air pressure makes for splotchy un-atomized coats.


A little bit off subject but related, I will add a few general tips for spray painting with this brand of paint.

If there is any one thing I would recommend to someone using AFS paint on their bird.... it is to not spray it on too lightly... I did exactly that on my first top coat of Juno White and had to add a complete second coat to the whole plane. It was not a disaster because AFS paint does add coats beutifully on top of its self. Yes, runs can happen on vertical surfaces with wet coats but you have to risk it a little. If your hand speed is right, and you have done your earlier light coats to a nice tacky feel, then runs won't happen.(sounds good in theory...haha). I learned the hard way that proper technique is to get your bright lights positioned at the right angle, and see the gloss as it developes in the wetting faze. A little texture is good as long as it gets very glossy as well. If you don't get the wet look it won't dry glossy.

Also, watch the room temperature of your painting area. I had problems with both cold spray sessions (below 60 f),and warm ones (above 80f).

The other thing which you probably already do is to clean your gun well after every spray session which includes taking off some of the smaller parts.

Also, here's my e-mail address if you want to discuss my RV6A AFS paint story. It has a happy ending eventually. I also have pictures of my four color paint job (juno white, metallic blue, bahama blue, and dawn patrol grey). I could e-mail you a couple if you would like. [email protected]

good luck, Clark
 
Paul,
I just wanted to second what Clark said. I have not completed painting my 7A, but I have experimented quite a bit on the tail pieces. I have also gotten a few pointers from a few other builders, all of which have said almost the same thing. The key to getting a good finish with the AFS topcoat is to lay on the first coat fairly light and wait until you get a good tacky finish. Then the next few coats need to be fairly heavy to get the glossy finish. If that first coat is not tacky, then it will not hold the heavier coat on vertical pieces. If it dries too long, then you need another first coat.

The AFS paint definitely takes a little practice to get the process down, but I think you will be very satisfied with the final result if you are patient. Don't give up if your first attempts are not perfect. You'll get better. The bottom of the horizontal stabilizor is a good place to experiment.

BTW, I have a cheap Husky gravity feed gun, and I am using about 20 PSI at the compressor. I adjust the gun until it seems to work right. Can't tell you what the pressure is at the gun, but I would say 80PSI is way too high.

Tracy.
 
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Nice Paint Job!

freegespeed said:
These are some quick digital snaps of my RV6A. Of course there are plenty of little flaws in my paint job, but not enough to diminish the overall nice look and finish of it. I saved tons of money and learned allot about spray painting.

http://pg.photos.yahoo.com/ph/[email protected]/my_photos
Click to expand...
I'm planning to paint my own 7A with AFS so I'm glad to see you were able to do such a great job yourself! I'll be re-reading this thread when the time comes...

Dennis Glaeser
7A - fuselage kit coming in a week or so...
 
Time it took to paint my RV

Well this is related to the thread, but is more on a tangent, so I'll be brief.

I believe it took me 3 1/2 months of real work days spread over 10 months of total time. I had some gaps in the painting process. I was not originally planning to go back for more striping additions or new color choices at all. At some point I just made up my mind that I was going to paint on it again.

When I designed my paint scheme I was so worried about being too bold and gaudy, that I went over-board on the conservative side. After I went to some air shows and saw other painted RV's, the gears started turning in my head in terms of new designs. I now think that I would go pretty bold next time right out the get go in terms of color and design.

What colors are you using Tracy? I'm just curious.
 
Clark,

Two years ago, I bought a quart each of White, Metalic Red, and Metalic Blue. The white is all gone, and the red and blue are hardly touched, with the HS tips red, the top of the HS white, and the bottom of the HS blue. I'll probably carry over the bottom blue to the bottom of the wings, and paint the whole plane white with a few red (and maybe blue) stripes. The metalic red is really nice, and the metalic blue looks good, but I think I prefer their dark blue, like Andy Karmy used on his fiberglass.

I have done a gazillion different schemes and have pretty much decided to go with something simple. This is my first paintjob, and I figure the more complex the scheme, the more likely it will be for me to screw it up. I think I'll steal Mel's design, with the small star up front trailing two tapered stripes.

Tracy.
 
Tracy,

I wouldn't be afraid of using too much color. One thing I found after adding more color designs to my plane, was that the little flaws in my juno white base coat became less noticable. The eye looks more at the trim design then the under top coat. I would probably do a bright red and white split-down-the-middle scheme of some kind next time... (if there is a next time)..

The metallic blue looks really sparkly and shinny. I was told that spraying the metallic paints was difficult, but that wasn't the case for me. I did notice that the mixing faze took a little longer to get it homogenized. I would like to see a metallic red. That's a hot color I'll bet.

I also like the grays for transition between bright colors. You might think about that.

good luck, Clark
 
Thanks to all that replied, It seem I am on better terms with this painting process. First of all I moved the final pressure regulator to ON the gun rather than close to the gun. This allowed for 20 psi at the heel of the gun with a more reasonable 45 psi line pressure. Other changes were: 1) Change the spray pattern to a thin oval from a fat oval. 2) Close the fluid adjustment about 50%. 3)Reduce the paint a little more, 18 sec from 20 sec. 4)These changed allowed me to get a little closer and move a little slower.

I can now APPLY paint and watch it flow rather than flinging it. With some more practice and a little luck (and some 1500 grit and a buffer) hopefully it'll look as good as Clarks!

Paul Danclovic
Carver, Minnesota
8A Applying paint
 
About buffing AFS paints

I just thought I'd add a little info about my wet sanding/buffing experience on certain parts of my plane. The good news is that it does work. (with tons of elbow grease). This is a single stage (non-basecoat/clearcoat) paint, which experts don't usually recommend buffing on, but I think it worked for me.

The top of cowl had some sandy looking areas in it, so on a whim (I was doubtful it would work) I gave buffing a shot. I first tried a small area as the test zone, and to my surprise, it started looking smooth and glossy in that area. I then worked the rest of the top of the cowl and liked what I saw, but I new it wasn't as good as it could have been. Any way to make a long story short, I went back a couple more times trying to get rid of smaller and smaller scratches in the paint, until I was happy with the look of it. As far as the long term goes, it hasn't lost any shine since I did the work on it, which is now at least five months.

There were some mistakes I made and learned from doing the buffing as well. I buffed few areas down to metal, which were mostly very thin lines where skins overlap. (The area around the oil filler door is particurly vulnerable to this kind of mistake). RV's skins are flush rivited, so buffing down to metal shouldn't be a problem if you're careful. I also let the buffer get away from me once, leaving a small ding in an upper fuselage skin. I filled it in and repainted it, which made it almost invisible, but that really ticked me off! (no one to blame but my self!!!) Be careful with a high speed buffer in tight spots, or next to antennas!

Another thing I think is important to mention is that the specular gloss in the color sanded areas ended up slightly less glossy then the un-buffed, but properly painted sections of my plane. It still looks nice, but just not quite as glossy. I have a mostly an un-buffed plane that needs nothing more then washing and waxing to keep it up. I doubt I would buff my whole plane, only the problem areas.

My experiment did show that color sanding and buffing worked for improving a low gloss top coat finish..

I used a Harbor Freight high speed buffer (cheap and works good), 1200,1500,and 2000 grit wet sand paper, and the 3M Perfect It series of compounds for buffing and polishing.

good luck
 
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Sounds like all went pretty well. To those who will be buffing, it's a real good idea to put tape along all surface edges (maybe about 1/4 inch in) to avoid going through the paint. The stuff is unbelievably thin along edges and corners. Also, the longer you wait on modern paints the harder they get to buff. After about a week it gets real tough.
 
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