Paint spray technique?

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I have a small air gun, 0.5 mm nozzle.
It works fine on the detail work I have it for, mainly to spray paint equipment with tubular struts and similar parts.
I have tried to spray a few panels, 450 mm or so width, about the size of a typical speaker.
This was less successful - hard to blend the narrow spray passes, not helped by the fact I chose a metallic paint which adds the complication of texture to match.
I am not a very experienced spray painter and the 2K polyurethane is both expensive and toxic so I want to minimize the trial and error experiments.
I plan to thin the paint a little more than usual and work the gun a bit further away - should make a wider fan and blend better.
Perhaps increase the air pressure?
Obviously there are limits to how far I can push it, a step up in nozzle size would be better but it's a no-brand gun so probably no parts availability.

Anyone here have any expertise in this?

David
 
I'm still using the Binks 52 I bought 40 years ago. It's not a trim gun, but was state of the art when I got it for painting cars and such. It throws a fan about a foot wide (or tall, I mostly use it that way). For covering a large area, there really isn't a good substitute for the right tool.

Yes, I have used it for automotive poly, and yes, that stuff is crazy expensive. I paid on the order of $150 for a quart of metallic paint. For speakers, though, I would stick to interior latex or lacquer. I'm currently doing a pedestal, about the size of a big floor standing speaker in lacquer. Paid $45 for a gallon custom tinted to match the walls.

There are metallic interior latex paints that work quite well, and are inexpensive, too.
 
...For speakers...I would stick to interior latex or lacquer.

The panels are machinery rather than speakers, I just described them as "about the size of" speakers to provide a convenient comparison.
So I do need the polyurethane.
But I also wanted to try it as a test before I do speakers.
I really like the durability of polyurethane, I used it on my first serious speakers and it stood 30 years of parties, transport to friends' parties, multiple moves to different houses, interstate travel in removal vans, and the like.
Worth the expense, it's the toxicity that I find problematic.
On simple flat surfaces I would be tempted to use a roller, to avoid spray.
Unfortunately my machinery panels have tabs and bends that make this impractical.

Another gun with more capacity may be the simplest option.
Thanks for the comments.

Best wishes
David
 
With a mini gun the biggest trick is to get the passes to blend. The solution is to minimize how much air is going to the gun while still getting adequate atomization and fan shape. It takes a bit of experimentation / trial and error but can be made to work. Start with your gun set to a round pattern as opposed to a fan, and increase the airflow/pressure until you just reach a decent level of atomization. At that point, increase the airflow to to horns until you get a semiflat fan. Don’t try to get a fully flat fan! An elongated oval will do. Remember that you want to overlap each pass by half. I wouldn’t recommend thinning more than 10% if you can avoid it. Part of the problem is having excess air from the gun causing rapid solvent flash off.
 
...the passes to blend. The solution is to minimize how much air...

That's not what I expected, but I don't have a feel for all the interactions between air, paint and technique.
So I hadn't considered that excessive air would flash off the thinner.
I still think that I didn't have sufficient thinners last time.
That is based on the assumption that a 0.5 mm nozzle would need paint a little thinner than the usual mix typically intended for car painters' equipment, and the paint flow seemed too slow, which is independent of subsequent solvent evaporation.
So I will try to fix that first.
If necessary then I can experiment further based on your advice.
If that doesn't work then I can buy an additional gun with a wider fan for panels.
By that time I will have applied more coats of paint than a show-and-shine car fanatic
Thanks for the reminder to overlap my passes correctly.

Best wishes
David
 
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The cheapie ($40 -60) HVLP syphon and gravity feed guns we use in the shop allow for a pretty wide range of adjustment to fan pattern and air / material mix, so you may not need a separate / additional gun.

Not yet mentioned is keeping water out of compressor driven systems - this is particularly important for solvent based & catalyzed products. For those not working in a commercial setting with air dryers, there are in-line separators that work like a charm for this.
 
...adjustment to fan pattern and air / material mix, so you may not need a separate / additional gun...

What size guns are these?
Mine is a mini gun, gravity fed, more or less a copy of the Star S2.
As already mentioned the fluid nozzle is 0.5 mm which produces a maximum fan width of only about 75 mm.
I now suspect I was a bit optimistic in my expectations of such a small gun.

Best wishes
David
 
...for...a scratch on your car...

As already explained, I use it on machinery parts - the small fan is perfect for 25 mm to 50 mm tubes.
Obviously less than ideal for panels.
But I expect an experienced painter could do them, just rather slowly.
So if I can do this one-off job successfully then I will have learned some skills, in particular how to blend spray passes seamlessly.
That seems a useful ability to have, even if I buy another gun.

Best wishes
David
 
Dave - we use an array of air powered syphon and gravity feed guns for spraying lacquer, stain and paints. The syphon (pot) guns are 1 quart, the gravity feeds approx half that. Standard tip size is 1.8mm - by dialing the air pressure to around 40 psi, and adjusting material volume and spray fan width, we can get pretty decent coverage.
For large horizontal surfaces, we also use airless.
 
With a metallic, I have made the last coat almost all thinner to get all the metallic particles to lay down in the same direction or evenly.
Another trick to keep the paint from running or puddling is to spray a light tack coat at first. This can sit for about 5-10 minutes before putting on about three full wet coats. The paint should be just about the same viscosity of milk.
Test first or do some less critical parts before the important parts. The urethanes will flow out a bit after spraying for some time, so absolute gloss isn’t required.
I am still sensitized to a certain version of a Sherwinn Williams product, even after thirty years of not using it. Toxic is putting it mildly.
 
With a metallic, I have made the last coat almost all thinner to ...lay down in the same direction evenly...

Thanks, this confirms my idea that lower paint viscosity is the key.
Made it hard for myself with the worst possible combination, a small fan and metallic.
Still haven't done the last coat yet, partly because it's too hot, ~40 C, and partly in case there was further advice.
But there seems to be reasonable consistency of recommendations so I will do it soon.

Also just realized additional reasons polyurethane is perfect for speakers, it has the qualities that Nelson Pass identified for mythic audio components, it's both expensive and toxic;)

Best wishes
David
 
There are paint additives to slow evaporation and drying, that will make flow-out better. Floetrol is one I have used. Must be more careful not to spray too heavily, or it'll run/sag on you.

I like to spray horizontal surfaces, and let it dry, roll the cabinet, and spray more. Can't run then. Just be careful of overspray on the sprayed side.
 
If leaving a day or two in between coats, I have found it to be beneficial to very lightly sand the surface with 400, and use a bucket of water for lubricant with a couple drops of dish soap. A light wipe with an alcohol dampened rag, followed by a tack cloth will help the next layer flow out.

I wouldn’t do this before the clear coat however, just put that on right after the base has set up a bit.

Materials are so costly, I usually try and do a sample panel before the intended surfaces.
 
Do you have a viscosity cup to test your thinned paint?...

Yes I do.
It is a little tricky with 2 pack paint because, of course, it thickens even as it sits in the cup.
Because the 2k is expensive I first did a few tests with an enamel then tried to thin the 2k to the same viscosity.
I have seen it recommended to wait a while after the 2 components are mixed, perhaps there is an initial reaction that settles down, with only a slow increase in viscosity after that, or so it seemed.

Best wishes
David
 
There are paint additives... Floetrol is one I have used.

I know of these for conventional paints, I don't know how they would behave with a 2k polyurethane, they may even mess with the chemistry and I am reluctant to risk this.

I like to spray horizontal surfaces, and let it dry, roll the cabinet, and spray more. Can't run then. Just be careful of overspray on the sprayed side.

I tried to spray as much as possible horizontal but it's not just a simple box, it's a sort of tray stand with projections in the middle.
So it's mostly horizontal but when I spray the vertical bits I am stuck with some overspray. This didn't mess up the finish as much as I feared.

...I have found it to be beneficial to very lightly sand the surface with 400, and use a bucket of water for lubricant with a couple drops of dish soap...

I don't understand what you mean helps the next layer flow out, the fact that the surface is sanded or the dish soap or the alcohol?
I have to sand between coats to fix minor problems anyway, even it wasn't required to improve the adhesion of the next coat.
But I try to keep the surface perfectly clean, also to improve the bond.

Materials are so costly, I usually try and do a sample panel before the intended surfaces.

Materials are so costly that I can't afford to paint a sample panel;)
I try to do a sample on the bottom or back where the paint isn't wasted but the finish is less critical.

Thanks to everyone for the continued recommendations (previous post too, should have included both replies into one tidy post but ran out of time)
I think I may buy another spray gun for panels.
Can't decide between HVLP and conventional.
Despite all the claims, I have seen very little actual data to compare.
What are the actual structural differences? air cap hole sizes?

Best wishes
David
 
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The sanding is pretty much as you are already doing by just cleaning up the surface before the next coat. The tiny bit of soap helps with any potential tearing of the soft paint, and the alcohol removes any residue prior to painting.
Another trick is to cut a small radius on the sandpaper corners to prevent them from digging in while doing this.
Just keep that respirator on!
 
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