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Paint spray technique?
Paint spray technique?
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Old 14th January 2018, 12:09 AM   #1
Dave Zan is offline Dave Zan  Australia
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Default Paint spray technique?

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
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Old 14th January 2018, 12:28 AM   #2
jplesset is offline jplesset  United States
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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.
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Old 14th January 2018, 05:01 AM   #3
Dave Zan is offline Dave Zan  Australia
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Originally Posted by jplesset View Post
...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
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Old 14th January 2018, 05:33 AM   #4
metalman is offline metalman  Canada
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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.
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Old 14th January 2018, 10:36 AM   #5
Dave Zan is offline Dave Zan  Australia
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Originally Posted by metalman View Post
...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

Last edited by Dave Zan; 14th January 2018 at 10:44 AM.
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Old 15th January 2018, 10:15 PM   #6
chrisb is online now chrisb
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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.
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Old 15th January 2018, 11:35 PM   #7
Dave Zan is offline Dave Zan  Australia
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Originally Posted by chrisb View Post
...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
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Old 16th January 2018, 02:20 AM   #8
PRR is offline PRR  United States
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Quote:
Originally Posted by Dave Zan View Post
...copy of the Star S2....
That's a touch-up gun, for fixing a scratch on your car.

For whole fenders, or speakers, or panels, I think you just need a bigger gun.
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Old 16th January 2018, 05:15 AM   #9
Dave Zan is offline Dave Zan  Australia
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Originally Posted by PRR View Post
...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
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Old 16th January 2018, 07:02 PM   #10
chrisb is online now chrisb
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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.
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