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Spray Gun Spitting


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So I am trying to spray deep blue metallic duplicolor paint shop lacquer on my current build, and I can't figure out how to keep it from giving me one or two little spits, which then mean I have to wet sand the whole thing due to it being metallic and a finicky beast. I am using HF HVLP guns, the 20 oz and the 4 oz. I sprayed the 4 oz at about 30 psi and the 20 oz at about 40 psi, but both give me the same issue. I have tried material feed rate changes, I've tried thinning the finish, but to no avail. I have also tried spraying a mist coat of acetone after the color coat, also a no go.

I am by no means a finishing expert, so if anyone has any advice I would love to hear it. Thanks.

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First thing that stands out to me is you said "Metallic".

What size tip are you using? What size metallic flake are you using?

Can you see where I'm going with that?

It could be a damaged tip/damaged needle, could be technique, could be the paint mixture, could be the tip isnt big enough for the metallic

When is it spitting?

Is it at the start of your run?

Also, when you say you're spraying at 30psi, is that at the compressor or at the gun? If its the compressor, then at the gun is probably more like 15psi and even though you think its spraying it, it's more like falling out. Must always have a variable guage at the gun

Heres a short video I did a couple years ago for some other members and covers a few things that may help

https://www.youtube.com/watch?v=eWQmZwQL2ik

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The nozzle sizes I tried were 1.2 and 1.5 mm. The can recommended a 1.4. I have seen your video before, very good, by the way! I am wondering if I need to run the finish through some cheese cloth or something, as I sprayed the first coats of this finish last October, but the weather hasn't been nice enough until this week to conitnue. I wonder if maybe there are little bits of partially dried finish that are getting in there. They look kind of like dust nibs, but they aren't. Over the course of the whole body, I get maybe a dozen of these guys.

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I wouldn't be spraying largea metallic through such fine tips, but it depends how fine the metallic is, for example I have fine metallics here that I spray through a 1.4 but most I use a 1.8 or larger.

Does your gun clog up a bit when its spluttering?

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The metallic is really fine, almost like a pearl powder. I have looked at the tip and it does not seem to clog. I'm not getting a spluttering pattern, just a random nib or blob or every now and again, and it makes it so I have to go back and sand and respray. I'm now on round 4 or 5. I'll see if I can get a picture of it this evening, as the spitting just looks like an island in an otherwise fairly smooth coat.

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Could be an air pressure thing

You never really answered if you have a gauge at the gun. Also, make sure that the cap and everything is tight and the seals are sealing properly as this can create issues as well.

I know my iwata airbrush is a real bitch with splutter when the rubber o ring at the cap needs replacing.

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alright, so I think I found something that works. I bought a new regulator for my larger compressor, set working pressure to 55 psi. Then, I double strained the finish, which removed some of the nastiness. This made it so that I only had one of the "spits" which seems to be debris in the finish. The coat I laid down tonight looks much better, but will need that one piece of debri removed, but I think I found the winning combination.

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I dont want to sound like a broken record, but you have still not said if your pressure reading is "at the gun"

55psi at the air compressor may still only be 10 at the gun if your line has average leaks or a long hose etc. I know that if I run one of my crap hoses that I need to have 90psi at the compressor to get 30 at the gun... I usually just keep my compressor at 120 or 130 and make my adjustments at the guage attached to my gun to get it exact.

If you're not getting the right air pressure at the gun then it can make the world of difference to the spray job, that includes not having the gun setup right. Some guns have a air pressure restrictor/adjustor on them and people often wind them in to make up for bad technique, but what youre doing is dropping the air prssure, if your gun has one of these (usually underneath), open it up. Most of the time people wind this in because a true 30psi scares a beginner sprayer and they get runs all over the place. The trick - move faster.

If you dont have a guage on your gun, then get one. They're not expensive, you can put fittings on it so you can swap it from gun to gun. It may be something that simple that is your problem.

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Also, yes, if you strain the paint then there should be less crap in it to blow out. Another thing is, sometimes if the gun is not cleaned proper, little bits of paint can dry up in parts of the gun,cap, cup etc and when youre spraying, get freed up and then become shite in your paint job.

I know I'm guilty of occasionally not cleaning my gun properly and its bit me on the arse before with getting flakes of another color in a fresh paint job.

It helps to dissassemble the gun if its filthy and let it soak in thinners overnight (not the rubber seals if it has any) and then give it a really good clean out after that.

One tip, keep a pin handy when you're painting as sometimes you'll need to pick a bit of crap out of the surface when its wet before it dries in the finish.

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I don't have a gauge at the gun, though I got an extra gauge with the regulator I just got, so I can hook that up. I basing pressure on what the needle read at the compressor with the trigger depressed on the gun.

I like the pin idea, I'll have to use that. I've been cleaning the gun regularly and checking the nozzle for build up (haven't had any yet). I've been keeping my spraying sessions pretty short.

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I just typed "inline air gauge" into eBay and this is the first one on the list (just to show you what to get) they're light and not bulky and won't hinder your spraying. I have one on each of my main guns and then one with quick release fittings do I can use it on my other guns and air tools

http://bit.ly/1dsjHHp

You should be able to buy them from your local paint shop if they sell spray guns etc

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