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I'm wondering if there are major pitfalls to using my Iwata lS400(gold cap) for base and then switching the cap to the silver cap for the clear. I'm using prospray and SPI every thing else. I'm not in production and new to painting.
Thanks.
 

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Couple of things to take care of when switching materials when you only have one gun..First is to clean the gun really well after each use..that should be a given and then base and clear shoot a bit different so you need to readjust the gun for each material..The readjustment drill is why pros will have several guns each adjusted for the material used in each gun..That is a real time saver when you are trying to make bank in a collision shop..

Sam
 

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Brian Martin,Freelance adviser
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Painted for years, never had dedicated guns, why? As long as the cap is the right size for both products, you clean the gun properly and there is no problem. Heck, in my opinion the time spent cleaning the gun of paint before clear is perfect because it keeps me from pushing the flash time on the paint. :D

But it's all about what you feel you need. I use to visit a shop up in Fort Bragg Ca who had a gun for each color, NO KIDDING! I wish I would have had a nice digital camera like I carry around now I probably would have snapped a photo. But honestly, he had about 25 or so guns. One for black, one for charcoal, dark blue, light blue, dark metallic blue, light metallic blue, silver, etc, you get the idea. He also put tape over the end of the hose nipple on the gun so nothing could go up in there. :rolleyes: He did NOTHING in the booth but spray paint, no masking, NEVER touching a car with sand paper or anything other thane PAINTING. Do you know what this nut job over the top crazy stuff got him? Some of the best out of the gun paint work I have ever seen. He VERY rarely buffed anything, they were REALLY clean and flat.

But me, nope, one gun and clean it and hit the car with sand paper and buffer most every time like most of the shops across America. Well I am exaggerating on the one gun, many shops do have a dedicated clear gun.

Brian
 

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If you use one gun you will learn the feel of it as you go from primer to base to clear and as a result get 3 times the practice per project...

It's not the gun but viscosity that needs to be changed..

Especialy when new to the paint game:thumbup:

 

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If you use one gun you will learn the feel of it as you go from primer to base to clear and as a result get 3 times the practice per project...

It's not the gun but viscosity that needs to be changed..

Especialy when new to the paint game:thumbup:

Very interesting methodology. Thanks for taking the time to share your experience.
 

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Great video

what is a good gun to buy for an occasional paint job Milo?
Assume a 1.4 tip to use, Ive got a
I've used Harbor freight stuff thus far and they work pretty good.
Thanks and I'll be back
walt
 

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Brian Martin,Freelance adviser
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Ok, no video sorry, but if there is one thing I learned as a paint rep and seeing what happens when you change mixing ratios is to follow the tech sheet to a T. Sure you can adjust a little, you are doing it a little.

But as a general rule.......

The mixing ratio should never be changed, the fluid adjustment should.

In seeing many different failures over the time as a rep, being called out to shops for trouble shooting being told by the shop that the product failed, I saw it over and over and over, there is nothing not one single reason for failure more than trapped solvents, not one thing more. It is the most common error found, too much solvents added, or not flashing off enough to allow what is in the film to escape. And if MORE is added, well, that adds to the problem of not enough time to escape.


During these five years I spent as a rep I learned a hell of a lot more than the twenty years I painted learning from my mistakes, why because I got to learn from the mistakes of painters all over my territory of 77 stores I serviced. The one most important lesson I learned was to FOLLOW THE TECH SHEETS!

If you think about it, a paint tech rep goes into the shop with his gun and shoots a demo, there is no time more important than this to shoot a nice job. his job is riding on this. The only reason he is there is to show the shop owner how great his paint looks and to SELL the shop on switching over to his companies paint. It could mean 15-20 thousand dollars in sales a month if he "lands" this shop, it BETTER look good. The tech rep will go into a shop with a van with a mixing machine with the stock of clear and harders and primers basically a "paint store" on wheels. He pulls in to that shop and shoots cars for a few days. He shoots all the customers cars with the painters help of course, for a couple of days. Can he teach the painters in that shop to do what ever they want with the paint? NO of course not, he has to shoot EXACTLY as the tech sheet says. Believe me, there is no ifs ands or buts, you shoot it EXACTLY as it says. The entire shop is examining your work on these cars, the owner has examined the finished product with a fine tooth comb. It had better look good, and it usually does, and it was all done EXACTLY as the tech sheet says. Why change anything when these come out so nice, setting up the gun is the most important part.



"Basics of Basics" Atomization and gun set up.
By Brian Martin

Being HVLP and low VOC products are the way the industry’s going I will be referring to them in this discussion on painting and paint guns. Most all basic issues dealing with HVLP can be applied to conventional guns, atomization is atomization. The HVLP just arrives at it differently.

The object of the spray gun is to break up the primer/sealer/paint/clear (I will call this “PSPC” from here out) into small particles and lay them in neat little rows on the panel being PSPRed. So the whole outcome rests on how well the gun is doing this. Picture the droplets of PSPC coming out of the fluid tip of the gun and then the air “slapping” them into smaller droplets.

You have two things that help you with this process, air and solvent. Solvent can mean something that is already in the PSPR from the manufacture or something the manufacture has told you to add to it. By the way, you should always mix in proper ratios as instructed in the tech sheet. The thinner (less viscosity) you get the PSPR or the more air you have at the fluid tip of the gun the more it will break up the PSPR. The target for you is getting the perfect balance needed. Too much solvent and the PSPR will have no body, fill, durability, etc. Too much air and you blow the PSPR everywhere but the car, poor adhesion, excessive texture, etc.

So, the answer is proper air supply and gun (and fluid tip) choice and how you adjust it.

With today’s high solids-low VOC (Volatile Organic Compound, you know the bad stuff that goes up into the air we breathe) products there is less solvent. And with HVLP guns there is less air at the cap to break up the PSPC, proper air supply and gun setup is more important than ever.

FIRST THINGS FIRST, your compressor and air supply.

An HVLP gun requires more VOLUME of air to operate (the V in HVLP, High Volume Low Pressure). Now you may notice that your HVLP gun is adjusted at maybe the same PSI as an old conventional gun, around 50 lbs at the gun (many HVLP guns are set at much lower though) so where is the “Low” in PSI they are talking about? It is at the actual air cap where the air and paint come out. An HVLP gun has only 10 lbs at the cap while a conventional has upwards of 50! So the VOLUME of air (CFM, Cubic Feet per Minute) is the key to proper atomization with an HVLP.

This 10 lbs I am mentioning is AT THE CAP where the air and paint comes out. It is not measurable without a special air cap that has a gauge built in to it. This air cap costs about $150.00 (and you would need a different one for every brand and model of gun you use) and is not needed to set up or tune your gun. Just looking at the droplet patterns will tell you everything you need. I only refer to it to make a point about HVLP operation.

If you have a gun that requires 15 CFM you will need a compressor and plumbing that will produce that at a very minimum. There are HVLP guns that need as little as 7.5 CFM so you can get good results even from a smaller compressor. Air supply is a complete subject by it’s self so lets assume that you have the air supply needed and move on to gun set up.

So atomization is the key, but why? Why can’t you just lay it out wet and let it “flow”, as an old painter will say. Picture a jar full of bb’s, they will represent well small, atomized droplets of PSPC. The gaps in between the bb’s is solvent. Now picture a jar filled with marbles, they will represent large, poorly atomized droplets of PSPC. The gaps in between are, you guessed it, solvent.

If you apply your PSPC in large poorly atomized droplets, what you will have is a film full of solvent. This can and will cause slow curing, shrinkage and dieback (the loss of gloss in the hours and days after application).

So, now that we have learned the need for gun set up, how do we do it? Lets start with the fluid tip choice. The newer high solids low VOC PSPC products need to be broken up more, so a smaller fluid tip is needed.
Basically you want the smallest fluid tip that will still allow you to PSPC the particular part you are PSPCing keeping the entire thing wet and in a fair amount of time. In other words a 1.0 tip would be beautiful for clearing one fender, but would be lousy to paint a complete. The application would be way to slow and the first panel would be way to flashed by the time you got around back to it. So you need to compromise, a 1.3 is a great all around tip, while a 1.5 though getting a little big, can get you by. If you read the tech sheet on the particular product you are shooting, it will have a recommendation for fluid tip size.
There are needs for other tips, for instance when shooting polyester primer you may need as big as a 2.3, but for urethanes and epoxies, the 1.3 or 1.4 will work great. If you plan on using a pressure pot or paint a bus, all bets are off and we would need to study a little bit more.

As an example of the use of a 1.3 tip I did a test once that proved the point well. I shot two panels of metal with a med solids urethane primer. One was shot with a 1.3 super high atomizing top of the line topcoat gun. The other was shot with a 1.5 (or a 1.7 I can’t remember) “hoser” primer gun. Three coats were applied and after a full cure (the one shot with the larger gun took MUCH longer to flash and cure by the way) the film thickness was measured. The one shot with the 1.3 tip was 2 tenths of a MIL thicker! The larger gun laid out the marble sized droplets full of solvent and when the solvent flashed the film shrank.

Air supply is a subject that could fill many pages by it’s self. So we are going to assume you have that covered and move on to gun set up.

You need to “tune” your gun EVERY TIME you use it just as you would tune a guitar before you perform. This is done with a very basic spray out pattern test. This very basic test tells you how your gun is atomizing and you adjust it to achieve the best atomization you can.

Lets do a spray pattern test:

Set the fan width as need (you don’t want to change it after you have “tuned” the gun). Turn out the material knob about 2 ½ turns. This is the “mixture” adjustment, kind of like the idle screw on a carburetor. The farther in it is screwed the lower the fluid to air ratio is and the smaller the droplets will be. The farther out it is, the higher the fluid to air ratio is and the larger the droplets.
Set the air pressure at the inlet to the gun to the manufactures specs. On an HVLP gun this spec is usually found on the gun and is the maximum PSI it can have while still maintaining the maximum 10 lb at the cap for legal HVLP transfer efficiency (68 %). You are now ready to do a test spray out.

Tape a piece of masking paper on the wall for the test. Hold the gun at a right angle to the wall, just as if you were going the wall. Hold the gun at a spread out hands distance (about 8” or 22cm). Pull the trigger to completely open for a split second and then close it. You want an ON-OFF wide open-completely closed in ONE movement. You should have a cigar shaped pattern with complete coverage in the center with fading coverage going away from the full coverage cigar shape in the center. The center should be fully covered without any runs. If you have runs, either you are holding the trigger too long, you are too close or the gun is simply applying too much material. In which case you need to screw in the material knob or turn the air pressure down. But most likely if you have turned the material knob out the 2 ½ turns and the air is set at the factory specs, you are just too close or holding the trigger open too long.

The droplets you see trailing off the center are what you will use to “tune” your gun.

Turn in the material knob to make the droplets smaller (and or raise the air pressure). The balance you need to attain is the smallest droplet size possible before you loose the coverage desired. In other words if you turn in the material knob too far, not enough material will be coming out to cover the panel!

Now, you’ll notice that I said, “raise the pressure to the gun”, while earlier I said to set it to manufactures specs. We are talking a very small adjustment. It is a fine balance in material to air ratio and a little more air than specified is okay. Even if it is an HVLP gun the inlet pressure recommended is to maintain the 10 lb limit at the cap. Well, about three quarters of the country has no regulations for HVLP use so if you go over the 10 lbs all it will do is atomize the material a little better. You may loose a little of the benefits of HVLP though. But remember you have a lot of control with the material adjustment knob.

After you are happy with the droplet size, DON’T TOUCH THE FAN CONTROL. It will change the PSI at the cap and will change the atomization you worked hard to get.
Do this spray out every time you spray as material change, temp, and humidity will necessitate a spray out droplet pattern test. Good luck!

The spray out patterns I used to show are long gone being I uploaded them on a web space I no longer have access to so I stole this one from someone.



So there you have it, a couple of different looks at using the same gun for two different products. I do have a dedicated primer gun, as that ones fluid tip is a little larger at 1.7 (as I remember) and my painting and clearing guns (I have two depending on my mood which one I use) one has a 1.3 tip (Sharpe Platinum, I LOVE that gun) the other has a 1.5 tip (Devilbiss). So shooting a paint and clear with the 1.3 or 1.5 is perfectly normal because both would require in their tech sheets a 1.3 or 1.5 tip (at least the products I have used). So they shoot just fine either product paint or clear following the exact mixing ratio in the tech sheets.

Brian
 

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what is a good gun to buy for an occasional paint job Milo?
Assume a 1.4 tip to use, Ive got a
I've used Harbor freight stuff thus far and they work pretty good.
Thanks and I'll be back
walt
Yes your 1.4 is a good all round tip size.. You are on the right path..
 
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