I was watching a guy on American Hot Rod (?) last night and saw a professional painter spraying a 57 chevy with red (basecoat I assume). I noticed a large amount of overspray which indicated to me that his pressure was set higher than I would have expected. When I am spraying, I get very little overspray while shooting my basecoat and clearcoat, but I also am ending up with orange peel. I am setting my compressor on appox. 40psi when shooting. Do I need to turn up the pressure to achieve a finer atomization like that guy was obviously getting ? Does this sound like the cause for my orange peel ? Thanks as always graemlins/thumbsup.gif

Click here for the "Basics of Basics" to atomization (http://www.camaros.net/forum/ultimatebb.php?ubb=get_topic;f=3;t=002548)

CLick on the link above for some information on gun set up. As far as how much pressure, it depends on your gun. What brand is it?

The guy shooting on the show may not have been using an HVLP maybe?

Or he may have just upped the pressure to atomize better. Either because he didn't know how to set up the gun and choose the proper equipment, or just because it was needed after everything else was tried.

You need a good air volume to use an HVLP gun, what compressor , piping and hoses are you using?

Martinsr, I've been watching that same show. That was the third episode in which Boyd's shop is building a '56. Anyway, what is your opinion on chemical dipping. In the first episode they chemically dipped the complete body. I've been thinking of dipping my 70 body. Thanks for any advice.

Tim, am no fond of chemical striping. I have only did it with a few vintage Fords years ago so I don't have a lot of experiance though. This is the problem, EVERYTHING is removed. That means EVERY bit of primer, sealer, seamsealer, from the ENTIRE thing is removed. Much of these primers and sealers are very hard to replace being they are buried behind double panels and that sort of thing. If the body would then be "E" coated by dipping that would be ok I guess.

IF you set your pressure 40 at the compressor and you have 40ft.of hose isn't that going to lower the lbs. by the time it gets to the gun?
In Cal.Isn't it a law you must use a HVLP gun?And I think they have to use water base stuff too?
I have noticed that some painters like to mix there paint there Way.And if that guy mixes his thick then he would turn the pressure up alittle.
MARTINSR.Chime in here please.Thanks
-Kid

Hey guys that episode is on right now on the Discovery Chanel.
MARTINSR thanks for the response.

IF you set your pressure 40 at the compressor and you have 40ft.of hose isn't that going to lower the lbs. by the time it gets to the gun?
Yes!! not 100% sure on my numbers but I do believe that for every 25ft of hose you lose 10lbs

The point of mixing the paint or basecoat thicker is too provide greater coverage. You can mix it thicker on the first coats for coverage then mix it the normal way 1:1 for proper color. But this method is something that I DONT RECOMMEND

Originally posted by TonawandaKid:
IF you set your pressure 40 at the compressor and you have 40ft.of hose isn't that going to lower the lbs. by the time it gets to the gun?

As Eric said, that is very correct, you need to set your pressure AT the gun. The size of the hose, the amount of couplings, filters, etc. can ALL effect the air volume you get at the gun.

In Cal.Isn't it a law you must use a HVLP gun?And I think they have to use water base stuff too?

No, not at all. There are particular counties or parts of counties where HVLP is required just like some counties in other states. But much of California is under "National Rule" just like most of the country. And NO we are not using water borne paints or primers. There were some used before they caught up with the technology to make the urethane low enough in VOC. Now, everything is urethane to speak of.

I have noticed that some painters like to mix there paint there Way.And if that guy mixes his thick then he would turn the pressure up alittle.
MARTINSR.Chime in here please.Thanks
-Kid Your paints should be mixed as per tech sheet. Most basecoats are one to one as Eric said.

When setting the pressure at the gun, should you set it with the trigger of the gun depressed or not. (i.e. static or moving air when setting the gage)

Trooper

It should be set with the trigger pulled.

Well, just as I thought, you guys have come thru with flying colors. graemlins/thumbsup.gif When I sprayed my last test panel, I had the compressor gauge set to 40psi and now I know that was my mistake.
Kid, thanks for making this point ;)
Brian, I read your basics of basics on atomization and don't recall the pressure drop from compressor to gun being mentioned. All of your posts, as well as Eric's have always been extremely helpful and I appreciate them all.

As I suspected, it appears that low pressure at the gun was my problem, so last night I set my compressor to 60psi and figure I had about 45psi at the gun (after learning this today) and the atomization and pattern (fan) of the primer I was shooting appeared to be much better.

Brian, I am using a 20 gal, 4.5 HP Craftsman with a 3/8 hose, 50' long. The gun is a Husky HVLP from Home Depot that seems to be descent quality. I do have a moisture filter between the compressor and the hose and have never seen a drop of water in it :confused:

What psi do you think would be ideal for my PPG basecoat/clearcoat work ?

Thanks again for all the help, this all makes perfect sense. :D

Originally posted by Texas70:

I am using a 20 gal, 4.5 HP Craftsman with a 3/8 hose, 50' long. The gun is a Husky HVLP from Home Depot that seems to be descent quality. I do have a moisture filter between the compressor and the hose and have never seen a drop of water in it :confused:
John,
The most likely reason you are not seeing any moisture in the trap is because it does not have a chance to work and the water vapor is passing through it. For it to work you must use copper or black iron pipe, then place the water trap at least 25 ft. from the compressor. Are you using a pressure gauge on the gun also?, or are you guessing the pressure drop based on the lenght of hose? Check this out for shop piping: Shop piping (http://www.sharpe1.com/dr-pipe.htm)


Good luck,
Mike

Texas, the pressure of the gun is determined by the gun maker. Not all guns run at the same pressure. The three satas I use at work all run at different pressures. The LM2000 is set at 43psi, the JET B is around 45-50, the RP is 32psi, my NR2000 is at 29 psi.

Shrape's Cobalt and Titanium guns run at 50psi.

PPG rep gave me a Devilbiss JGA gun which I believe runs at 20-25psi.

So you see it all depends on your weapon of choice...Eric

I am fairly certain that Boyd painter knew what he was doing for adjusting his Sata guns.

BTW the Sharpe Titanium is listed for 30psi.

http://www.sharpe1.com/titanium.htm

Upping the pressure is a trick that works with HVLP to get better atomization. The only problem with HVLP for that trick is at a certain point the pattern will start to distort. It also raises the air cap pressure out of the 10 psi range which is a violation for HVLP required areas concerning Professionals.

Did anyone catch the part for the Junk Yard Dog getting 6 coats of the custom Boyd Red color available from DuPont?

Got to give the Boyd painter a thumbs up for wearing a Supplied Fresh Air System on TV.

Thanks again everybody for the links and info graemlins/thumbsup.gif . I will check, but I am pretty sure the directions for use with my Husky gun calls for 40-45 psi "at the gun", so I will get a gauge to attach at the gun and move my moisture filter upstream after reading the link provided above. I assume I have been running about 15+psi to low....could this be the cause of my orange peel, poor atomization ?