I am new to bodywork and trying to learn for a Bugeye restoration project. I am fixing a fender on my truck to get experience.
I have a Harbor Freight 66222 HVLP gun. This is suppose to be the good one. From what I have read the pressure should be set with the trigger pulled. What is surprising to me is I have to have almost 80 psi of static pressure to get about 35 psi with the trigger pulled. These values are coming from the regulator that comes with the gun, attached to the gun.
My air line setup is almost 50' of 3/4" copper after the tank, then a regulator on the wall ( Maxline 3/4" ) and then 50' of 1/2" flexible line to the gun. The only quick connect is at the gun. I have a Devilbiss inline filter screwed into the pressure regulator at the gun.
Does it seem right to have to have that high of a static pressure at the gun? It concerns me since the instructions for the gun say something like 60 psi max.
I don't really know what to look for in gun pattern to tell if the pressure setting is good or not. I was surprised how hard the gun blows at the masking. Some of my cheap paper grocery bags with green hardware store painters tape masking blew off.
Practice on something big and flat and preferably vertical. Paper or cardboard taped to the shop wall, whatever. Load the gun with thinner only and play with all the settings until it shoots smooth and uniform and how you want. There's got to be a youtube on it.
Yes, that static pressure at the gun is fine. 35lbs with a pulled trigger sounds high, but the guns specs will tell you what it should be. The pressure at the cap should be about 10 lbs, but, with a lot of guns they'll just give you an input pressure and tell you that the air cap pressure will follow. There are air cap gauges, but you don't really need one.
FWIW, my Devilbiss specs 23 lbs input to get 10 lbs at the cap. My HF gun (may not be the same one) says input between 30-40 lbs with max of 40 (which HAS to be with trigger pulled). It doesn't say what the cap pressure would be, but it should also be around 10 lbs, though a bit more than this wouldn't be a problem.
Whatever you do, consider the air pressure an initial setting. You're going to have to tune your spray using your material knob and maybe the air pressure to get the optimal amotization and coverage. Here is a good basic explanation:
http://www.stovebolt.com/techtips/hvlp_paintgun_basics.htm
BTW, if you are checking pressure with an empty gun and blowing 100% air at your masking then you'll find it acts a very differently with material in the gun.
Well apparently I've been doing it wrong then.
Thanks for the comments. I was going for 40-45 psi based on this post https://grassrootsmotorsports.com/forum/grm/massive-orange-peel/32344/page1/
I started out spraying a big piece of cardboard, but was having a hard time making heads or tails of what was good and bad. I think a lot of the problem was spraying on cardboard. The paint seemed to be reacting a bit funny to it.
I sprayed clear today and had some problems with runs. I was trying a lower pressure at the gun for the first coat. It is my understanding too low of a pressure can contribute to runs. It looked OK on the cardbaord before, but not on the fender I was painting.
It still seems odd I am getting so much pressure drop through my air line system. Maybe my regulator on the wall is bad. This makes me wonder how much pressure I am actually getting at my impact guns when I am trying to break something free,
