I have found a pro to paint my car, but I am doing the body work and prep myself. I understand that (as with a lot of things), a paint job will only last and look good as long as the base is solid. I am using etch primer, followed by 2k Urethane. My cheepo Harbor Freight gun is very hard to use and seems to leave a very rough surface after the primer has dried. Does the quality of the gun in respect to atomization, etc, affect the bonding and durability of the primer? So far I've only done one door, but am getting ready to do the fenders and am concerned that even though I am prepping properly, the quality of the primer application will affect me down the road. Any opinions. Thanks again! graemlins/beers.gif

what gun are you currntly using? Siphon, gravity or pressure feed? What size fluid tip? At what pressure are you spraying at? What primer?

It could be a number of things causing the roughness in your primer, primers usually don't require a high dollar gun for acceptable application results. Sometimes orifice size/fluid tip is often to small for the high solid materials.

The air compressor you are using is another factor. If you dont have the proper air(CFM) for a paint gun to operate properly, NO paint gun will work be it a 500 dollar Sata or a 49.99 Sears special.

And as Bob mentioned we need more info graemlins/beers.gif ...Eric

I am using Sherwin-Williams GB-980 Etch and P-50 Ultra Fill II 2K Urethane-Acrylic primer. I have been mixing the primer for normal build. The gun is a standard siphon feed, Nozzle size says it's 0.082", it has no mention of needle size nor could I find any markings on the needle itself. I set the compressor to around 32 psi based on the product data sheet. I set the gun up the best I could using the "Basics of Basics", but it seems that the material knob is now screwed all the way out. The CFM requiments for the gun says 6. I have a Coleman 5 h.p compressor with a 20 gal tank, which is the whole reason I bought this gun because I knew my compressor wouldn't run anything else other than a mini-hvlp touch-up gun.

The gun reminds me of a lot of the "hot rods" my friends had in High School....Makes a lot of noise, but doesn't do much.

I have no problem changing guns if I have too, but the cost of a new compressor added to the price of the gun= 2 qtr panels.

Thanks for the help guys. Hope I gave enough info. graemlins/thumbsup.gif

You mentioned the air pressure was set at the compressor. It should be set at the gun, controlled by an air regular with a dial gauge.
That is the ONLY true way to measure the psi going to the gun.

Am not 100% sure on my numbers but I think that for every 15ft of pipe/hose you lose 10psi. Of course hose size changes that number, but still you lose psi over a length of piping, making that psi gauge at the gun even more needed.

Also pretty much all standard siphon NON HVLP guns run in the 50psi range to work properly...Eric

Something else I noticed was the nozzle size of .082.
Using a metric to decimal chart a 1.8mm tip equals out to .0709
Your tip equals out to 1.9mm which is rather large for that 980 and P50. Trying to remember what S-W says, 980 needs something in the 1.4 range and P-50 is up to 1.6 if I recall right.

Thanks for the info. I have 50ft of 3/8 line so I'm probably losing quite a bit of psi. Looks like I'll look for a different gun then. What a waste of $14.99. :D I guess my wife could use it to water plants or something.

7DSS,
Before you throw it out try those few things first. Readjust the air pressure, buy an air regular for the gun. They are pretty cheap Sharp makes some in the 20 dollar range, plus they can be swapped from gun to gun.

Also check the "ID" or inside diameter of your hose. Even thou its not an HVLP, 3/8ID hose is needed for HVLP.

I did happen to find my air pressure drop chart.

At 40psi with a 1/4ID hose running 50ft you lose 16.0psi
5/16ID hose at40psi 50ft is 4.0psi loss
3/8ID hose at40psi 50ft is 3.5psi loss

Now crank up the pressure to 80psi you lose
25psi with a 1/4id hose at 50 ft
8.0psi with 5/16 hose at 50 ft
6.0psi with 3/8 hose at 50 ft

SO you see having the correct ID of hose can really make a huge difference...Eric

Eric, using my conversion chart (I can't for the life of me learn the formula to do it myself smile.gif ) that is over 2.0!

Yep, that is a big gun.

7D, loose a bunch of that "line" (I assume you are talking hose), unless your compressor HAS to be that far from your work area, bring it down to about 25 ft to start. Next, as Eric mentioned, you REALLY need to bump up the pressure. If you set your regulator at the compressor at 32 lbs you had about 20 at the gun, that is just not going to work. What you need is to remove the reg at the compressor (you just don't have enough compressor to need it) and put an inline reg at the gun. THAT one at the gun should be a 30-35. I know that tech sheet says 30-35 lbs and I am sure it will work just fine there but I don't remember ever setting it there. I just adjust the gun to make it work smile.gif

Do you still think my nozzle size is too big though? I will get the regulator and guage for the gun...makes sense. I seriously doubt I can find replacement nozzles for this "high-end" gun, so should I go ahead and look for another gun with the 1.4-1.6 nozzle size? Thanks again, as always, much appreciated.

Yeah 70D, that tip is just so big I don't think you should try to "choke" it down with your material knob, though you could try. The thing is it just doesn't break up the material enough and can leave you with trapped solvent in your film.

Thanks guys. graemlins/thumbsup.gif

7D sounds like youre makin some progress! smile.gif i need to get out there and check it out. I just paid off my short block, gonna set the motor and tranny in soon. Good luck on shootin primer

Anthony,

Thought you dropped of the face of the earth or something! Probably been extremely busy like me. It may sound like I'm making progress, but I've got a loooonngg way to go. Doing a panel at a time, and with my schedule and "blazing" body work abilities.....Well you know. Let me know if you need help dripping in that motor. graemlins/thumbsup.gif

yeah work has picked up now that the weather is warm again, this week was slow due to the rain. Plus i havent had much money to throw at the car lately. I did finally get the short block paid off though. Will probably pick it up monday and put the flywheel clutch and tranny and set it in. wont be starting it anytime soon though, still gotta get the heads finished, one thing at a time..... Ill give ya a call if i need some help, im still anxious to take a look at yours.