I recently puchased an HVLP conversion gun from Porter-Cable, which I believe is actually a DeVillbis gun, since P-C bought them a few years ago. I have a smallish compressor, but this gun is supposes to operate at 30-35 lbs. I spray lacquer, both solvent and waterbased, usually satin finish. I am convinced that lacquer is the best finish for furniture that is going to be used and not just looked at. My problem is that I have trouble getting a “wet” coat on the surface. It typically is more of a dry, grainy type of coating. The gun is thoroughly cleaned after every use.
I could use some help with the following:
1. Initial adjustment of the air, liquid, and fan valves. The gun came with basically zero instructions.
2. Viscosity of the finish out of the can. They are both labelled “ready to shoot”. I have used Oxford’s Premium Water-based lacquer, and Behlen’s pre-catalyzed nitrocellulose lacquer. I believe these to be very high quality finishes. Should I be thinning them instead of using straight from the can?
3. Should I have a particular needle/nozzle size? I only have the standard one.
4. Should I scrap the above and get a turbine setup?
Any feedback on the above is much appreciated, along with any recommendations. I am willing to do whatever is required to get a quality result.
Edited 9/2/2005 4:42 pm ET by quartersawn
Replies
The first thing I'd suspect is your compressor. The PC spray gun needs 9 CFM to spray well and it takes a good size compressor to supply that much air. It does spray nicely when everything is balanced (e.g., CFM, viscosity, and gun settings).
If it's the gravity fed gun, thin the finish until a stream of fluid comes out of the nozzle when you pull the trigger without the air connected. The stream can drop right off as it comes out of the nozzle.
Keep than fan narrow (~4") at first with the fluid knob open most of the way and increase the air pressure until it atomizes well. Spray test stripes on scrap or cardboard and overlap each pass to maintain your wet edge. If you want to experiment, widen the fan and increase the air until you reach a point where you lose a solid wet stripe or the overspray is too much. You can thin some more to get a wider fan at a lower air pressure. It's okay to thin the Target water-base up to 50%, though 15% - 20% should be fine. Same for the pre-cat.
Paul
http://www.finishwiz.com
Thank you for the information and the trouble to check for the specs, etc. If my compressor can deliver 6.5 CFM at 60 lbs, and my HVLP gun requires 8.5 cfm at 40 at 40 lbs, is this a mis-match that prevents my gun from performing? I should add that I have a standard type gravity feed Porter-Cable touch-up gun that requires only 3.6 cfm at 60 lbs. Perhaps I should use that and just put up with the extra overspray and be sure that I have a well ventilated area. What do you think?
Sounds like the compressor is pretty close - the CFM goes up as the pressure (PSI) comes down. The compressor may run a lot once the pressure in the tank gets low, but you should still be able to spray. You may see the gun slow down if the compressor gets behind.Always use the lowest pressure possible to get good atomization (fine droplets). At the right settings, you shouldn't see a LOT of overspray even from a conventional gun (though you may have to move slower than usual).Paulhttp://www.finishwiz.com
I don't have the PC gun but I do use the Wagner conversion gun with a great deal of success using these basic settings. They may help you establish a starting point.
Set compressor at 25# and the gun @ 9psi. Open the airvalve to full (really not used) Turn material adjustment all the way closed until trigger won't pull, then pull trigger and begin to open material knob until the gun starts spraying. Adjust the fan width by turning the cap. From that starting point you'll need to adjust the gun pressure for best atomization and I usually wind up around 6-7 psi. Hopefully this will get you started and then just play with the settings.
Jon
Sorry forgot to mention I'm using the Hitachi 2 hp twin tank compressor and it does a good job keeping up.
Jon
About Devilbiss... Actually, according to their website... a few years ago Porter-Cable teamed up with a company called Devilbiss Air Power Company. That's a different company than the one that makes Devilbiss spray equipment. The Devilbiss spray equipment company is owned by ITW, which also owns Binks and Ransberg (powdercoat spray guns). Actually, I think they're owned by a division of ITW. It's hard to keep track these days. LOL
On the lacquers... I've never used water-based lacquer and really can't give you any informed feedback on that. But, I've been using a wide variety of solvent-based lacquers for several decades now. And I own and use several conversion HVLP gravity guns.
I'll ditto what Paul said with one caveat: I never use lacquer thinner. Instead I use a blend of MEK and PM Acetate and have for many years in a variety of commercial settings. Once I got turned onto the MEK/PMA blend I never wanted to go back to lacquer thinner.
Plug "MEK" into the Knots search form and you'll find several posts where I went into quite a bit of detail on how I use this blend as well as why I use it. I will just add here that this blend is also the only thing I use to reduce Acrylic lacquer (including automotive), CAB-Acrylic lacquer, regular nitro lacquer and most conversion varnishes.
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