How to Set Up a Spray Gun
George VondriskaDescription
Master woodworker George Vondriska provides step-by-step instructions on how to set up a spray gun to optimize its performance for your woodworking projects. A WoodWorkers Guild of America (WWGOA) original video.
It's really important that, in order to get the most out of your spray gun, you know how to get it set up just right. It's really not that hard to do. So let me walk you through, step by step, the way to optimize the performance of a spray gun. I'm running the HVLP compressor based gun here, and what I'm going to do, is open up the fan control, and my fluid control, as open as they can be, and I want the widest fan possible, I want a lot of fluid coming out. As you back out the fluid control, make sure you don't get it out so far, that it comes completely out of the gun. We don't want that to happen, but it's going to be at a point where it's barely threaded into the gun at all. On the regulator, which I've already got hooked up down here, once I'm on air, this is going to be run at about 10 PSI, that's way too low for this gun, but that's how we want to get started. We want to start low, I'll show you what I'm looking for, when I spray on the rosin paper back here, and then, in tiny increments, we're gong to sneak up on exactly where the performance is perfect. Now, I'm going to spray right here on the paper, and what I'm looking for, is the drip pattern, boy, does that stink! I'm not atomizing at all, my pressure is really, really down, I'm just getting a splotch on there, so I'm going to increase pressure. That's so low, I'm going to go up 10 pounds. Now, as I look at these drips, what I'm looking at, is the uniformity of the drips coming down. I've got drips in the middle, I don't have a lot of drips down here, out here at the outside, so I'm not quite there yet. What I want, is a uniform pattern of these runs, coming down all the way across the width of the fan. So, I'm going to go up a couple more pounds, try a fresh piece... That's better, look at, I'm pushing drips out to the outside here, but they're not quite running down the paper yet. I'm going to go up five more pounds. What we want to do is, we want to sneak up on this from the bottom. You don't want to overshoot, you don't want to exceed your pressure. Real close, one more little bit and we're going to have her. Now we've got it. We're to a point where, look at all those drips, all the way across the width of that fan. Shooting this on this paper, makes it very obvious, that all the runs, are the same size, where from end of fan to end of fan, we got drips going all the way. So, now I can note where my regulator was set. Now that's going to be pertinent to this viscosity of liquid, so, I'm shooting water here, again, so I don't have to have a respirator on. When we change this to lacquer, or polyurethane, or shellac, I'll start with this experiment again, because the pressure might be a little bit different, for those products, but once you go through this procedure, you'll know exactly what the right pressure setting is, so that your gun sprays, as good as it possible can.
I disagree. For a gravity feed HVLP gun with a 1.4 tip, I know that I'll need 45 PSI. I use a different gun for each material depending on the cleaning agent. Shellac gets DNA, lacquer and real poly gets MS or lacquer thinner, and the so-called water based polyurethane, which is really acrylic, gets water. I never use the same gun that sprayed any colored material for spraying any type of varnish. You can't clean your gun out 100%, so it will change with time. If you are sprayed water-based finish, you need to disassemble the gun more because the pin will rust. You can't just blow it out. Your spraying goal is to mist the surface. That's especially important if your surface is vertical. Drips are not desired. On horizontal surfaces, you don't want puddles. Before spraying anything, I connect the gun to air pressure and spray it empty in case there is any leftover solvent in it. Then I disconnect it. I support the gun between 2 gallon paint cans. I pour in the amount of the product, thinned appropriately as needed. I had previously drawn a line through the diameter of the material volume screw with a Sharpie. If I needed to disassemble the gun, I wind in the screw all the way, then back out one full revolution. With the gun tip being held over the can, I pull the trigger and wait and watch for the material to drip out. About 1 drop/ second is about right. Next, I lie the lid on the can. I attach the dessicant filter to the gun. Next, I attach the air hose to that. I wipe off the tip of the gun. I fire once in the air. Unless I'm outside, I always wear a respirator. The air volume screw near the bottom of the gun should be in the middle of its range. I begin spraying, adjusting the spray pattern and material volume screw as needed. After spraying, I return any unused material to its can. If it is polyurethane or an oil-based paint, I spray in argon (Bloxygen) per instructions, and rapidly reseal the can. Water-based products and lacquer don't need argon because the dry by evaporation or catalysts and not by oxygen-linking. In general, I use more solvents in gun cleaning than finish material. Paint thinner doesn't work very well, but it's cheap (relatively). The used solvent goes into a waste bucket except for water and DNA, which can go down the drain. Since the cost of water is near zero, I use a lot of it when cleaning the gun (after spraying water-based materials only). Standing over my utility sink while the solvents flow out can be tiresome, so when using water, I place a rubber band across the gun trigger and let the water drain out while the gun is standing up in the corner of the sink. I continue to wear the respirator when cleaning with lacquer thinner or MS. After the gun is cleaned, I recheck my work piece for any drips. Depending on the material, I'll use a clean edge of Bounty or a fine paint brush to spread out any drips. Drying times and curing times are different. Polyurethane is the very best finish, but it takes 21 days to cure. Lacquer dries the fastest, but it is very toxic, it requires a near-perfect spraying temperature and it crazes, which makes it a terrible choice for table tops. Brushed on Deft never seems to cure. Shellac is relatively non-toxic, but it and the acrylics are permanently damaged by alcohol products. There is no ideal choice for finishing materials. No matter what I build, it is the final finishing results that determine its quality.
What is the tip size you are using lacquer/varnish? I have that same gun but I either get a dull application or when I go slow and look for a shinny application it is heavy and most of the time runs. I haven't tried this air setting approach, I will try that this weekend. I just set it in the green zone I think that is 60/65 lbs.
unfortunately, the video stops at the point where the pressure is just right, but no indication on how to adjust the material feed.