I'm still vey much at the beginning of my spray finishing learning curve, pretty well confounded by having too many variables that interact with each other in complex ways. Changing one variable at a time does not seem to be a productive approach, as the variables are not independent. I don't know how to quantify the results well enough to take a fractional factorial design of experiments statistical approach. So asking the experts seems like a reasonable alternative.
At first blush it seems straightforward; the controllable variables are, I think:
1) viscosity of finish
2) pressure of finish delivery
3) volume of finish delivery
4) air pressure
5) air volume
6) tip size
7) speed of movement of the gun over the surface
8) distance of the gun from the surface
9) fan width
I'm spraying with a Qualspray AM-6008 HVLP gun. The finishes in question are from the Target line, EM1000, 2000, 6000, 8000.
My most consistent problem is a dappled appearance, as seen in the picture below. This is taken wet, it flattens out a lot as it dries, but not completely. I bought a thickness gauge to try to see where I was with coating thickness, it worked OK with pigmented finish, I can't figure out how to read it with a clear finish. I can't tell the difference between the probes that are wet and those that aren't. I'm starting with the gun settings per Jeff Jewitt's recommendations.
I thought that increasing air pressure and/or decreasing finish flow should help, I've managed to create a whole lot more overspray, but it still seems to spit droplets in with the mist, giving this dappled look. I've sprayed gallons of water onto the side of my shed playing with the various parameters; I've not yet found the combination that produces a uniform mist. It's gotten better, but I'm not convinced that this is the best it can be.
What's the most productive thing for me to try?
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