Tip size varies, depending on the gun type, input pressure, primer type, and reducer temperature. Use the larger tips and experiment on a scrap piece of cardboard; vary the thinning ratio, input air pressure, and spray volume, holding the gun about 6" to 10" from the surface, until you get a nice, smooth application without runs. Bigger tips are good with primer, so you can spray it "thicker", but watch out for orange peel and runs (just wastes primer).
For K-36, start start out by thinning 100% to 150% and about 40-45 psi (siphon or pressure feed type gun) or 30-35 PSI (HVLP). Experiment with thinning and air pressure/paint volume adjustments from there.
It's not that complicated, you'll find a combo of settings that works for your equipment. Note them and re-use next time. Don't be afraid to practice and experiment with your gun's adjustments.
I used to use relatively inexpensive pressure and siphon type touch-up guns for spraying primer and occasionally still do - they work great for hobby projects. Harbor Freight makes a $25 touch-up gun that works great for primer (but stay away from the $65 small HVLP unit, the purple one - it sucks).
These days I pretty much exclusively use "pro" grade SATA and Devilbiss HVLP guns and the tip size will vary with what type of primer and reducer temp I am using. Typical tip size for the SATA Minijet that I dedicate for primer use is .15 mm.. This is an awesome gun for hobby and touch-up use, but pricey (around $165). I used to use the same gun for everything from primer to clear by changing the tips and spray patterns. Now I have three guns, for primer, color, and clear - no need to change anything, just switch guns (I paint 10-15 R/C models - now rockets - per year, it's well worth it to me).
BTW, it was a pain learning to paint and finish well, and buying good equipment, but the attached picture shows what you can do once you become proficient....that's a $5K paint job done in my garage for about $450 in materials and 60 or so hours of labor.
Barry
