James, Daniel and Don thanks folks. vinyl tracks are bane of armor modelling i'll say no more, anyone who has the means should invest in proper aftermarket especially if the tracks are exposed and have slack in real life so they can be made to sag.
@Dan thank you. the answer would be a loaded one so bear with me but tl,dr: trial and error = experience.
i am using a sparmax with a 0.2 needle.
i do unscrew the crown so that i can get in as close as possible resulting in less overspray and finer lines. by close i mean airbrush almost touching the model close. overspray is a combination of several parameters i'll get to later.
my pressure during a freehand camo/line is probably less than 15psi but don't use mine as a guideline because some airbrush will need higher amount of air passing tru in order to atomize the paint properly. nozzle size / needle diameter isn't the only factor in achieving a fine line, what psi setting at your given room climate and paint consistency your airbrush needs, only you can figure out. besides listen to the airbrush, colors are colors because of their consistency (thin = light, thick = dark) and a properly thinned white paint will sound different than a properly thinned black paint coming outta nozzle at a given psi keep that in mind.
wrt paints, i do not thin paint but instead i tint the thinner with paint. tamiya acrylics along with their lacquer thinner can do this whilst still be able to cover to an acceptable degree. other paint brands and types may not, again you have to figure out the consistency with your own setup and paints you have access to. tho understand this method may require your painting habits to change especially if you are going in gungho with airbrush blazing like a spray can on a car model. since the paint is barely there you'll have to be patient and work little by little, panel by panel and build the paint up.
now the problem with tamiya acrylics thinned like this is they'll lose "body" (for lack of a better word) and can have a problem grabbing the surface - not talking about color coverage here! in order to remedy this *if* you need to lighten up the color use their gloss colors like gloss white or gloss yellow. if that is not possible use their clear gloss instead. you may see that this also helps with the overspray especially if your airbrush nozzle / needle is not particularly healthy!
for ex the green lines on the elefant were mixed 3x nato green + 2x field gray + 1x buff + equal amounts of gloss clear to the total + touch of clear green
the dark yellow was 1x dark yellow + 1x gloss white.
ergonomics is another factor, i make sure the model is secured at a proper angle to the airbrush because i am using both my hands to hold the airbrush; right hand is only for trigger, left hand is for support and actually guiding the airbrush! the lines on the elefant i drew with a water color pencil onto the model first so that i don't need to pause and check the crappy black and white instructions of italeri. this will help in fine lines especially since the speed which you move airbrush around has a direct impact on the width of the lines - faster the movement finer the lines less chance of paint running on the model but harder to control, this is where the lines drawn onto the model come in especially handy.
as you can see the amount of factors that has to converge all at the same time and at the same spot make a long list but writing/reading is actually harder than doing; go in and experiment - nothing beats the hands on experience. even if you can't achieve the finesse you are after at least you'll figure out the limits of your equipment - by definition all machines are female since they multiply utility but the responsibility of knowing the capacity is on the user, asking something the tool is incapable of would only result in headache at best.
22. September at 06:56:52