Quote from another thread:

Yes.

Here are a few basic tips I learned when I apprenticed for a painting contractor. They apply to painting any complicated object.

(1) Say you have an area in front of you that has crevices and angles, as well as flat surfaces (for example, a passenger car vestibule). The first thing you should paint are the crevices and inside corners. Make passes at those with your gun until they are coated. Only after those crevice/crack/corner places are done should you apply paint to the flat "field" surfaces of the object. In most cases, these field surfaces will already have paint on them due to incidental over-spray from your work on the corners and crevices. So then all it takes is a few quick passes over these flat places with the gun to take care of them. Just remember, the flat areas mostly take care of themselves if you just be sure to paint the corners and crevices first.

A common mistake among non-pro painters is to paint all the flat field areas first, then afterwards try to direct paint into the corners and crevices. The end result is too much paint piles up on the object. It builds up so much that it starts to run, which both looks awful and is a waste of material.

But the even bigger sin is just painting the flat field surfaces and ignoring the crevices. It happens all the time among amateur painters! Of course, the corners are where the joints are that hold your object together. Without paint on them, the joints rust, streak, and eventually fail. The sad thing is that a huge amount of restoration, metal work and prep work can be lost due to a poor paint job like this.

(2) Another tech tip is to release the trigger after each pass. The non-professional always keeps the trigger held down at all times, which results in a build-up of paint wherever the painter changes direction of the gun. I watched a RR museum volunteer doing that on a Youtube video (cringe).

(3) Move your painting arm like a robot. Keep a uniform speed and uniform height above the object. When you get good, you can also feather the end of your pass with a quick turn of the wrist up and away from the object. Combined with step #2 above, you will look like a robotic painting machine when you are at work. And after years of practice your paint jobs will start to look perfect.

These are a few I could think of. Like any craft, the best way to learn is to apprentice with a professional, though I realize that is not always possible for the average volunteer.

And stay parallel to the object. One of our guys painted like he was leading a symphony orchestra. And what he was painting looked like it. Also spray past the ends like mentioned above.

look for a local VOTEC that offers evening classes in auto body painting, You can learn prep, mixing paint including the new water based paints. Plenty of practice time in a paint booth.

Also, plan ahead how you are going to paint the object. On large objects where some time might pass before you get back to your starting point, look for an outside edge to start and stop at, that way, when you are back at your starting point, there is an natural "break in the finish surface so your over-spray doesn't strike the already-setting start point paint. On a locomotive, a cab corner is good for this.
Paint application is a science and an art. Some paints require a thin "start coat, followed by a normal "wet coat, and most need a double-wet coat application to have enough mils (thickness measurement) in the final finish so it will last many years.

As someone who has done painting on both railroad and non-railroad industrial equipment, my advice:

SUIT UP. Get those disposable body suits and USE THEM. Respirator and all. Even when it's like wearing a sauna.

The two issues are cosmetic and inhalation hazard.

The same stuff that makes catalyst paint last is the stuff that makes it all but impossible to come off of skin, hair, fingernails, etc. Nothing short of practically a bath and scrubbing in acetone (itself nasty stuff) will get the stuff off.

I don't need to lecture you about inhalation hazards. The problem is, once you get good at it, they want you to do more of it (see also: cooking, cleaning, electrical work, etc.). Someone painting one antique car might get away with a bad day breathing the stuff, but not if you do it repeatedly.

A related aside: no fewer than three of my rail associates have come down with bladder cancers. The tie: All three were model railroaders that did extensive airbrush painting of models.

Amen!! The tyvek suits are very cheap, cover up, this stuff is absorbed through the skin--and especially through the eyes. Get used to being in your own private sauna. When I was painting locos in Portola, I was known as "Orange Man" as the suit would become rather orange, even with the HVLP unit I used.
I too, have heard of modelers dying of complications from exposure to the modeling paints. Paint is dangerous, respect it!!

The problem is, once you have proven to be able to 1) paint well and 2) be willing to go through the rigmarole, you get LOTS of requests to paint, and one project becomes ten.......

One thing that I am surprised has not been mentioned is the surface prep. You can be the best painter in the world, but if the prep work is bad, then either the job will look bad or will not last and all the money spent on paint will have been a waste. I see this so often it makes me sick. You are always better off to spend the time and money on the base, and if you have to go cheap go cheap on the top coat. A good quality base and prep work with cheap paint can look good and last years.

Very good point; probably because those of us who have "been there, done that" assumed that part of the process. Ah yes, one should never assume. . .
Very true, preparation is critical, elimination or stabilization of corrosion; where access doors exist, pre-finishing of the openings; cleaning (with de-greaser) of the surfaces (some modern finishes are VERY susceptible to failure from contaminants that older systems weren't troubled by); and proper masking. Masking often takes more time than applying the finish!
Speaking of masking, one should consider (on multi-color schemes) which colors to apply first, for instance, reds tend to bleed through when overcoated with other colors, silvers can have problems hiding the undercoat AND cause poor adhesion to overcoats (double-whammy). If you can paint the lettering color first, then mask it (self-adhesive lettering masking is a great invention!) and apply the other colors, the lettering will last longer as it's just a little lower than the surrounding finish--although this does require careful de-glossing around the stencils to get good adhesion of the paint layers. Once again, preparation, preparation, preparation! (In Real Estate it's Location, Location, Location) :)
And yes, there is the danger that if you're good at it, you'll be asked to do more!

Of course, the other thing is you don't have to spray. You can get very good results using brush and roller painting with less environmental concerns, and for some old equipment a sprayed finish is simply not historically appropriate at all. I did one job in an area where we were under a microscope and in a very visible location, and found a PPG water based industrial paint product that was applied by brush and roller and worked out very well, and has passed the test of time for about 20 years now.

Number 2 tech tip. I used to do a fair amount spray painting and was taught that you release the trigger to stop the paint flow but keep the air going through the gun. This keeps splatters and heavy build up from happening when you once again release the paint into the gun.

Masking can be done in several different ways. What I have found interesting is observing how the layers of paint were applied to cars or locomotives -- study this before sanding the old paint. Then you may have to sand off the most recent paint job(s) to find the color scheme you want to recreate. They maybe continue on down to the metal for the prep.

I have seen some passenger car paint jobs that were painted the smallest (narrowest) stripping to be painted first, then that gets masked and the next color is applied, it gets masked off and the next color is applied, etc. until the largest color area is applied. With some paint jobs the black edging of letters and of striping was applied later by hand.

Then there is the photo series of the Union Pacific sleeping being painted by Pullman (this was published in Trains Magazine a long, long time ago). The yellow body color was painted first. Then the red strips were edged with mask, the red lettering was cut out of strips of mask, and the rest of the car was encased in brown paper, covering all of the car leaving only where the red was going to be applied. That red was sprayed on and after drying all of the brown paper and the mask was removed to reveal the completed paint job.

This is very likely because they found that they couldn't cover the red with the yellow without burying the car in paint. Yellow is a notoriously transparent color, second only to red for its lack of hiding power.

I'm going to take exception to the advice above to paint lettering color over the general area of the lettering, mask, then paint the final color. Yes, it was often done this way in the past, but... This isn't your grandfather's paint... with the banning of heavy metal based pigments, colors don't cover like they used to, and contrasting backgrounds may still show through a surprising number of top coats. I'm of the opinion that the body prep should end with a solid coat of primer over the entire car to blend all the patches together, then paint the largest body color, masking to keep overspray off the area to be occupied by other colors, and finish up shooting the lettering through stencils. If the lettering color is known to have problems covering the base color (test first) a coat of gray primer can be shot through the stencils first to help "brighten" the color.

Yes, Reds tend to bleed through any colors painted on top of them. Lettering is usually a light color, so seldom effects the body color--however, if you are worried about the, you could shoot some matching primer after masking, If the lettering is the last thing put on, it will be the first thing worn off.
OTOH, seldom does this equipment get mistreated like it did when in general use!

Solvent vs Water Based paints
I hope would be spray painters understand that solvent based paints are on a major phase out depending on the area you reside. it will be nationwide by 2017.
Pennsylvania, Delaware and Maryland have a cut over date of 2016 for all body shops with the typical spray booth equipment. After that you must have a full capture of all exhaust into a containment system. If your state goes water based most solvent based paints will phase out.
DO NOT get caught in PA spraying solvent based paints outside without a control system in place.
Bad news you will need new spray guns and measuring equipment (which you should have anyway) and air based fans for the new paint. Good news it is a two stage based system that anybody with a good trigger finger can spray. The whole game changes in 2016 so check with your local paint supplier for local code information.
I am learning water based paints in January (VOTEC) via PPG instructors. I have worked with a local body painter to get ahead of the curve, it is a very different process.