I have been painting motorcycles, cars, and bikes for something like 35+ years now.
I started off like most, with rattlecans in the garage or driveway, but I got bitten bad by the kustom kraze in the early seventies, and wanted to airbrush, and pinstripe, just like ed 'big daddy' roth, so I went out and got brushes, a paasche VL (good ol airbrush) and just completely screwed up perfectly good looking motorcycles, cars and bikes for a year or so (all my own, thank god), but eventually I learned the rattlecan way, the hard way, the easy way, the fast way, the super uber quality way, and just about everyway in between.
since most of you can probably (or already have) figured out the hard way, the rattlecan way (which looks good=not for long though), the easy way, and the fast way, I'll detail the "reasonably fast, but still high quality way" which is, by the way, a PERFECT way to paint a something metal if you hate sanding; I have never met anyone who loved to sand things down, so I'll assume most of you will be with me on this.
this assumes you have access to a compressor, a HVLP or LVLP paint gun, a respirator (dual charcoal dust/mist type), a detail gun is also helpful (tiny paint gun w/ a 3" fan pattern) and a space to paint free of any ignition sources, and with good ventilation: usually painting outside with the ground wetted down, and then the piece moved into a sealed up garage after painting works VERY well) be VERY careful about overspray settling onto neighbors property as nothing will [censored] a neighbor more than finding the car dusted with paint overspray. (so you get tarps, and offer to cover the nearby cars)
here's what I do with just about every bicycle frame I paint now:
A) TEAR IT DOWN COMPLETELY: headset cups, BB and all, nothing looks more amateur than tell tale overspray on chrome or shiny bits, because they should have been removed, not masked off. if you are going to remove any braze ons, eyelets or cable stays do it now now before the next step.
This also includes brazing new ones on, if you want, the point is to get all the metal work done before the going to the blaster.
B) TAKE IT TO A BLASTER: and have them blast it: note! tell the blaster if the frame will be powdercoated or painted, because they will want to use different blasting media, for each type of coating.
this is usually something like $20-$40
I HATE chemical strippers for ONE REASON: you cannot get all the stripper off: it's impossible there will be tiny specks left in crevices, and once painted these specks will start to remove YOUR PAINT JOB! so take my advice after 50 or so bike frames, and too many motorcycle frames to count, GO TO THE BLASTER, it's easy, it's fast, you get bare metal, and no residue (just remember to blow all the leftover media out of all the tubes!)
C) CLEAN THE DANG THING! paint will not stick to oil or grease, hamburger drippings, or taco juice and that includes the oils from your hands. (taco or not)
steel can be cleaned with alcohol or mineral spirits.
for aluminum I reccommend PPG's aluminum cleaner (quart=$10@ body shop supply houses or "color shops"😉 once cleaned DO NOT TOUCH IT WITH BARE HANDS, USE GLOVES. (NOTE: if powdercoating, now you would put it in a plastic bag, and deliver it to the powdercoater)
D) SEAL IT/FILL IT/SEAL IT AGAIN: using a decent 2 part EPOXY BASED NON SANDING SEALER. (PPG, House of Kolor, DuPont etc,...)
this is special stuff, and is just a god send if you remember acid etch primers.
this sealer is designed to go over just about any type of bare metal, sealing it off from oxygen (no oxygen=no oxidation: rust) and provides a topcoatable surface that can be directly painted over with NO SANDING NEEDED, for something like 5 days. follow the "p" sheets (instructions) available online or where you buy the paint and shoot two good coats, waiting about 15 minutes between each coat (USE A TIMER! DON'T GUESS)
in the old days, you had to scuff the etch primer after it cured or your stuff would peel off in sheets,...not anymore.
now you'll need to grind all the braze on sites so they are a tiny bit LOWER than the surrounding tube, use a file, or a angle grinder, but obviously be careful, and don't go very deep at all, you just can't have anything sticking up from the repair area. to fill the tiny grinder marks or little indentations where you removed the braze ons, you use a GOOD QUALITY filler (NEVER, EVER, EVER, EVER USE "BONDO" brand from kragen/shucks whatever, EVER!) I use "METAL2METAL" from evercoat, it has powdered aluminum in it, so it's like filling with lead, except no stunted growth or brain and nerve damage from lead fumes! (no I never used lead, nice try!) sand the filled areas down with 180 grit sand paper on a HARD block of some sort: if the block is longer than the area you are sanding, and you sand along the length of it, the area will be nice and flat when done. you should sand in a "X" pattern for round tubes, so the filler profile after shaping/sanding matches the tube profile, and you get an undetectable repair. NOTE!! only sand down the areas you are repairing. now blow on another two coats of the sealer, and after 30 minutes look at the frame, it should be all smooth, and even, with no tell tale sanding or grinder marks visible anywhere,...if you see some sanding scratches, wait another hour, and then another coat of sealer, and check it again. REMEMBER: paint will NOT hide anything (except white paint), in fact it will highlight ANY surface imperfection ESPECIALLY if you are going to use a metallic or pearlescent color coat.
E) BASECOAT: I prefer modern urethane basecoats which will chemically bond with both the substrate (the epoxy sealer) and the clear topcoat, creating a nearly solid paint layer from bare metal to surface: VERY tough and durable, and polishable YEARS after painting. the only real tips I can give you for this are: 1) use the proper temp range reducer for the painting area (thinner for urethanes) this is CRITICAL if you are applying a metallic or pearl basecoat or the tiny flakes wont settle properly and the surface looks grainy and bumpy, this is called "MOTTLING", less critical for solid colors.
(TIP: Less is actually,...LESS: only shoot enough LIGHT coats of the base to get "HIDING" (you can no longer see whats underneath) once you get hiding STOP SHOOTING. the basecoat dries in minutes so a common mistake is to just start hosing the thing down with multiple coats, DO NOT DO THIS! shoot for hiding, and even color and then stop.
F) CLEARCOATING: (USE A FREAKIN RESPIRATOR, DUH!) this is the most technical step; everything usually goes GREAT until you get to the clearcoat and it falls apart fast, so tips learned the hard way: USE A PRACTICE PANEL FIRST!!
the BIGGEST (and most common) rookie mistake is to try and "learn" how to shoot clearcoat ON the thing you are trying to paint, again DO NOT DO THIS unless you have experience shooting urethane/polyurethane clearcoats ON TUBULAR SURFACES, and thats the rub, just because you know how to lay glass on a car hood, or motorcycle tank, don't think you can just start shooting tubes and not have a learning curve.
so "ALL PAINTERS MAKE MISTAKES, BUT THE PROS MAKE THEM ON TEST/PRACTICE PANELS NOT THE PROJECT PIECE"
I would get a section of steel pipe and set it next to the frame and when you use the epoxy sealer/primer shoot the pipe at the same time, and shoot the base on the pipe as well when you basecoat, NOW you have a perfect practice panel, and if you screw it up (orange peel, or runs, it'll happen) you can just wipe it all off with thinner and start again: the epoxy can be topcoated 20 minutes after shooting, same with the basecoat. once you feel proficient THEN you shoot your beloved PX-10, grand jubilee, colnago whatever.
G)SHOOT A COAT OF CLEAR: thats ONE even pass over each surface: for tubes I shoot lengthwise once on top, once for each side, and the bottom, so four passes (with about a 50% overlap) then move to the adjacent tube. for bicycles I like FOUR COATS, BUT!!! YOU MUST WAIT AT LEAST 15 MINUTES before shooting the next coat: here's a great trick for determining when the previous coat is ready for the next: on the masking (headset, bottom bracket or anything nearby, thats NOT the bike) touch your gloved finger to the clear after shooting and pull it away: directly after shooting it will pull away clean, after 2 minutes you see "strings" when you pull away, and after about 15-20 minutes it will just be tacky, and will no longer "string", now it's ready for the next coat. (this is assuming a 70 degree painting area, colder will take longer, hotter will be faster, don't paint under 60 degrees or over 85 degrees for best results)
now keep in mind that the clearcoat has a hardener, and that hardener starts doing it's thing the moment you mix them both together, how long you can work with it is called the "pot life", so only mix enough for for two coats, and then mix another batch for coats 3 and 4, or your 3rd and 4th coats will go on gloppy and you'll get orange peel of biblical proportions.
you don't paint your bicycle frame to save money, if your trying to save money, have it powdercoated, you paint your frame because it's a very satisfying feeling to ride something you painted, when you stop, and people ask "who painted that"?, you get to say "I did" and then bask in the compliments, or simply ride feeling like you took part in more than just the selection of components and assembly of your steed.
my current bicycle wont be painted till spring, so here's a 62' dominator (almost as cool as a fixie)
peace, love and isocyanates