Does anybody have methods to safely paint metal in cold weather?
I want to address my E46's subframe this winter. It'll be done in an uninsulated garage so I expect the temps to be low-40's. Last time I did this to my E36 in high-40's temps, I draped plastic sheeting around the car and had two space heaters cranking. I popped my breaker a few times doing this and am wondering if there are any better options.
Are there any safe homebrew methods to keep metal warm and allow paint to cure properly?
Read the datasheets for the paint you're using. If you're a few degrees (but not too much) below the minimum specified temperature and it's not a water based paint, the paint will typically still dry. Just allow for significantly longer drying / curing time than you would even at the minimum specified temperature. A bit of heat will help, of course. If the paint is spec-ed for use down to 50*, you don't need to try to keep the metal at 70.
Spray bombs? Dunk the can(s) in super hot water in a sink about 10 minutes before you begin.
Spray a lighter coat than you would otherwise.
This is the sum total of my spray knowledge
Pre heating the can and an infrared space heater pointed directly at your work plus light coats go a long way. Not sure how this holds up to something like a subframe that's more exposed to the elements, but it's also worked for me for painting RC bodies in winter (as well as underhood and house stuff).
Sounds good guys. Yes, I'll be using spray cans. I'll keep in mind the lighter coats and try to find the warmest week possible. I'll be a solid 15 degrees under the temps recommended, so it's gonna be a challenge.
I painted some wheels 24h ago and they are still tacky.
HEAVY orange peel where I did not realize that while it was 45 outside it was closer to 30 in the garage.
As it turns out, that knowledge I presented earlier was less than a day old 
The faces turned out better.
I believe there is a law against mounting rally tires on wheels that are not white.
I assume that keeping the cans indoors is going to happen. Warm paint on a warm surface should go a long way.
I follow much the same routine - try to preheat the part - I have a space heater and hang the part right in front of it. Pre-warm the paint cans in a bucket of HOT water. Quick coats then let it cure out in front of the space heater.....
My garage can be as cold as 40* (when it's in the teens-low 20's outside) and on those days I don't try unless I simply have no choice. We usually get a day or two in the 50's-60's if I can wait a bit, then I need everything prepped and ready to go for the warm day.
If it's 50+ and sunny, I hang the part up in the sunshine to try and at least get it cured out enough not to run
Can't hang the underside of the car anywhere! I'll be welding in subframe reinforcement plates on the chassis, not working on the subframe that is coming off. The chassis is going to be a huge heatsink, but I'll remember to preheat the area with a heat gun before I spray away.
If you've got a set of those big halogen work lamps, use them. Pointed at the area for a bit before painting, while painting, and for a bit after. They'll put a surprising amount of heat into an object a few feet in front of them.
I painted a number of body panels in an uninsulated garage during Michigan winters with good results. I kept and mixed the paint indoors so it was at room temperature when sprayed. I aimed a small heater at the panel I was painting and let it run enough to heat the metal to the data sheet temp recommendation. Right when I was ready to spray I would shut off the heater, wipe down the panel, and then spray. As soon as the overspray settled I would start the heater back up (but further away from the panel) and let it sit until the paint was somewhat cured.
For wheels, fenders, bumpers, etc. once the paint wasn't tacky to the touch I'd try to move the part into my basement to dry for a day or two.
HEAT is the answer.
My methods include using a torch or a torpedo heater to heat up the part. Get it HOT. You'll be amazed how fast and nice it comes out as you shoot paint on it. I do this pretty regularly. Rattle cans is what I spray with and as long as the paint can is above 50ish degrees is doesn't seem to care much.
