I have an old frame and it has 2 layers of paint and a primer I need to take off. What is the best way. I've tried sanding with 40 grit sand paper but it just wares out too fast. Will paint strippers work?

I think using paint stripper would be the easiest by far.

It is likely that your coating is actually a powder coat that was baked rather than paint that dries. In any case removal is the same and it won't use 40 grit paper. Paint remover or gel is good and so is sand blasting if you have the equipment.

You can use paint stripper, and some people do. I don't personally don't like it. I wouldn't hand sand it either. What I would do is strip the frame down and then sandblast it. You don't need to sand it down to bear steel, but it won't hurt if you do. You need a sandblaster and an air compressor of some kind, you can use play sand in it if you have it, I have used play sand before and ran it threw a strainer before I ran it threw the sand blaster to take out and rocks. You can also use a palm sander if you have one but it would be easier to sandblast. Just where glasses. Then you can reprime and paint.

40grit is a little heavy. If I was using a palm sander I would use 80 grit and that would take it down to steel in seconds. 180 grit would work too.

Have it blasted. If it is powder coated you will spend way too much money for stripper and be breathing all the vapors.

If you believe it to be powder coated, try lacquer thinner.