How do I attach 2 pieces of metal together without a welder and still be structurally sound?

get 2 screws and matching nuts , drill 2 holes and pu the nuts on then 4 extra support maybe duct tape orwell idk thats my answer :)

one simple word, duck tape

By the time you buy enough epoxy, rivets, and bolts, you could've already bought a cheap stick welder and some rods.

Brazing or soldering... It's like welding but much cheaper. Or just buy a welder... once you start... you will never stop.

tube and sleeve, if the part you are trying to join is hollow you could put a tube or bar stock into it and secure it with a drilled hole and bolt, or even jb weld. the tube or bar stock would be the structural component.

This is an application that I would consider purchasing the right tools for. When you ride any vehicle, you're gambling your life and well-being on it's structural integrity. You need strong joints that can take abuse. The strongest solution is a good weld. A basic welding class and tools can be found for under $500 in most of North America, and it's usually well-worth the investment. I am not trained, but I own a little arc welder ($100) and I can do some basic joins... this has earned me many dozens of refreshing beverages by using my modest skills to help my friends and family. Ordinary nuts, washers, and bolts are the second strongest solution, however there are many engineering intricies that determine selection and use of these. I recommend this solution for a prototype, but with the caution that you should build it 10x stronger than it needs to be and you should monitor carefully the condition of your fasteners. The third strongest solution would be a JB Weld or Quiksteel, however neither are designed to take repeated impact. I do not recommend this. PLEASE DO NOT USE GORRILLA GLUE FOR THIS. Gorilla glue is very strong, but it's not that stong. I've been able to break Gorilla glue joints with my hands.

Bolts or rivets. Get an engineering manual (Machinery's Guide, for example) in order to do the calculations you will need to be safe.

Try some QUIKSTEEL Epoxy. It's like a putty, you cut off what you need, and you kneed it with your hands. it doesn't take long for it to set, but holds just as good as a weld does. You can even use it underwater. It's pretty good stuff. You can most likely find it at a hardware store, or possibly even wal-mart.

. A lot of epoxies will be too brittle for use on a bike. Most glues will not be strong enough (although I have zero experience with Gorilla Glue). . Binary Boy's bolts (or screws) and clamps should work well for proof-of-concept but probably won't hold up to hard use. . klee27x's brazing idea should work best but if you don't have access to a welder, you probably can't get your hands on a good torch.

bolts and clamps

try the JB weld. works for me ussually.

Google "brazing, silver soldering, silver brazing."