Equipment needed for Frame-building?
The minimum tool set is something that gets discussed on the framebuilders list and other forums from time to time. I think the consensus is:


a heat source, usually oxy-acetelene or arc welder but you can start with MAPP (oxy-propane) which is cheaper.
a cheap hacksaw and 32tpi blade (technically you could use a file instead but don't)
a half-round file
a drill (even a hand drill) and 3-4 drill bits
a pen or scribing tool (even a nail will do)


Ideally you'd have more than that but you could build a bike with only those tools. But that is "making a point" territory. More realistically you would add:


a vise, preferably bolted to a workbench
a decent hacksaw and several blades
several half round files and a flat file
a set of locking pliers (vice grips or similar) to hold hot metal with
a hand punch (spring punch)
a small paint brush for applying flux, and a wire brush for removing it (if you're brazing)
a grinder with cutting and grinding disks and a wire brush (easier than hand tools for rough work)
an internet search engine, for answering random questions at odd hours :)


If you want to start building bikes I strongly suggest joining the framebuilders list or some of the online forums. There's a heap of things you can do to make your life easier, and having someone you can visit to see how they do stuff will teach you things you don't even think to ask. The Atomic Zombie crew or other garage homebuilders would be perfect if there's a group like that near you. Recumbent homebuilders are often equally useful and will probably help you even if you want to build a wedgie.

The advantage is that you built it yourself, and if you want something unusual you can build it. The disadvantage is that it's an expensive, time-consuming way to get an inferior bike. The first one you build will not be professional quality, you'll be lucky if it works at all. So if you want a traditional diamond frame bike the only reason to build it is because you can (like Suzy did). If you want a weird bike then you might find you have to either pay a professional framebuilder or do it yourself. Unless you already have a metalworking shop, it's cheaper to pay someone, even if they've never done anything like your bike before (so you get a first attempt that kinda works).

The reward is that you get something you built yourself. It's especially fulfilling when someone you approached initially who refused to build it sees your version and turns it into a commercial product (Greenspeed make a tandem that converts to a solo trike now, because I showed them it could be done).

(moved from Items required to manufacture a DIY bike?)