Originally Posted by Gbrebes
I agree with everyone else that TIG welding is the best choice, but the equipment can be expensive. I would also like to offer acetylene/oxygen torch and brazing as a valid means of fabrication. It can be a more economical way to go.
I modified my bike frame using brazing and it has worked out well. Every joint I welded had an internal sleeve inside the main tubing to strengthen the joint. I did end up developing a crack in the front loop near the bottom bracket. I rebuilt this area with two gussets attached to the bottom bracket and welded to either side of the tube.
I also agree that the frame is the most important component, strength wise, and that extra attention must be given to stress points, like head tube, rear chain stays, dropouts, and bottom bracket.
I have to agree with Gilbert here, I have been teaching myself to weld for the past two years, staring on small projects, and working into more complex ones.
I started with a cheap MIG and a cheap TIG, and I learned after many poor welds that I should start with the basics if I am teaching myself
I started oxy-acetylene welding, and have been making progress in my welding proficiency much faster.
If using steel, brazing, using lugs, is preferable to TIG for the same reason TIG is preferable vs other types: much lower heat needed to bond the joint. This means even less thermal distortion, and a stronger joint.
If it has to be aluminum, TIG is the best way to WELD it, hands down. But that doesn't mean you can't use the lug technique and glue the aluminum into the lugs, many OEM bicycles are constructed like this, with a bond many times stronger than its welded counterpart.
There are also many resources -http://www.paragonmachineworks.com/mobile/
comes to mind- that you can go to for pre-made frame sections, and the various lugs to join them together.
I also agree wholeheartedly with the members advising caution in building you own frame.
This does not mean you are not capable of building a mechanically sound motorized bicycle frame. Just make sure you do all the research, and TRULY understand the forces that the bicycle frame has to withstand under the strain of driving at speed.
I wish you the best of luck!