I have too many thoughts on this topic.
#1 though is: it is dangerous to make/modify stuff and ride it - (also SOOPER FUN!) but also you could get hurt
so a bunch of things to keep in mind in no particular order (MIG):
if someting suddenly feels "springy" i assume i just broke a weld and i stop
welding is not hot glue- it needs to penetrate both peices of metal
practice A LOT- thicker material is easier to get the hang on, surfaces are easier than tube ends, ends to surfaces are tricky - definitely smart to start on things that don't support a human (yard art, f'rinstance)
HOW you put it together matters. i try to have peices stacked on top of one another, or pushing against one another, or inserted into one another- rather than relying strictly on the weld.
butt joints subjected to shear forces (sideways) are prone to failure
over heated metal may be prone to bending and failing (breaking) after it is cool
making long things that act like a lever (chopper forks) puts A LOT of force where you may not expect it. these forces tend to find crappy welds, and bust 'em (particularly when going over a bump at high speed).
slugging up butt joints makes 'em way way sturdier, and if they do fail, the joint usually stays together. i use full lenngth slugs on my builds. this also makes the frame stiffer, so the "pass it on" game of force to aweak spot continues.
good fit before welding makes better joints
excessive grinding of weld may weaken a joint. i leave mine and compare my work to itself over time
do grind off any coating on the metal in advance- paint really messes up the weld, so does galv, chrome, rust etc. (plus health)
weld some scarps together then clamp one side in a vise and try to beat the weld apart. try this a few times, see what happens.
bikes are tough to learn on since the material is thin, and round tube makes it suckier as well, since constant distance keeps the voltage regular, and the sheilding gas in place.
there is a reason bikes have evloved to look the way they do. creating an object that can take the pounding forces (+ ergonomics) is why bikes are the shape they are. change it at your peril.
i use a MIG because that is what is available (along with plethora other tools) where i usually build. i actually prefer my flux core machine (fcaw), because i can cause the voltage to drop by running the welding wire out (say 1' - 1 1/2" long) matching the heat to the material thickness (thinness?) with constant sheilding gas. fcaw also does better on rust and crust and paint (remeber health tho). long wire on the MIG causes the sheilding gas to disappate= nasty weld - can be challenging to dial it in
welding my chopper mopeds is one of the most satisfiying things i do.
keep in mind there is risk involved with welding your own setup.
practice
think
whew! at least as long as i feared
el
