I have an old ten speed that I am converting into a single speed, since the derailers are no good and I am not very comfortable with down tube shifting anyhow. I am in the process of removing all the old paint and planning on repainting it. Before I do that I would like to weld some nuts onto the frame for a water bottle cage and for a rear rack. I will not be doing the welding myself, but my buddy at school will be doing it. In our shop at school we have access to mig, tig, arc, and acetylene. I am unsure if the frame is composed of cro-moly or steel. So my question is, which welding method is best and what settings should we use?
Cro-moly is steel; it's just a specific steel alloy containing chromium and molybdenum.
The water bottle cage bosses and eyelets for the rack are called "braze-ons", and should be, uh, brazed on (not welded). An oxy-acetylene rig would be the best for this application, and for filler material you could use either brass or silver with lots of the appropriate flux.
The brazing procedure will be the same regardless of whether the frame is hi-ten carbon steel, cro-moly, manganese-molybdenum, or some other steel alloy.