joepaiva

Years ago, I built bikes (but not frames) from old parts. It was huge fun, but then life got in the way (school, job, etc.) 30 years later, I am starting to build frames/bikes again for fun. Now though, my goal is to build side by side tandems and velomobiles that my wife and kids will actually ride in with me.

So here is my first newbie/old man (the times have changed) questions:

- I can do the math and calculate bottom tube sizes, but does anyone have any "real world" experience or rules of thumb for sizing 4130 bottom tubes for LWB recumbent bikes? Stiffness will obviously not be an issue for a side by side tandem going 5-10 mph around the neighborhood or down a flat bike path; I just don't want to add any more weight than absolutely required, but don't want to have a "bent bent" every time I hit a small bump in the road...

- It appears the entire industry is moving toward Carbon Fiber and TIG Welded Aluminum frames. However, being a newbie welder and planning on my first few prototypes to most likely be "flawed experiments", I am thinking it would make more sense to start out practicing with 4130 and a cheap arc welder (just to get my design right and welding skills up to snuff). Does that make sense?

I was originally going to go with lugged construction and brazing, but I can't get the flexibility of design I want using pre-manufactured lugs. Then I saw a cheap Flux Core Wire Welder on line that all the reviews say is great for all sorts of light duty welding. However, old threads on the welding forums said using MIG/Flux Core Wire on 4130 Bicycle Tubing was a really bad idea. So, now I am looking at a cheap arc welder (from Harbor Freight). Here are the issues and related questions:
- The way the local community college does classes, I need to finish the brazing course before the MIG course and the MIG course before the TIG Course, meaning it will be months before I can start TIG welding with any sense of knowing what I am actually doing). So, would using the Flux Core Wire Welder really be that bad just for low speed, low impact, prototype building?
- The way the forums describe TIG welding (i.e. incredibly difficult to do well, get cancer from breathing the gas, etc.), would I be better off just using bamboo or something for prototypes and then laying up carbon fiber once I get the design correct?

Thanks in advance for any help/advice,
Joe P.