[febikes]

Guys,

I am on the road to building my first bike and really enjoy the tips from everyone. Big thanks to Walt for all the stuff you do and for sending me the box of sample tubes ends for weld practice. Also big thanks for everyone else for tips and such.

One area that I have not seen discussed in detail is safety factor. I am building out of 8/5/8 main tubes and will be using a 9/6/9 down tube for my first build. I am learning welding along the way. I am also doing/planning the build in steps (i.e. seat tube, chain stays, seat stays, and then down tube with the top tube as the last tube I will weld on. After each tack weld I am alignment checks and also doing the occasional second pass on one side of a weld to maintain alignment.

In any case my big concern as I get closer to the head tube welds is safety. My view (could be wrong) is that a weld failure in the rear end will not generally cause injury. Weld failure in the head tube is more of a concern.

Other then the things on the learning TIG thread does anyone have thoughts about safety and/or stories about how bikes built by newbies typically fail. In particular for those of you who like me went down the self taught road how did your first bike fail.

Thanks (and sorry for so many words)

 

[Brad Bedell]

Not really frame specific, but the two places your weld may fail. (assuming you use the correct end of the tube)

1. Not enough penetration
2. Too hot.

Sure, a dirty weld or poor miter would be an issue, but I think you've got those mostly covered from your other threads. The challenge you'll have with learning to weld is the difference of material thickness. It will take a bit of a learning curve to control the heat between the materials. You'll get some practice welding your bottom bracket. Although, I might go to the local muffler shop and pick up some scrap 1.5" .065-.080 wall tubing and weld your lighter gauge to it. If you accidentally cook the lighter metal, you might have the tubing break on you. In either case, keep a close eye on things near the welds. I've never seen a 'decent' (Externally, yours classifies as this from what I saw on your blog) weld fail without "some" warning first.

One good 'test' on your weld is to cut the tubing apart and look at the inside bead as well as a cross section of the bead. You'll see if you get good penetration or not this way.

The one weld I had fail on my TI bike I built a few years back was from not enough penetration at the bottom bracket. After that failure, I disassembled the bike, cleaned and set up the back-purging again, and did two more passes on the entire frame. Afterwords, I put close to 10k miles on it with no problems.