First bike build Gravel/Cross

[TheoMcD]

Hey all,

I'm working on a first bike of mine, which I am planning to be a steel gravel bike, but built with a bit of a race geometry, not that I race, but hey strava segments need getting after! Anyway, I've got a small home machine shop and a TIG welder from other interested, so it seemed like this could be a fun project! I started to work on the design in BikeCAD then attempted RattleCAD but I think I'm going to go with a more engineering style CAD program for the final design as I do similar type engineering at work. I'll keep a log here of how it goes and decision I make, as it might be interesting for some.

So before I get too far, I figured it seemed smart to work on some welding and see if I even have the skillset to attempt this project. I purchased some 4130 tubes from OnlineMetals, and mitered a few tubes in the mill to practice on. I'm really having a hard time getting the welds to look like some of the work that is showcased here, and while I know time builds the skill, I figured I'd ask if there was any advice for what I'm doing based on the some photos of the work. I'm using a Miller Diversion 165, flexible #5 head, 1/16" Tungsten with a #5 or #8 cup if its tight with new .035inch dia ER70s2 filler wire. Here are some photos of the welds, my general guess is I'm going too slow and putting too much heat into the part. My max is current is about 40amps with pedal all the way down, so usually less than that. All tubing shown in the photos are 1in or 1.125x.035. I welded a 24" piece on a 1.5x.065 tube as a seat-tube to Bottom-bracket test, where I planned to break the joint to see where it broke, so with a 4 foot moment arm with cheater bar and all my weight hanging on it in the vice I cant break the weld, though I'll figure out a way and show the photo of it later.

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First welds look okay.
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The Photo above is a 45deg miter. I think the best weld I have done was in the limited access section. This was done with a #8 cup.
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This burning inside of the tube gives me the impression its a full penetration weld, though I'm concerned that this also shows too much heat. I'm not back purging any of these components at this stage.

Any tips greatly appreciated.

Theo McDonald
Central TX

[adarn]

Hey Theo,

That's rad that you are building a bike.

Your welds look better than my first welds, but I will give you a few tips.

First, you should clean the tubes more before welding. Try scotch-briting till they're shiny then clean them with alcohol or acetone.

You are running hot, but I think this is mainly because you need to add a lot more filler. You may have better luck with a .045 filler. I would also go for a bigger cup. I like my #10, make sure you are using a gas lens as well.

Also, everyone welds differently, so take it all with a grain of salt.

Have fun!
Adam