Rear triangle complete

November 30, 2009 · 4 comments

rearTriangleCompleteIt took quite awhile but it is brazed and ready to fit to the front triangle. Fitting the tubes took a lot of time with my limited tools. It isn’t perfect but that is not the point of this exercise. I’m experimenting with this bike design to try and solve the weight distribution problems. I’m also using it as a learning exercise for bike fabrication. Here are some things that I discovered.

Tube fitting is hard to get right with just hand tools. It takes a lot of trial and error to get the many curves and angles to fit together. It is critical that they fit without large gaps so that they can be brazed. Someday I will have a mill or a tube notcher.

seatTubeWeldedWelding provides many challenges. I spent a great deal of time reading up on all the techniques and material combinations. There is a lot to know in order to make good strong welds safely. It is critical that the welds are strong and won’t break. If the bike breaks apart while riding at high speed, injuries are likely. Since this is an experiment and I’m still learning, no one but me will ride this bike. If you are going to be doing this for yourself or others, don’t rely on my advise. Take a class, read, learn how to do this correctly and safely. There are more hazards than just the strength of the weld. There are explosion hazards as well as toxic fume hazards. Make your own choices; I am not responsible for your actions.

seatStaysWeldedMetallurgy is an interesting topic. There are many variables to consider when choosing metals, filler materials and welding techniques. Some of the information is contradictory which makes it even harder to choose what to use. I won’t go into all of that now. I chose to use the traditional brass rod with flux and fillet brazing as described by Paterek. The fillets seem be be very strong but I won’t know if they will hold up until I add all the weight.

Many bikes are fillet brazed using brass rod with flux. Here is what I used for this project: Gasflux C-04 brass rod 1/16” and Type “B” paste flux. My torch is a Smith AW1 with AW203 tip.

setStaysCleanedThe alignment of the fabricated tubes was fairly easy for this part of the project. I used a tape measure to get everything lined up. Heat distortion caused some of the alignment to change from where I had it set. I don’t think this will be a problem for the rear triangle. This could be a major problem though when fitting the rear triangle to the front triangle. I’m going to have to build a jig to keep it all in line. Just using a tape measure and string isn’t going to cut it.

What’s next? I’m going to build a jig to hold the front and rear in line, fabricate the other tubes needed to connect the front and rear, weld it all together. A new camera arrives this week so stay tuned for more videos.

Click on comments below. Let me know what you think. Ask any question. Tell everyone your techniques or how to do these things better. Share your opinions.

{ 4 comments… read them below or add one }

1 Kate December 1, 2009 at 11:26 pm

What is that oozing gold tone substance? This looks like bike alchemy to me. How do you manage the fumes from this process without passing out?

2 Dan December 2, 2009 at 9:14 pm

Hi Kate,
Isn’t that a nice gold color? The material is brass from brass brazing rods that I got from Henry James Bicycles. A lot of custom bicycle frames are fillet brazed using this material. The tubes are heated with a gas torch to the point of melting and the brass rod is fed by hand into the pool of molten metal where it melts and creates a fillet which is basically a lump of brass. This holds everything together.

Good point about the fumes. There are some toxic fumes produced. I use good ventilation and wear a mask with filter canisters as a precaution.

3 Kate December 2, 2009 at 10:57 pm

Well, that’s a relief about managing the fumes. How strong is welded bond? A bike can take a beating – will the frame hold up under the wear and tear of commuting and with the added battery weight? I’m still thinking about weather an electric bike is right for me.

4 Dan December 4, 2009 at 9:47 am

Regarding which bike is right for you depends on many things. I’m planning on providing more information about this in my newsletters. If you haven’t signed up already, just go to the sidebar to the right and enter your email address. I include information in the newsletter that may not appear in the posts in this column. If you have specific questions, send me an email and I’ll try to help.

There are many variables in how the frame with welds will hold up. I predict that the way I’m doing it here will be plenty strong because I’m using extra tubes under the batteries. Plus, the additional tubes are thicker than the existing tubes. Another factor in frame strength is the geometry. Triangles are very strong shapes. Since the extension for the battery area is not a triangle, I may have to add a gusset which is basically a small triangle piece that fits in one or more corners where the tubes join. This project is an experiment so we will see how it holds up.

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