Since (a bit more than) one year, I had a big issue on my bike: the frame was broken! Despite that I didn't find somebody to weld it, I found an introduction to arc welding.
Is welding a good solution? Does it "just work"? Is it fair? This blog post is a small recap about what to do if a frame broke and a time capsule to see how much time a welding quickly done will resist.
Welding reminders
Welding usually consists of heating two pieces usually made of metal, making them melting, and make them fusion via capillarity. Some techniques do not involve metal (as some ultrasonic one). Some do not involve melting the material (as cold welding). However, here, we will only speak about fusion welding on metal.
The majority of welding methods need the addition of another metal. In electronics, we frequently add tin. In metal fabrication, we can add brass or even a mix of multiple metal. Each technique has its own specificity.
When the welding is done with electricity, the temperature will be provided by the intensity of the current, thus "the quantity of current". In some welding control, we can find the "current power" control. Of course, it will change the intensity of the current (P=UI, with P the current power, U the current tension and I the intensity).
This temperature will try to be propagated inner the metal via heat conduction. This means that if the temperature is too low, our metal will not melt. Else, if it's too elevated, we may melt some zone that we don't want to weld, and this includes an existing weld.
Repair a bike frame
A bike frame is made of the following parts:
- The head tube and the fork;
- Top tube, in the top;
- Down tube… At the bottom of the frame;
- Seat tube, in which the seat post is inserted. It maintains the geometry of the frame.
- Seat stays, at the back of the seat post;
- And finally the chain stays, at the bottom, between the pedals and the rear wheel.
Figure: Schema of a bike frame with part names, by authors Keithonearth, Original author: Al2, from WikiMedia.
Please note that the description is generalist and may change following the type of frame you have.
If the front of the frame is broken, DO NOT TRY TO FIX IT! Indeed, trying to hit the road, you risk eating the road. If the rear of your frame is broken, the biggest risk you take is to break again your bike.
For the welding, we will insert in the broken tube a base. This latest aims to retrieve and keep the geometry of the frame. Moreover, it will reinforce the welding.
My bike
My bike is a MBK Java. It has a step-through frame. This means that the top tube join the seat tube under the seat stays, very near the down tube junction.
Figure: A MBK Java, used by the courtesy of Canalcycles.
In my case, the seat tube was broken between the top tube junction and the down one. The geometry was enough affected to have doubt about if it was possible to repair it.
I wanted to repair it because it was an old bike and I attach value to old objects. Moreover, it was also to learn welding. Finally, I always prefer repair, even if I have to learn something I do not understand, instead of throw and buy another item.
The original welding was made via the within, using brass. That is why welding is not visible. However, because the melting temperature of the brass (930 °C / 1710 °F) is less than the melting temperature of steel alloys (usually more than 1000 °C / 1800 °F), we had to be very careful about temperature.
Figure: Original welding of my MBK Java.
Figure: Same kind of welding seen from the inside.
Figure: Cleaning during the welding.
Finally, we had a small welding incident at the end. The temperature was too high and melt a small piece of the top tube. This is, of course, a standard incident and the hole has been filled.
Figure: The hole created during the welding.
Figure: The completed welding.
Is it fair?
Is repairing the frame of their bike fair? Currently, I don't know. The best I can tell is that we repaired my frame the 4th of October 2022 and currently the welding is not broken.
I will update this blog post when it will break again.
Thanks
- Corrado, for teaching me how to weld using a MIG, and for helping me repair my frame.
- The Cyclofficine, a self-managed repair shop in Paris.
Highlight
Some time ago, I decided to highlight "lesser known" artists on my README files and blog posts. This is a gift for curious people who find these texts, a digital time capsule of sorts!
For now, and because of my current life and mood, I don't yet know who to highlight. I'll fill this section when I'll update this post.
Note about what have I learned
By doing this project, I learned basis of MIG welding and practice it.
Changelog
Edit on the 2022-11-04: Add a picture of a welding seen from the inside.