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The homebrew tandem

Before I arrived, Fredi sent me a picture via WhatsApp of a pile of old steel bicycles. He wanted us to weld a tandem together during my stay and I have to admit that I wasn’t sure if I liked the idea or not. From my experience in Switzerland, it is much easier to buy a second-hand tandem and repair it than to weld one from old frames and buy parts to put it together. What I didn’t know at the time, is that with a lot of improvisation, a bit of persistence and a Fredi who doesn’t want to spend a lot of money on the project (at least from a Swiss perspective), you can get a nice result that works for the most part. Besides, I learned a lot that will be useful for future welding projects and also for the bicycle design and construction course I will do in Madrid.

The first step of the project was to disassemble the bicycles in the pile and check which individual parts were present. We decided to use two low quality frames with heavy round tubes. In fact, all the bikes were cheap models, so any of them would have been suitable for welding, as cheap bikes usually use thick-walled tubes, which are less prone to failure and completely inexperienced metalworkers. After disassembly, I used the angle grinder to remove the rear end of the front frame and part of the head tube of the rear frame. As I expected, the split head tube of one frame fitted perfectly onto the seat tube of the other. Satisfied with this connection, I spent some time shaping and filing a thick galvanised steel tube that we planned to use as a down tube to connect the two bottom brackets. Thus the two frames were ready for welding and all that remained was to work out how we were going to mount the rear stem for the second handlebar.

The first mock-up of the two frames

After an exchange of opinions, Fredi had already half-convinced me that it would be better to weld the handlebars directly to the top tube of the rear frame. But I had found that the seatposts were one inch in diameter and it would therefore be quite easy to convert two old stems into a double stem with “two heads” to attach one side to the seatpost and the other to the handlebars. In the end we did it this way and the result is not really impressive, but it holds.

“Workshop” in the village

From that point on, several things happened in parallel. I spent two days in the village (because the generator does not provide enough power for the welding machine) trying to weld the prepared connections without producing too many holes. Fredi searched for parts on Wallapop (the craigslist of Spain) and got two white BMX handlebars with one stem and two white tyres. Welding was quite difficult as I don’t have much experience and initially worked with a machine that didn’t go below 200 amps. But I managed to create joints that look quite stable, even if they are very unsightly.

Fredi also practised welding with the connection of the two stems and after a coat of cheap green spray paint, I set about assembling the tandem with his help. With some creativity and punk engineering we managed to assemble and test it. At this point it only had one gear and a front brake. What was still missing was a mechanism to tension the front chain between the two cranks and long cables for the rear brake and gears. Fredi got the cables from the city, and the chain tensioner was a particular challenge, which is still not 100% solved. First I tried to put a big chainring between the cranks. I’ve seen this technique on homemade bikes before and you can find examples on the internet under “ghost ring”. It works well if you have a suitable chainring, but of the remaining chainrings in the pile, none were big enough, so the chain and chainring fell out several times on a long ride to the next village. A few days before I left, we experimented with parts left over from the dismantled bikes and eventually fitted a rear derailleur cage with pulleys around the chain. With a bit more punk engineering, it worked pretty well and the chain now mostly stayed put.

The complete tandem

Just before I left, I wanted to show the tandem to the new Workaway but one of the cage bolts came loose and we lost it. I put on a smaller pulley that I found, but it doesn’t work as well anymore. Let’s see if I go back to ARREA (with some tools I was constantly wishing for) and fix it one last time.