Building a tandem frame
 

I need a tandem and the only way I can afford it right now is to build it myself.
I am really starting from nothing here so will try to use this thread for others that need to get a tandem rolling ASAP w/o much cash. I hope to keep the total under $100

After a week of calling every bike store in town, craig's list, and freecycle I tracked down a guy that had a rock hopper and some similar frames that he gave me. OMG! They have 3 piece Cranks so I can put in nice BBs, that was a must. I have an ultegra and Dura-Ace take offs from my Land Shark that have very minor water pitting from years riding in Ore. Then again I only have one set of cranks that fit those BBs and 4 sets of square drive. Hmm, well Square BBs are cheap I think... I have one I can rebuild and one came in the frame that I might be able to rework.

The frames are not luged which was the hardest part of finding frames. You need this so you can change the tubes around and have something to weld to. I will be cutting the bottom tube off one and making that my center bottom tube. The other angles look pretty good other than the rear seat stays. I need a max seat tube length of 14" for my 7-year-old. The frame is 16" This means I will need to lower them.

Now the question. Should I cut the seat says off on both ends and re-weld or just cut at the seat tube ends then heat and bend the tube near the dropout to get the 2" of lowering? It looks like there will be enough length in the stays and if needed the front bike has longer stays.

Will add pictures in a bit.

I had to buy a grinder, a pack of grinding wheels (Flap, grinding, cutoff), A square w/ angle thing like a protractor. I already had the tools for removing cranks, and BBs and other maint. stuff.
So far money spent $34

Wouldn't you know it the grinder wheels I drove all the way across town to get are the wrong arbor size. I had the right ones in my hand and the "helpful" salesman showed me a better deal. :twitchy:
Only 16 miles out of my way on tomorrow's 30 mile commute but Google says there is a bike trail going that way so something new. Wish me luck.

At first I thought this sounded like a nutty idea, then gradually I began to realize that you might actually get this to work. It would be fun to see pictures. One thing that you might have to solve is getting the proper distance between chainrings so that the chain is just about right (not too slack or tight). Have you figured that part out yet? I guess if you were really careful you could build in just the right distance between bottom brackets. This actually sounds like a fun project. You might consider fillet brazing instead of welding so you can re-do joints that don't come out just right.

Quite lot of people have tried this, here is one:

http://sheldonbrown.com/tandem-build.html

it will bust the budget, but there is an eccentric bb that fits in a regular bb shell

I finished removing all the parts but the fork and here is the first picture.

http://lh5.ggpht.com/_thDShfGzeUg/TK...0/IMAG0169.jpg

Will have to pick up the right grinding wheels tomorrow and start removing tubes so I can get a better idea of things like bottom bracket distances and if I need to change the angle on the rear top tube so it points at the center of the head tube.

@sdold I am nutty and was going to do this in bamboo but time is short. I will be fillet brazing w/ MAP. Never brazed with anything but oxy/acc so that may be a challenge, may have to seek out someone with a setup. I have thought about the chain thing quite a bit. I will be running a right side chain on the outer rings so I can use the smaller rings of the triple in the rear. This bike will be towing a Burley trailer with 2 kids. Not many hills on the route but one has a hard pitch. I don't see making it over 17mph so I should not need a big ring. Most of the older tandems I see have an idler pulley on the bottom of the front chain. I may go this way with a derailleur wheel and a small adjuster.

I did the same thing. Very easy, I finished in a few hours. This are my pictures.

Two Canyon frames.
http://media6.dropshots.com/photos/5...708/125856.jpg

One Tandem frame
http://media8.dropshots.com/photos/5...720/163637.jpg

In the first tour, fully loaded
http://media6.dropshots.com/photos/5...002/124830.jpg

Got home late from work so did not get much done today. Deadline is Tuesday but I have all the parts but a front wheel so I think I can make that. Racked up a little over 50 bike miles exchanging the grinding disks today so a bit worn out as well. On the way home I picked up the brazing rod and flux. The rods stuck out of the top of my backpack about a foot and a half, got a few strange looks.

I did manage to get some of the tubes cut and now know there is plenty of bottom tube. I am going to leave the rear top tube as is. Both seat tubes are 73 degrees and the head is 71.

http://lh4.ggpht.com/_thDShfGzeUg/TK...0/IMAG0170.jpg

Moving on...
Got the old welds ground off and started cutting and mitering the new tubes.
I used my handy line laser to get an accurate cut line on the rear top tube.
http://lh5.ggpht.com/_thDShfGzeUg/TK...0/IMAG0175.jpg

Some fantasy work with the 1/2 round file on the boom tube to accomodate the front seat tube.
http://lh4.ggpht.com/_thDShfGzeUg/TK...0/IMAG0178.jpg

Fits just right
http://lh3.ggpht.com/_thDShfGzeUg/TK...0/IMAG0180.jpg

A quick mock up
http://lh6.ggpht.com/_thDShfGzeUg/TK...0/IMAG0182.jpg


I am going to weld the everything together before dropping the rear seat stays in the hope that it will be easier to keep everything straight. This brings me to the next hurdle which is how to check that everything is perfectly straight from the front fork through the BBs to the rear dropouts. I may go buy some angle iron and clamp it all together. Then again I may tack weld it and then draw out the frame on the floor for alignment. I would use some wood but don't know if I can find anything that is perfectly straight.
Any ideas?

Welding, what a fiasco! I could tell the small pencil flame of cheapo torch was not going to do anything short of starting my barbeque so off to the hardware store. I got the Bernzomatic ts8000 their hottest, fastest torch. This would get the tubes hot but failed to reach adequate temp on the BBs. I tried bricks and heat shields but not luck. Fortunately the auto starter only worked once and then failed so I had no problem exchanging it. I found the next step up and $20 more for one with oxygen. It said it would weld 1/8 plate and the gas lasted 45 minutes of constant welding. This looked promising. I got home and fired it up. Finally something that felt like a real torch flame. The regulators were a bit flaky but once I got just the right mix I could lay in some good filets. About 15 minutes in and 1/2 done. The Oxygen ran out. Must have been one of those package deals... Back to the store, the cylinder I got was not quite as big but I figured it must be full. Back to work, I had about 80% of all the welds done and this one ran out in just over 10 minutes. WTF? Reading the forums even watching youtube people are not having this much trouble. Could it be the chrome-moly or the altitude (6000ft)? Any how that one went back as well. I had everything set just like the instructions and did not get half the life they claimed.
My conclusion, Don't braze if you don't have an oxy/acetylene kit.

Next weekend I think I may try MIG, wish me luck on that. Once again I have never MIGed with a welder that was not a 220 Miller. This will mean grinding down the welds, etc what a pain. I will be going bamboo and carbon fiber on the next one. Home welding is just not what it is cracked up to be on the sales floor.

I did feel the welds are strong enough for riding and we have a roller.

http://lh4.ggpht.com/_thDShfGzeUg/TK...0/IMAG0185.jpg

I will build a bracket for the link chain idler tomorrow and hang some brakes and shifters. We did a few laps in the neighborhood and it rides well.

Today we built the bracket that holds the little idler for tensioning the front chain, hung some brakes and took a ride. Not bad for a weekend's work and $50.

http://lh3.ggpht.com/_thDShfGzeUg/TK...0/IMAG0187.jpg

Congratulations, VS. I must admit that when I read the begining of this thread I didn`t give you any odds of finishing it. Here`s a thought to consider if you want it. It looks like you left the rear seat tube long and your daughter appears to be kind of stretched. If you put a set of crank shorteners on the back cranks, it would effectively shorten the seat tube. Actually, you might be able to get very short double (maybe even triple) cranks from Gaerlan and a few other oddball bike stuff suppliers for less than crank shorteners. Anyway, have fun with your stretched limo.

I have been collecting free parts when I can find them so I built crank shorteners by cutting and tapping an old set. That saved $100!
http://lh6.ggpht.com/_thDShfGzeUg/TL...4/IMAG0192.jpg


All together I now have around $100 into the bike including the new tires. Amazing what you can find at bike stores for free. About another $100 in tools. This included a welder, grinder and drill. I already had all the tools for pulling cranks and replacing BBs among other things. So i would say that if you look really hard for the parts it is certainly possible to build a tandem for $100 depending on the tools you have already.
Here is the finished bike, You can see that I moved the chain to the other side so I could have 3 rings on the cranks. I also improved the idler which is made from the front clamp on dérailleur and the bottom of a rear. Next trip to the LBS and I will pick up short chain ring bolts. Those of you with a good eye will spot the titanium shaft speed plays, yes I know those are more than 3X the cost of the bike. I borrowed from my Land Shark for those and the aero bars.

http://lh4.ggpht.com/_thDShfGzeUg/TL...4/IMAG0194.jpg

I love this so much. Great work, given the 100$ spent.

Congratulations!?? Finally what did you use to weld? did u finally braze the bike or tig welded it?

Looking good, VS. I really like the tensioner on your timing chain- the chopped derailler jockey looks very cool.

Ummm... do you have them pinned or something so the little stubs can`t rotate, or just bolted through the end pedal holes? I don`t see anything in your pic, but maybe there`s something that doesn`t show up from the camera angle. It sure sounds like a good idea to have something besides one bolt keeping them from rotating. Even a pipe clamp would probably do the trick.

I put a small steel pin in there to keep the shortener from turning, you can't see it at all.

I also ended up using a Bernzomatic Oxy/MAPP gas setup with a simple propane pencil torch for preheating and to add heat to the BBs. This torch will get the job done and is cheap $60 compared to the $600 it would cost for a "real" torch. I was able to do some fair fillets but it took two more O2 tanks at $7. I was really on the fence of going to a flux core mig on sale for $89 at HF but I also need to do some moving around of the brake cable braze ons. Because I only plan on doing this frame and then switching to composites like bamboo and carbon fiber I did not want to put much into the torch.

Today we cleared the 200 mile mark and everything is working perfectly. I still need some wheels with bearings that are not pitted and a new BB for the front. So the will be some more costs in those, maybe $95, but wheels will go on other bikes and are some what of a maintenance item anyhow.

Nice job! As long as you are happy with the quality and strength of the fillets, that's a cool bike you've got there. I'm seriously impressed.

I love stuff like this. Very cool build!

To velosprinter, great job. I have the same torches plus a couple extra. I like that you did the job without a fancy frame jig. Thanks to whoever moved this post to framebuilders.