myhomemadetandembicycle

The frame: I was lucky enough to find two 4130 chromoly frames at the local thrift store that matched my wife and I in size pretty well. The front frame is a 23" and the rear frame a 21". It is a pretty tall bike, but I like the way that it rides. 4130 is a good way to go if you can find two frames that are the right size since it is relatively light and very strong. It is also really easy to weld. The seat tube on the front frame and the head tube on the rear frame matched up in angles pretty well, so that made jigging the two frames together all the easier. As a note, I kept all of the parts I stripped off of the bikes to be used later in the process (hint- use ziplock bags). I also used a piece of one other bike as a support beam as you will see later. Cost= $24

Welding the frames: I am lucky enough to have a brother-in-law who has a welder and was able to do this part for me for free. TIG welding is apparently best, but he only has a MIG welder, which will do a more than effective job. I basically just cut the head tube open straight down the middle and matched it up with the seat tube of the brown frame after cutting off the upper chain stays. (note: all of this is a lot easier if you have saws and grinders and the like- but a hacksaw will work if that's what you have) Then I clamped it with some vice grips to hold it in place. I put the tires on at this point in order to make sure that the bottom brackets were both the right distance from the ground (about 11.5 inches from their center to the floor). Then we welded those two pieces together and then welded the top bar from another bike between the two bottom brackets for added support. Make sure the two frames are lined up straight, you can do this with a piece of string wrapped around the two frames, ensuring that the distance is equal on both sides. Eye-balling it works as well and is nearly as accurate. As you can see you will end up cutting the entire rear triangle of the front bike off. It is also a good idea to sand off all of the paint around the areas you are welding. And there you have it, a custom tandem frame. Note that the stoker (person in the back) is pretty close to the person in the front as compared to traditional tandem frames. Thus the stoker will need to be a smaller individual or someone who likes to ride in the upright position. Be careful when welding the two frame together to not damage the bottom brackets or seat tubes. I ended up having to grind off parts of the front seat tube where the welding had bubbled inside. Cost= $0

Sanding the frame: Here you have the option of just roughing up the original paint or actually taking all of the original paint off. I went somewhere in-between and sanded off the paint I could with a wire brush attached to the device shown in the picture. I roughed up the rest as well as I could with sand paper. I didn't want to spring to have someone sand-blast it for me, but this is probably the best method. Cost =$0

Here is the frame when I had it sanded down and ready to paint.

Painting: Next job was to paint the frame. I researched lots of different types of paints and processes, and decided to go with the cheapest and most durable I could find. I decided to use Hammerite, which is a metal-specific paint that is strong and doesn't require a primer coat. It is also a good rust protector. It cost about $8 a can and I got 4 light coats on (which is recommended) with one can. I used rolled up newspapers to protect the seat tubes and bottom brackets and put masking tape around anything esle I didn't want paint on. I put a seat and post into the front frame and hung the bike from my homemade bicycle repair stand (I didn't care if it got paint on it). I did the painting on a relatively cold day (about 40 degrees) and I may have lost some quality to the paint job for this reason, but I didn't have anywhere else to paint it, so I just went for it. I brought it inside to dry by the furnace for two weeks before beginning to build up the bike. Seems to hold up pretty good though as far as I can tell up to this point. Cost= $8

The drivetrain: This was one of the more challenging tasks of building the bike, but it worked out great in the end. I followed John Allen's advice on this section. I got a regular triple chainring (48-38-28) and bolted a 44t chainring to the outside of the largest ring. This took some ingenuity before I got it right. I ended up using washers from the hardware store to space the outside chainring (for the sync chain). It barely fit in the space allotted between the outside ring and the crank arm- but in the end it worked. I also had to get some longer bolts to hold together the new configuration, which Mad Dog Cycles had on-hand for a good deal. Only relatively newer crank arms have the required space to add an extra ring (even though mine weren't that new really). For the front crank I attached an identical 44t chainring to the crank arm and spaced it out an equal distance with washers so it lined up straight with the rear sync chainwheel. Cost = $30

Assembling the bike: At this point I just had to assemble all of the remaining parts onto the bike. Most of these I got off the of the donor frames and also used some old parts I had lying around. I did buy new chains ($35) and new cables and housing (about $37). The sync chain worked by adding an extra six or seven links the bike shop gave me to a full chain, plus the links I took out of the rear chain. I also had to get new handlebar grips ($6) and buy a stoker stem to attach the rear handlebar ($20 via ebay still in transit at the time of the picture to the right).

I decided to start out with the pedals in phase, meaning in the same position front and back.

Routing the cables was a bit of a challenge, but in the end I was able to use the existing cable routes and the shifting ended up working wonderfully. Make sure your donor frames are going to have the necessary braze ons and keep any cable routing guides (such as those that are on the bottom brackets) as they come in handy during this part of the job.

I didn't end up using any chain tensioner for the sync chain since it seems to have worked out perfectly. The teeth on the sync chainrings are pretty deep and grab the chain so I don't think it will ever come off. I had a hard time taking the chain off manually to put the cranks in phase, so I'm not worried about coming off if I hit a bump or something. Cost = about $100

Total Cost = about $165

All Pictures

Did you enjoy learning about this do-it-yourself project? Email me with an questions or comments. Also visit Sheldon Brown's page on building a home-built as well as John Allen's for help on the crankset.

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