Need one for a North to South Wales ride in September with my work. We've plenty of old steel bikes to canibalise, but hints/tips/plans/photos would help lots for our build.
We're also considering a trailer with seat for the "cox" to allow a 4th man in rotation with the driver and two stokers. Has anyone done a mansize version of a kiddy trailer?
http://www.sheldonbrown.com/tandem-build.html
One day I will have a go at that.
Keep us posted eh, sounds great.
A
lol
Its a tridem or tandem triplet. Thorn do one, they are interesting to pilot to say the least
There is a guy in the states who races offroad on one with his twin sons!
Seriously if you are going to build one you need to consider how you can get the strength into the frame and tension the chains. You need to do more than just weld a few old frames together to get the strength
Brakes and wheels are the other weak area
There is a Quandem in a shed at my work ! They wouldn't let me ride it tho, perfect team building exercise if you ask me, what with no brakes and all.
I have.
In about 1980 I put an ad in the local paper asking for free bikes. I got loads of replys and collected a two gents bikes and a woman's frame. I put the biggest one at the front, the next in the middle and the woman's frame at the back. I cut the chain and seat stays off the front bike then sawed vertically through the head tube of the next frame. Repeat for back frame. To keep the frames in alignment, I got some 4x2 and laid out on a flat surface put the frames on top, put more 4x2 on top and weighed it all down with concrete blocks. G-clamped the frames together - the cut head tube butting up to the seat tube of the frame in front. Then I cut up an old garden swing and used the legs to connect the bottom brackets. Then I brazed the whole lot together using an arc welder with carbon rods.
For the drive train I used 10 speed front chainsets on the right hand side of every frame. From the front, the inner ring was connected to the inner ring on the middle frame and the outer ring of the middle frame was connected to the outer ring of the rear frame. The inner ring of the rear frame was connected to the rear hub. I used frame mounted (bodged) tensioners to keep the chains tight.
Rear rider had control of gears and rear brake! Driver only had steering and front brake.
The biggest problem was that it wasn't nearly stiff enough as I didn't have access to suitable tubing and probably because I brazed instead of welded. Frame flex eventually became terminal but not before I offer a lift home to a drunken mate on New Year's Eve failing to mention that we had to cycle home 7 miles on the Trandem.
No pics as only have film photo somewhere but it was good fun.
Good luck
Tony Oliver had a book called Touring Bikes which had some information on building / designing tandems, which will apply to tandem triplet.
I put an email round work asking for donor bikes. Within a day I was inundated and now am the proud owner of 12 more bikes 
I have selected three to be the main donor frames, including a particularly retro Apollo moon bike (as in - would be appropriate for the reduced gravity found on the moon).
Now time to get to work with the angle grinder and mig welder - bring on Frankengriff's monster!
Right then, old bikes are stripped and frames are ready for surgery. I'll post pics when I get a moment.
The spirit of Sheldon lives on in you sir. More power to your mighty elbow
Even my boss is coming on the 220 mile ride "just to see the trandem fall apart and see me have a nasty accident". He doubts the structure will be adequate - I have more faith in my design capability.
We're both Chartered Engineers.
Scaffold pole each side for extra strength?
Scaffold pole each side for extra strength?
No, hinge in the middle like a bendy bus. 
Looking forward to the pics.
I've had a pair of Bombers donated that I may use.
Comments on 'owning' people aside, shoud I use them and pump them up hard, or just use rigid forks? The bombers do open up the opportunity to use a front disc brake.
*no responsibility is accepted for the quality of this advice*
Normally I would say a disc is essential - but will the headstock be strong enough? I am not sure which is more dangerous - inadequate front brake or too powerful a brake on a flexy frame.
Rigid fork I guess
I've decided to measure up the frames and conduct a full 3D finite element model of my proposed frame, together with a dynamic analysis and look at the resulting stress concentrations. Then weld in big **** off stiffener plates in these areas 
Sounds like a plan. I vote for cut up dexion shelving for added homemade effect
1111 off here built this contraption:
it was pretty interesting to ride!
and I'm sure it could be extended with another bike...
I Found some pics
Its the sort of thing that made Britain great!
Hi Dan, I think I know where you work LOL!
Anyone stump up some frames?
i have been seriously (and seceretly) thinking about building a mtb tandem. i have a access to welding equipment and tubing and lathe etc. i may give it a go when i get back from the falklands. will keep people posed on the progress.
Not quite a tandem, but currently building a long-tail to transport me & my boys (aged 2 & 4) on nursery / school run.
Using nice stiff alloy GT H/T frame for the front & Kona HT rear triangle at rear.
Try searching on Flickr, loads of pics on there of such conversions. Biggest hassle for me has been rear brake hose.
Santana in the US make them.
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That should give you some ideas for frame proportions.
But hey why stop there, go nuts!
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notes on frame tube sizes
http://santanatandem.com/Techno/FNCroMoly07.html
• 32mm unpierced top- and lateral- and seat-tubes
• Conical 35–44mm down tube
• 60x40mm ultrawide oval bottom tube
• 35x23mm oversize unindented chainstays
1111 - MTB tandems are very overbuilt - no standard components in the frame at all - mine has a boom tube over 60mm round for example.
If you are cheap like me ,you could do this!
tj. i was going to build it out out of 30x30 box section.
but then again i saw on crc they do a frame for £400
Backhander - yes, 13 frames offered and still counting. South Wales Police may also be donating a fair few.
Some chaps from my neck of the woods
1111- i was going to build it out out of 30x30 box section.
that wouldn't be stiff enough for a tandem. 60x60 would take the bottom brackets nicely
Jack Taylor and Tony Oliver suggested / used forks with around 65mm offset. This was to help make the tandem/trandem more stable / less prone to violent change of direction when riders move their weight around.
I do hope that you will follow the spirit of Sheldon in riding style as well as bodging building techniques and ride it like him
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