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Tandem frame

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Old 03-08-18, 11:22 AM
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Tandem frame

If one wanted to build a frankenstein tandem out of a couple of frames, are their any plans online as far as ideal angles, tube lengths etc go?

Or could you just rig the 2 halves as if each rider were on their own bike?

6ft guy and 4.9 ft lady on back.

Are tandem frames usually brazed or TIG welded?
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Old 03-08-18, 12:10 PM
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Tandem frames are usually made with whatever process the builder feels more comfortable with. Just like any other frame, there is no particular advantage to one method of joining over another.

You need to make it so the stoker isn't too close to the captain. So repurposing a regular frame doesn't quite do it, it's too short. The top tube needs to be lengthened somehow.
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Old 03-08-18, 04:10 PM
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Search u-tube for diy tandems, tons of examples/how to vids there. They aren't frame builder works of art but apparently very rideable frankenbike tandems cheap(if thats what you're looking for).

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Old 03-08-18, 09:16 PM
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Originally Posted by unterhausen View Post
You need to make it so the stoker isn't too close to the captain. So repurposing a regular frame doesn't quite do it, it's too short. The top tube needs to be lengthened somehow.
So basically using old frames for the front and rear triangles of the tandem and then adding tubing for the top tube??

Strength wise, do you think it's better to totally cut out the old top tubes and chainstay tubes at the joints, or just put in tubes to join/lengthen it half way?

I'll check out YouTube.

Thanks.
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Old 03-08-18, 11:44 PM
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I probably would remove most of the stuff behind the seat tube of the captain and the seat tube of the stoker position, but a lot of people leave more than that. There have been some home made tandems, you might want to look in the tandem forum here.
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Old 03-09-18, 05:40 AM
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Good project, hope you'll post photos as you go along. There is a pretty comprehensive guide here on Sheldon Brown's site: sheldonbrown.com/tandem-build - sorry, I've not posted enough to include the full url but this should get you there.
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Old 03-09-18, 10:29 AM
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leave the rear wheel on the front bike, spread the fork on the back one, you said .. "build a frankenstein tandem out of a couple of frames"..
So.. it will have 3 wheels ..
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Old 03-11-18, 07:23 AM
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Originally Posted by eno View Post
Good project, hope you'll post photos as you go along. There is a pretty comprehensive guide here on Sheldon Brown's site: sheldonbrown.com/tandem-build - sorry, I've not posted enough to include the full url but this should get you there.
William.
Think i might be changing my mind as i learn more. LOL. There are evidently zero single seat touring bikes for sale in Phnom Penh bike shops let alone tandem tourers, and my girlfriend says she's not comfortable riding her own bike on the mad roads so just weighing up my options and also find this stuff interesting. The satisfaction of touring through countries on your own built frame!

As far as the tricky frame alignment go's for complete amateur builders - would lugged joints make it possible to get away without using a jig and enable you to align by eye and straight edges, plumb lines etc? Are the lug joints tight enough on the tubes to allow very little movement?
Say for example you used lugs on the most important alignment points of the frame, assembled the frame, aligned it by eye and string (without a jig) , and just made tiny removable tack welds on the lugs and then checked the alignment?

#PossiblyDreamin'
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Old 03-11-18, 07:53 AM
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First of all I believe that it is going to be difficult if you are even able to find tandem lugs, but as far as alignment it would be much better if you had a jig.
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Old 03-11-18, 08:10 AM
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Originally Posted by Brian25 View Post
First of all I believe that it is going to be difficult if you are even able to find tandem lugs, but as far as alignment it would be much better if you had a jig.
Doh! Yeah, didn't think of that. Totally different angles at the crank tubes i guess?

Just read this about how they used to build frames without using jigs. Evidently they just drilled tiny holes and pinned the joints in place and the brazed it.

Jigs only came into wide use in the 1960s, prior to that most framebuilders assembled and pinned the frame together by drilling a small hole through the lug and tube, and inserting a short piece of wire or small nail. The frame was then usually hearth brazed; that is a hearth of hot coals, or one made of fire bricks with the heat applied with a hand held torch. (Picture left.)

With hearth brazing there is less distortion because the whole joint is heated uniformly. For example, the whole bottom bracket shell, seat and down tubes, and in some cases, the chainstays are all brazed at the same time.

The drawback with hearth brazing is that you heat the tubes several inches away from the joint and thereby anneal or soften the tubes. The method I used was to braze with a hand held torch that had a smaller but more intense flame. Working quickly, I could pin-point the heat on the lug only heating the tube barely a quarter of an inch (6mm.) from the lug. This way the tubes retained more of their inbuilt strength, resulting in a stiffer more responsive frame.

Dave Moulton's Bike Blog: Framebuilding FAQs
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Old 03-11-18, 08:32 AM
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More ;

Pinning the frame alone will only ensure that the tubes do not slip in or out of the lugs, the whole assembly will flop around like a jointed wooden puppet. You will need to braze each pin in place, in other words tack it. Then you can check for alignment, and the tubes will move on the pin and tack and stay where you place them.
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Old 03-11-18, 11:25 AM
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Classic truss is a lot of triangles, so consider triangulation..



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