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Old 01-12-08, 12:01 PM   #1
ChiapasFixed
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simple jig for tacking

so im starting to design a simple frame jig for gluing my bamboo bike. i then intend to wrap the joints off the jig on a regular stand.
what are tha basic rules of thumb for setting up such a jig? It dosent have to be adjustable, id rather make it simple to build and re-build for every new frame.
anybody have any good designs? i mas looking at Brano Mereīs jig here:
http://www.bmeres.com/carbonframe1.htm
but it still seems a little excessive... couldnīt I just use a piece of plywood to fix the bb, head tube, seat tube and rear axle dummy?
how about just a flat table?
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Old 01-12-08, 12:22 PM   #2
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Arklatex on frameforum built this simple plywood jig.



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Old 01-12-08, 12:32 PM   #3
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great! thats what im talking about...
how do I fix the distances for BB and rear axle?
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Old 01-12-08, 01:16 PM   #4
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Originally Posted by ChiapasFixed View Post
great! thats what im talking about...
how do I fix the distances for BB and rear axle?
That's a good question with a very complicated answer.

You need to start out by making some basic size and geometry decisions like the top tube length and seat tube length, desired wheelbase, desired bottom bracket drop, and seat tube and head tube angles. The wheelbase will be determined primarily by the top tube length, head tube angle, fork length, seat tube angle, and chainstay length. Once you've worked out the dimensions and geometry, you'll be able to locate the BB and rear axle.

You can play around with the free on-line version of BikeCAD to see how different tube dimensions and seat tube/head tube angles affect the locations of the BB and rear axle, since they're all inter-related.

Bikeforest.com. Under the BikCAD tab, click on "Free Applets" and "BikeCAD".

Here's the BikeCAD output for my 61cm custom Waterford road bike.

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Old 01-12-08, 03:58 PM   #5
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"great! thats what im talking about...
how do I fix the distances for BB and rear axle?"

Do you mean, how do you design a bike? Or given that you have one you are copying already, how do you get that on your frame jig?

The former is a big subject. The latter, is just a mater of measuring the BB center down from a line drawn through both axles (tension a string), then measuring the rear hub distance from the BB center. With those two numbers you can measure the bb position down from the wheel center line on your jig, and use a compass from the center of the BB and the point it crosses on the CL to establish rear hub position.

You mentioned something about a single speed, so if you have a bike whose design you currently like, but want to make in bamboo, just use a compass and an inclinometer. Draw your BB, relative to your axle height. Then shoot a line up at the angle you want your seat tube to be. Get the angle and length from your model bike. Then measure from the center of the BB and the center of the seat tube top end, to the center of the lower end of your head tube. Measure the angle of the head tube. Along with the rear axle is all the info you really need. The precise position of every tube varies depending on how you are joining it, some methods need more space than others. But those angles and relative positions establish the bike's geometry.
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Old 01-12-08, 06:01 PM   #6
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im probably going to copy a frame that fits me, although i was thinking of making a 29er ss mountain bike frame, but dont have such a frame, so i will probably start by copying my IRO frame, then once i know i can make a frame, maybe design the 29er using bike cad or somesuch. thanks for the tips....
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Old 01-13-08, 01:31 AM   #7
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Good luck, sounds like a cool project.

Probably the simplest way of getting where you want would be to just cut up a bike, and use sections of tube at the joints as internal spigots for the bamboo, then wrap the outside with carbon and fair it together.
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Old 01-13-08, 09:02 PM   #8
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Good luck, sounds like a cool project.

Probably the simplest way of getting where you want would be to just cut up a bike, and use sections of tube at the joints as internal spigots for the bamboo, then wrap the outside with carbon and fair it together.
good idea if i had a broken frame or two lying around. maybe this could be a good way to recycle old frames, but for this project, i want to test the viability of this technology for applications here in southern mexico, so i think i will try to wrap the joints myself with natural fibres and polyester or epoxy...
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Old 01-13-08, 09:08 PM   #9
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Originally Posted by ChiapasFixed View Post
good idea if i had a broken frame or two lying around. maybe this could be a good way to recycle old frames, but for this project, i want to test the viability of this technology for applications here in southern mexico, so i think i will try to wrap the joints myself with natural fibres and polyester or epoxy...
Just a suggestion: make sure to miter the bamboo joints properly. Tubing joints, whether bamboo, steel, aluminum, titanium, or carbon fiber need to be properly mitered to achieve maximum structural integrity.
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