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Old 2012-05-18, 12:52 AM   #1
Justin LE
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The Holy Grail Project

(In reference to this post:
http://www.unicyclist.com/forums/sho...1&postcount=52 )

The discussion of making a Nuvinci work on a unicycle came up several times in the 3-speed sturney-archer build project.

After some mulling around I think I had figured out a way to pull this off and signed up for a frame building workshop last month taught by Paul Brodie in order to learn the techniques necessary for building a custom unicycle frame from scratch.

It's a bit tight for time frame to write much explanation text but I'll post a series of build pictures now that should hopefully be self explanatory!

Starting here is the CAD idea that I had going into the project. The goal was to make a frame that was stiff in the direction of the chainline, since I learned from the 3-speed build that if there is much flex under chain tension, then it makes things more prone to chain skipping problems:
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Old 2012-05-18, 12:58 AM   #2
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Bending Dies

Plywood disks were cut out on a bandsaw to act as a bending die. In the model, most of the bending is with a 100mm radius, and so with the wooden disks cut out at a 90mm radius the metal would spring back to 100mm pretty consistently.
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Old 2012-05-18, 01:02 AM   #3
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Tube Bending

The 1/2" diameter steel tube with 0.049" sidewalls was soft enough that it was easy just to bend it by hand.
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Old 2012-05-18, 01:05 AM   #4
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Bend Check

The curves matched the CAD printout OK, but then moving the bend into the 3rd dimension was going to be tricky. Reference marks helped a lot. The 2nd line here is where the tube needs to twist so that the bending comes out of plane and goes inwards toward the seattube.
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Old 2012-05-18, 01:09 AM   #5
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Tube is clamped flat and then pulled out in 3rd dimension.
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Old 2012-05-18, 01:11 AM   #6
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The same technique was used for both the front and the rear tubes, and then for doing left and right side versions of each. Here are all 4 pieces complete and cut approximately to length.
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