Bending Lower Rails for a
Wide Tyre HD Frame III

Right, now we've arrived at the gnarly bit, essentially it's a repeat of what we did on the last bend. The gnarliness is due to the awkwardness of the bend and the fact that there isn't enough straight tube after the kick out to get it in the bender, at least not on mine. This is fairly easily solved by back bending, which is the technical term for putting the bend line after the bend and bending it from the opposite end of the rail. Fig.10 shows the angle finder and the test bend being used to establish the angle of the bend. The test bend is positioned so that it lies over the line drawn on the board foe the rear kick up and its bend is tangential to the rail. The angle finder is then set so that it is parallel to the rail on one leg and parallel to the mocked up kick up on it's other leg, which gives us the angle for the bend.

Fig.10

The rotation required is then measured off of the angle finder in much the same way as we measured the rotation of the down tubes to do the previous bend. Since it has flat surfaces though we can dispense with the steel plate.

Fig.11

Fig.10 makes it fairly obvious that for this bend, if it was bent the same way as the others the bend line would need to be somewhere in the kick out bend. Short of sawing lumps off of the former to clear the bend (which isn't an approach I favour) the only option is to bend it from the other side of the bend which gives us a bit of a problem in locating the bend line. But if you think back to Fig.2 you might start to see how it is done, to save you backing up to Page 1 here's the pic again.

Fig.12

The mark on the test bend (which we had to clean up and remark for the photo) that is at the point where its tangential to the rail is the 7" mark from the bend line. So we transfer that point to the rail and then measure 7" to the rear to establish the bend line we want. So now we have the three pieces of information to make the bend, due to the sheer awkwardness of this and the large amount of eyeing things up there is a good chance that the measurements will be off. It would be better to spend more time on it than we did and tack up some props to hold things in place as this is going to improve your chances of getting it right. Another thing that'll improve your chances of getting it right is a wire model of the rail. I'd forgotten about these until Weyland Smith mentioned it on Chopper Web but they're dead handy for strange rotations

Fig.13

At this point the rail goes in the bender and the wire model is use to approximate the rotation, which is then fine tuned using the steel plate and angle bubble. The angle finder is positioned to let us gauge the bend and the thing is bent. If it's slightly out don't worry about it get on and bend the other rail using the same process. As you might have guessed by now we deliberately screwed our rails up so we could show you how to fix it (Ahem-mm!).

Fig.14

As you can see from Fig.14 all our errors crept in the same direction so the ends of the rails converged. But no biggie, we'd cut the rails to 108" so there was plenty of meat on the end to give good leverage for some correction. you can also see that the bend line is the other side of the bend for the kick up when compared to all the other bends.

Fig.15

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