Thursday, January 26, 2006

Some Pictures Finally

Well, here are some pictures of my latest frame project (010106). It's a sloping top tube road bike. The upper lugs are Henry James mountain bike lugs to get the slope. The bottom are Walter which give me the BB drop I want with 700C wheels. Also, the lower head lug has built-in ergo stops. Very cool.

I've been fiddling with joint fit and geometry. This is much easier with a jig than off drawings IMHO. Borrowing an idea from Nic Crumpton, I've clamped a piece of 1x1 angle channel to the the bottom rod that carries the head-tube cones. This gives a reference point for where the steering axis touches the ground. Thus its possible to ensure that the bottom head-lug is positioned properly for the chosen length of fork. Very nice.

Things were looking good tonight, so I took to filing down the seat-lug. It needed a lot of work because I didn't like parts of its shape. The seat-tube ends within the lug. There is a ring around the top of the seat-tube spigot, so its important to get one's seat-tube length right (see prior paragraph) as there's no leaving it to long and trimming later. Because of this design, the lug essentially has a flat top. There's probably a good engineering reason for this relative to mountain bikes, anyway I picked the lug so I'm not complaining. But, the transition from the sides of the lug to the top was a bit to amorphous for me. In fact the whole seat-tube barrel and the lugs for the binder bolt also seemed from a visual perspective to be a bit too much like pudding.

So, I spent a couple of hours with a file, and got a result that looked much better - especially when mounted on the tubes. Anyhow, everything was fitting fine, and I've had an itch to get the torch back in my hand, so I had a go at it.

First the usual cleaning of lug and tubes. Then drilling and fluxing. Finally pinning the joint and checking everything in the jig. Looking good, so on to some more flux, mount the joint in a work stand and have at it with the torch.

The pictures were taken after the finished assembly was put back into the jig to check fit. The jig isn't an alignment table, but things looked real good.

For having been away from the torch for a while, I was very pleased with the braze. There was a little bit of cooked flux on the crotch of the joint, but overall things looked good. The edges were clean and require no filing. Not to much silver was dripped in the wrong places. The edges are nice filled showing that I pulled the silver through well. There's a nice ring of silver at the end of the seat-tube inside of the lug. Cool.

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