Wednesday, June 08, 2005

Beginning to Look Like a Frame

Well, Renaissance (aka Banana Brain on eBay) contacted me to say that they were on vacation in Norway. Anyhow, they're going to look into my missing BB taps when they get home. I hope so, I could use them right about now.

Meanwhile, I installed the seat-tube last night. I use 4 v-blocks: 2 supporting the headtube, 1 under the downtube near the BB, and 1 under the top end of the un-cut seat-tube. To compensate for the reduced diameter of the seat-tube, a 0.06 inch shim is placed under it's v-block.

The seat-tube was angled at about 72 degrees (back from where my drawing had it at 74 degrees). So, I put a bar in the spigot and set the BB and headtube on the ground. A good push resulted in a looser joint and the ability to tip the seat-tube farther forward. Still, I needed to give the inner spigot a touch with the die-grinder before the tube would stay in the 74 degree position. I then tightened up the joint with a drift and a small ball-peen hammer.

Once again, the joint was set using pins. With a fear of having anything shift out of alignment, it was time for a belts and braces approach. I mounted an extruded beam across the head-tube, down-tube, and seat-tube - with the 0.06 shim between it and the seat-tube. All looked good as this structure was mounted in the stand for brazing.

But, alas, this proved to be a bad approach. Because of the jigging, it was hard to reach the far side of the BB with the frame. This led to two problems: 1) the joint didn't finish as cleanly as the others; 2) the heating of the seat-tube was uneven from side to side.

In the first case, I've already got a couple of hours into cleaning up the shoreline. It'll probably take a couple more. Doing this for myself, I have a new appreciation for the filing skills of the pros - even if they don't have to use them to clean up sloppy brazing.

In the second case, I set the cooled frame on my table and found a significant mismatch between the alignment of the head-tube and seat-tube. After lots of fumbling around, I decided to test the head-tube/down-tube/BB by holding the tubes to their v-blocks and checking the squareness of the BB against the table. This looked good, which was encouraging.

After mounting the BB in the vise between 2 pieces of 1/2 inch ply, I gave the seat-tube a tug. The workbench (weighted down as it is) and the ply were no match for the tube. It was time for plan B. I have a section of thick (probably 3/8 inch wall) 4130 tubing about 4 feet long. It's a little smaller in diameter than the inside of the BB. With the tube pushed through the BB and both set on the floor, I proceeded to step on the tube while pulling on the end of the seat-tube.

I could feel movement - yea! But, when the frame when on the table, it was now out of alignment in the reverse direction. Was this going to be one of those endless back and forth affairs? Well, I put the frame on the tube the other way around and gave a gentle tug. Back on the table, everything was now aligned, and was as perfect a match to the drawing as I can measure. Despite the ugly joint, I was quite pleased with my efforts.

Speaking of the ugly joint, I had one drip of filler that ran down the grove between the DT, ST, and BB barrel. It looks like death to file out without messing up the BB shell itself and, tada, the edges of the drip can't be felt with finger tips. It's a very thin drip with a nicely feathered edge. So, this is one I won't even touch.

On the other hand, on the side of the ST spigot, the shoreline forms a shallow half-moon. This got largely obliterated. It was so bad I took a carbide bit in the die grinder and went at it. This roughed in the shape pretty well without mishaps, but now there is still lots of hand sanding ahead.

Tonight won't be a building night. There is too much work to do for a number of other projects. But, hopefully, tomorrow will be the installation of the top-tube. With that, I'll have a front triangle.

Meanwhile, my build-kit has arrived from Yellow Jersey (Madison, Wi). It's basically a Campy Centaur build with a compact (FSA alloy) crank and a sprung Brooks Pro (aka Conquest) seat. I've decided to hold off on the flat bar for now - but will experiment on it with my next bike. The wheels are built with Velocity Aerohead rims using the asymmetrical rear rim. The rims are electric blue. I'm sure the blue rims and sprung Brooks seat sound like a strange combo. Hopefully, the final paint will pull the image together.

That's all for now folks.

No comments: