Monday, May 08, 2006

Almost done with Sarah's bike

After dinner, it was time to get back to work on Sarah's bike. It's almost 1AM so I guess I've been at it for a while.

I got the cantilever posts mounted. On the fork, clearance seemed tight even though the crown is fairly wide and the tire is only an inch and a quarter, so I mounted the posts backwards (on the ouside of the fork leg). There's a little more filing and sanding to do, but the post fairs into the fork leg nicely. There's still a small matter of fabricating a new stop for the brake spring on the inside of the post - but that shouldn't take long.

To mount the posts, I used a section of angle steel (normally used to scribe a line down a tube). After fitting the posts for distance from the axle, I measured how far apart they were and drilled corresponding holes in one side of the angle steel. It was necessary to chamfer the outer edge as the post has a radius at its base. Its then possible to slide the posts into the holes, and using the tab with the brake spring holes, clamp the post to the angle steel. The fiddly bit is getting both posts at the right angle to be parallel with the axis of the fork legs or the steatstays (while at the same distance from the wheel axle no less). Unfortunately this jig needs some refinement because it won't stay in place by itself, even though the stays/legs are held horizontally during this operation. Fidgeting with a clamp for a while finally produced enough stability to get a good tack on each post. Once this is done, the clamps can come off and the remaining braze completed for each post. When everthing cools, the jig itself comes right off.

I'm going attach a weight below this jig next time to help hold it in place. Also, I'm going to get some appropriate sized tubing and cut it to length so that I can screw the posts to the jig. The idea is to stick the post through the steel, then slide a sleeve (tube) over the post, then stick a mounting bolt (with a washer) through the tube and screw it into the post. By so doing, the post should be held snug and square in the jig - yet be easier to adjust for its angle. And by eliminating the clamps, the jig won't be top-heavy and inclined to falling off. Well, that's the idea anyway, time will tell if it works. Meanwhile Sarahs posts are in place and look good.

I also mounted the seatstay bridge. Its a plain 3/8 inch tube with decorative reinforcers on each end. After all the difficulty holding the cantilever posts while tacking, this went is very easily - no clamps or nuttin'. It should require minimal cleanup. With the bridge in place, its easier to see that the rear wheel still needs dishing.

So what's left, well the stainless caps have to go onto the seatstays. The pulley mount for the rear brake cable has to be mounted. The brake spring stops have to be installed on the front fork. And theres still a lot of clean up and then polishing the stainless steel. It'll be interesting to see if this gets done before next weekend.


No comments: