Friday, April 21, 2006

Brazing Again

The pins came in plus Freddy threw in some stainless nails for use pinning stainless parts. Cool. Freddy says to file the stainless nails square before use. The first use for them will be to mount the stainless faces on the track fork for Aram's new track bike.

I'll have to post some pictures tomorrow.

One at a time, I pinned the chainstays, pulled out of the jig, and brazed them. The alignment came out perfect. This is my best set of chainstays yet - and I'm psyched because this has always been my problem child. I put Sarah's back wheel in and could even see that it needed dishing (proven by re-installing it backwards).

The bike will use cantilever brakes. A question was whether to put in a second set of seat-stays pointed at the upper down-tube and mount the brakes on these with the brake cable running a straight line up the upper down-tube, or whether to mount the brakes on the normal seat stays and find a way to route the up to the seat cluster and back down to the straddle cable.

I decided on the later course. After studying the McMaster Carr catalog for a while, there were some decent looking nylon sheaves for wire rope (ha ha - the sheave is 3/16" wide - that's some heavy wire rope). I considered putting a pulley near the bottom of the seat-tube and one between the seat-stays, but decided to only use the pulley at the top.

Under the bottom-bracket shell, a bent stainless tube was brazed - sort of like a derailer cable guide. The front end points out parallel with the lower down-tube and the back end points up parallel with the seat-tube. With a little grease, and its large radius, the cable should move through it easily. This means that the front stop for the rear-brake cable will be under the lower down-tube.

For the upper pulley, a cutoff from the small end of a seat-stay will be mitered to fit horizontally near the top of one seat-stay. Before it is mounted, a waterbottle boss will be brazed into the other end. The pulley will need its center hole bored out (but the hub is plenty big for this), and then it will be installed to this hub with a couple of stainless washers and a stainless hex-bolt. It may be necessary to also construct some sort of guard to prevent the wire from coming off the pulley.

Next, a nice Long Shin seatpost binder was mounted. It transitions to a diamond in the front, and has a through-hole in back on the lower skirt. So it looks pretty snappy. It's inside diameter appears to be smaller than that of the tube. I think I'll take care of this when I ream the tube. In any case, even after honing, a 27.2mm seatpost won't begin to slide in.

I finished up the fitting of the chainstay bridge and installed it. I used Freddy's 45 to attach it and then some Brazage filet filler to make a nice radius. Well, 1 & 2/3 ends resulted in a a nice radius. I don't really want to heat the stays again, but I may go back in to finish the one radius. More on this later.

Sarah has now asked for a waterbottle cage. Kind of late in the process. I was afraid it would have to go on the top of the top down-tube - which would defeat the purpose of a mixte frame. Closer inspection suggests that it can fit between the downtubes. The upper hole in the cage may need to be enlarged so that the top of the cage can angle out slightly, but it should fit. Now, the only problem is how to drill out the holes on an assembled frame. Maybe I'll have to rent a drill with a right-angle head.

So, what's left? 1) seat-stays and cantilever bosses; 2) derailer housing stop on the right chain-stay; 3) derailer-cable and brake-cable housing stops at the top of the bottom down-tube; 4) assemble the fork; 5) Pulley mount on seat-stays; 6) Seat stay bridge; 7) clean up (including polishing the head-tube) and ship to painter.

There's enough excess head-tube to make stainless plates at the top of the seat-stays. Do I want to go to that trouble? Hmmmm.... We'll see.

The fork will be relatively simple. I'm using a straight-blade fork crown. So, its almost time to dig out the fork jig. Naturally, the fork will also need cantilever stops mounted. To those ends, I enviously eye the Henry James brake and bridge jig. I'm going to need a bit to think up my low cost alternative. More on that later.

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