It’s day two working on the fillet road bike for the 2011 NAHBS and it’s going very well. Where yesterday was working with a few large tubes today was all about the fussier and smaller stuff used in the rear end of the bike. Or as my old partner in the lug shop at Serotta “Chief” used to say – “it’s time to add the ass end to this thing.” For what it’s worth, this is my favorite part of framebuilding. In my mind it goes from not being a bike to being one. I like that.

The first thing I need to do to add the ass end is to assemble the chainstays. This involves brazing the Triple F dropouts into the c-stays, doing the clean up work to those joints, mitering the c-stays to length and finally putting the small clearance dents into the stays to make sure we have enough room for a real tire and chainrings.

Brazing the dropout to the c-stays is done using brazing rings. I make these rings by wrapping brazing rod around a dowel of the proper size. The c-stays are prepared by cleaning them out on the inside and using a deburring tool to give the inside edge of the stay a slight chamfer. I then press the rings into the c-stays and they are held in by the spring tension. This set up allows me to invert the whole shooting match, heat the dropout ball and then flow the ring inside the c-stay. This makes for an extremely strong and simple joint with very little heat. Once the inner ring is flowed I add a small external fillet to blend the whole deal together and it’s done. And like the joints on the front end of the bike they are allowed to cool before soaking the flux off and doing the finishing and polishing. The lower end of the seat stays will be brazed to the dropouts in the same exact way when the time comes.

With the dropouts and stays happily married it’s time to cut the c-stays to length and miter them to fit the BB shell. I set these up in the jig with just a dummy BB shell to make it easier to see what is going on. After the c-stays are mitered it’s time to give them some shallow dents for clearance. These dents allow for fairly short c-stays while still having room for a 27 mm tire.

Then it’s time to clean them inside and out in preparation for being brazed to the BB shell. The cleaned and fluxed parts are assembled in the jig and then same tinning process that was used up front is done here.

Now I need to close the triangle by adding the seat stays. The lower ends are prepped just like the c-stays were and the upper ends are done mitered by hand to fit to the pinch barrel I brazed onto the seat tube yesterday. You may notice that I miter the s-stays so they hang off the back of the pinch barrel just a bit. It makes for a cool looking edge left there but that is not why I do it. It’s done because it makes for a nice acute angle inside the upper s-stay where is meets the pinch barrel which makes it easy to flow lots of brass inside to make a super strong, lifetime joint. I in effect fill the upper 2 mm or so of the s-stay with brass and it makes for a solid plug where is meets the barrel.

This all sounds easy as I type it out but it is very fussy to do. The stays need to be the same exact length as one another and have a perfect fit between the dropouts at one end and the barrel at the other. One file stroke too many and the tube is too short – not good I must say. Couple that with the fact that it’s a compound, offset miter and I can say it’s a challenge. Once to the right length I shape up the little points on top and clean up both ends and they are ready to braze in place.

Next up is cleaning and brazing/tacking the s-stays in place. I tack the upper end of the s-stay to the barrel with a small amount of braze just to hold it in place but I braze the lower ends to the dropouts completely.

Once this is cool the bike gets pulled from the jig for the last time. I do a quick check of the alignment and then fit the ‘brake bridge T’ to the frame. It is a T shaped tool that holds the rear dropouts at the right spacing and it has a hole at the end that will locate the brake bridge. With the T in place I miter the brake bridge to fit and do the whole cleaning/fluxing/brazing deal you’ve seen on the other joints. Having the brake bridge brazed in before moving on is super important. The brake bridge closes the triangle formed by the s-stays and makes the whole thing stable and rigid so I’m sure things won’t move around when I go to braze the upper end of the s-stays to the barrel.

Lastly for today – I flux up the rest of the ass end and lay the rest of the fillets. These fillets, at the BB and pinch barrel, are tougher to do with the limited space I have to work in. Not so much hard as fussy. Combine this with the fact that the flame from the torch will sometimes get caught in a cupped blob of flux, like when you rinse a spoon in the sink, and turn around and come back at you to try to burn your hair off and it can be interesting.

Tomorrow I soak off the flux, do some finish work and machining and add some more stuff to it and we should be close to having the frame ready for paint.

More then.

Dave

This entry was posted on Thursday, January 27th, 2011 at 8:15 am and is filed under Uncategorized. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.