Tuesday, May 19, 2009

Big in Japan: Epic Finale Post

Well, ok, if by "epic" you mean, "regarding the installation of the seatstays and some small braces".

Seatstays. Argh. Every framebuilder's least favorite part - they require bending, multiple funny-angled miters (one of which is 90 degrees out of phase with the other), and they're structurally just about the least important part of the bike. I mean, you need them there, but they can be asymmetrical, mismatched, made from cheap carbon fiber, bolted on with chainring bolts, etc, and nobody would ever be able to tell while riding.

But everyone can see them. People who wouldn't bat an eye at a horribly mangled set of chainstays, or massive dents in your downtube, or missing paint, will make their opinion regarding the shape of your seatstays known every time. Many folks seem to think they're the end-all and be-all of creativity when it comes to frame design, and some people even think putting funny bends in them will make for a smoother ride (let out 5 pounds of tire pressure if you want that, folks).

So needless to say, on some days, seatstays are the bane of my existence. Today was one of them. I bent and mitered up a set of the super-burly 20mm (and .9mm thick!) seatstays I got from Burly when they stopped making bikes a few years ago. These stays are strong enough to probably use as *chainstays* for a relatively small person on a road or 'cross bike (I might even build one for some tiny person with them someday) and they're also great for 220+ pound folks. Yes, I could make custom stays from 3/4" 4130 or something, but for the price (I believe they were about $1 each, Burly was never going to use them again) these are a great way to do things. They also have a taper and built-in "bullet" at the dropout end, which is totally kickass.

Anyway, I bent them, and I mitered them, and then I mitered (slotted) the dropout end and went way overboard. The slots were WAY too long and the stays sat like an inch below where I wanted them on the seat tube. Just a brainfart, really, but super frustrating. Luckily I still had the seatstay fixture set up, so I tossed the stays into the "Misc stays" box (yes, it's got a LOT of random stuff in it!) and re-did the whole process. Bummer. One of the lessons I've started to learn (but still struggle with) is knowing when to give up on a part, toss it in the recycle (or re-use) bin and start over fresh. Sometimes it helps to go for a ride or take the dogs for a run before re-starting, too. Or smash my head into the wall a few times. In this case, it was too early for either, and I was still in a pretty good mood, so I just redid it.

And they came out just fine the second time around. As you can see, there's actually not that much clearance for a disc caliper (remember, this is a 21.5" frame, so the seatstay isn't as close to the caliper as it would be on a more "normal" sized frame). The BB7 is one of the biggest calipers on the market, so I figured that was a good one to test it out with. For smaller frames, I'll have to do a second seatstay bend at the dropout end to keep the stay up and out of the way. That's assuming, of course, that more folks want to use these dropouts. So far, I'm a fan.

I also have run out of low-fuming bronze (the stuff you use for fillet brazing, and which I usually use for braces and bridges because it's less work than using the TIG welder) so I had to TIG the seatstay bridge. Here's a quick shot of that.

Final frame brazeons (I need to decide how to route the rear brake line!) will be done tomorrow, but here's a shot of the 95% finished frame. She's a beast - about 6.5 pounds (and I haven't added the cable stops and rack mounts yet). But given that my own frame is something like 4 pounds, and I weigh 150, I think Derek is actually doing pretty well there.


Jon said...

The dropout area looks pretty nice.

Is the seatstay bridge a tube (instead of some of your other widgets, like the old disc rotor) because the bike is for a heavier rider or heavier duty? Anything else that drives that choice, like terrain or intended use? And while I'm at it, when's the bridge completely omittable?

Walt said...

Jon -

In this case, Derek needs fender mounts (water bottle bosses brazed into the bridges) so I used tubing. I've never figured out a great way to make a plate/disc rotor seatstay bridge and attach a fender mount in an attractive/functional way.

You can (and I have on my own bikes) leave the bridges off entirely and I don't find that there's much of an effect. The seatstay bridges have traditionally been for mounting brakes (on road bikes) or fenders, or for making the rear end a bit stiffer when using v-brakes or cantis.

There's great debate about chainstay bridges among framebuilders - some swear by them, and say that the bike is noticeably stiff with them, others (like me) say they were originally for mounting kickstands and serve no purpose.


steve garro said...

always start seatstays 1st thing in the morning when you really feel it.......my re-cycle bin record is 3 sets before i got the right ones, on an 11" frame. i was about to crack! rock on, Steve.

Sabrosa Cycles said...

Amen Brother - I usually place my recycle bin on the other side of the shop so I can at least throw the seat stays towards a receptacle of some sort instead of a wall. I’m with Steve. Seat stays usually go better for me first thing in the morning.