Friday, April 27, 2007

Menial labor

I spent the last 4 hours prepping and packing up the Twinsix 29ers - I guess you don't realize how boring a job like that is when you usually just do one frame at a time. Man, I'm sick of using the bottom bracket taps...

In other news, I've done a little bit more work on the downhill bike. Progress since the last update includes:
-Ordered an el-cheapo front 20mm hub, and matching 36 hole 700c Rhynolite rims. I ended up selling my DT Swiss 165mm hub on Ebay (and only got a lousy $30!) because the 165mm standard seems to be disappearing, and in looking at the hub (which I got for free, so whatever) I noticed that the flanges aren't actually any farther apart/wider than those on a 150mm hub - the ISO disc mount is just extended way over to the nondrive side to make it line up right. Lame. So in any case, I got a no-name rear 150x12mm hub from BTI (it weighs an astounding 800 grams with the axle!) which will let me build the frame around something a little more normal. Some of you are probably wondering why I didn't get a set of Kris Holm rims for this beast - and essentially, it's because I'm light (150 pounds) and the Rhynolites are dirt cheap (<$20 each). If I blow them up, I won't complain.

-Built the start of the swingarm (see pic on the left). The sleeves are 1.125"x.095" machined to fit a 24mm axle, the arms themselves are 1.5"x.75"x.049" 4130 (probably massive overkill), and the pinch bolts are standard jobbies from Nova that are intended to be used on a seat tube to hold the seatpost in place. The sleeves are fillet brazed onto the arms because TIG welding this would cause some distortion problems that would probably make the sleeve no longer fit the axle without further (annoying and difficult) machining. Doing it with brass is plenty strong and saves me from having to deal with that problem.

-Built some nice ghetto dropouts. These are made from 1/4" 4130 plate and some cheapo 3/4" angle. Yes, I could have just gotten a set of Instigator dropouts and machined out the slots to 12mm, but this was, theoretically, more fun (and given that it only took 15 minutes, and the Instigator dropouts are $50 or so, it was the cheap option). I still need to do some finishing work on these and bevel edges and such. I didn't do the pinch bolt thing here because the 12mm axle uses HUGE hex nuts to bolt on and I think it'll be plenty stiff as it is with vertical drops.

Still to do:
-Gotta order more 1.5x.75 for the rest of the swingarm - I realized that I was like 6" short of what I need. The rear end of this frame is going to be ridiculously overbuilt - if I used 1.25"x.625"x.035" rectangular tube for the swingarm, I think I'd save like a pound and a half. But given that the frame is modular, I can always go back and build a second (lighter) rear end if I want to try it. Sarah's DH rig uses the .035" rectangular stock for the rear end and has had no problems in a couple years of hard riding, so I'm probably being overly conservative here, but I want to be able to lend this bike out to friends (some of whom have 80 pounds on me) so I figure it can't hurt. Plus I'm not about to start racing DH again, so a heavy bike doesn't really bother me.
-Build some wheels. I can steal Sarah's front wheel if needed (if I get lazy), so that won't take long.
-Install shock mounts and hardware. This shouldn't take long either. I'll probably put a long shock mount with a whole row of mounting points on the downtube so that I can play around with rising/falling spring rates and/or use a different eye to eye length if needed.
-Powdercoat. I'll probably ride it first to see how it works. I promise this one will get powdercoated before the start of the summer, though!

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