Wednesday, August 29, 2007


Should posted this before the last posting - but I forgot to upload it.

What’s new?

I’m recently back from a family trip to the Eastern Sierras around Mammoth Lakes, CA. It’s a lovely part of the country and a great place to visit. With my lungs, however, I could never live there. We took 5 days to acclimate to the base altitude (8000’). This got me to the point of being comfortable, as long as there were no stairs to be seen. Then we packed in to camp for a few nights at 11,500’. We were on the shore of a beautiful blue lake rimmed with mountains – the sights couldn’t be beat. But, walking up from the lake to our camp (maybe 25’ of elevation) was enough to wind me. Ugh.

Many projects have been on hold for a while, but I’m beginning to finish them. The path racer is ready for paint except for some final filing around the track forks (dropouts). I’m pleased with how it looks, and it should be in the painter’s hands within a week. Janet’s randonneur frame is done and will go to paint at the same time. Charlie’s carbon frame is designed now. See picture below. It will be carbon (from an old trek 2500) w/ a steel bottom bracket shell, chainstays, dropouts and front fork. Charlie wants Gordon to paint this to look like my bike – which sounds like fun to me.

On Charlie’s bike, the BB will be lugged so that the down and seat tubes can be bonded in. This will involve filet brazing and I’ll try to get some pictures posted of the process. The head tube and seat cluster will be wet wrapped carbon that is vacuum-bagged to pull out excess epoxy. The seat cluster will be complicated because I’m using traditional stays (carbon of course) on either side of the seat tube. So four tubes come together in one place and need to be wet wrapped, then wrapped with a material through which the epoxy can pass, but which will not stick to the finished work. All of this then gets wrapped in a bleeder felt which allows air to be pulled out by the vacuum pump and which sucks up and holds the excess epoxy. Then, a plastic ‘bag” has to be put around all of this and sealed up (especially where the tubes pass through) so that the bleeder felt can do its job while the epoxy cures.

For the initial connection of the stays to the seat tube, I’ll be using my old reliable Scotchweld 420. This sets up in about 20 minutes, and should hold things together through the process of wrapping the joint up. A balsa plug will be located in the rear of the top tube so that the top tube can be similarly affixed to the seat tube before wrapping and bonding. All in all, I expect this process to take about an hour from first gluing until the bag is being vacuumed. This setup will be left to cure for 36 hours, then the vacuum is shut off, the bag removed, and the felt and transmission layer peeled off. Using a Mylar transmission layer (generally with perforations) can yield a very nice smooth looking outer surface. Given the complexity of the seat cluster, I’m not planning to use Mylar. Instead a specially treated polyester cloth (woven) will better follow the contours of the tubes. Even then, I expect to see some ridges, creases, and thick spots in the epoxy. My goal will be to sand these down to something presentable before shipping the frame off for paint.

Assuming that Charlie’s bike goes well, I’ll build a full scale prototype for me to ride. This will continue to use steel chain stays as an economy move. I have plenty of experience bonding carbon rear triangles – so I’m not worried about how that works. With two finished bikes in the bag with lugged bottom brackets and vacuum bagged head tubes/seat clusters, it should be time to apply this method to a production bike. I may apply this to Tim’s prize bike. It is a small frame size – which presents a builder with certain challenges in both design and construction. This system takes me away from the constraints of pre-built lugs which will make Tim’s bike easier to get right.

With Tim’s bike, we may also go with an aluminum bottom bracket. Bottom brackets are made in both aluminum and steel with a lug for bonding in a carbon seat stay. This would require outsourcing the TIG work of putting lugs socket son the bottom bracket for the seat and down tubes, but should reduce the overall frame weight. Similarly, I may look at milling grooves in the aluminum head tube. Because it will be carbon wrapped, it may be possible to take a little weight off of the aluminum. And, when we’re all done, Tim’s going to have a great frame!

I’ve also nearly finished a fork for an old project bike. Actually, the fork could go to paint right now. But it has a stainless crown and tips – and polishing takes a long time. I was pleased to find out that other builders have the same challenge as me. This is, to see a remaining scratch from one level of grit (be it sand paper or buffing compound) requires polishing down a couple of more levels. So it’s a two step forward and one step back kind of process. I find that it’s important to be in the right frame of mind.

When working the stainless, pressure has an equal impact to grit. It’s possible to work a piece for a while, and with one stroke of two much pressure, scratch a layer that needs to be sanded out before proceeding down the levels of grit. This plays out especially with oddly shaped pieces (can you say lugs, crowns, and dropouts?) where an even pressure needs to be applied around varying contours. On a nice flat surface, I can work through a series of grits with a flap wheel sander and have few problems. The flap wheel sander works fast, which is nice. But through in a corner or a curve and it may be possible to sand through the piece before getting it uniformly ready to work down to the next level of grit.

So, I’m about halfway, maybe a little more, through polishing this fork. But it takes a peaceful/patient frame of mind to get through this work. With what’s in front of me, the fork is being set to the side until I catch up a little. Anyway, when it’s done, another frame will go to the painter.

Finally, I’ve been filing (on my trip) some old Cinelli pressed lugs and have them almost ready to go. This is for a track frame I’m building for my neighbor. He want’s something very traditional. He’s got a Record Pista crankset, some nice pedals, a Cinelli steel stem (and soon a matching bar). He’s working on building up a set of wheels with some Record Pista high-flange hubs and some nice old Campy rims.

The Cinelli lugs are more symmetrical than some of the pressed lugs that I’ve used. But, in the weld area, near the edges, there is some porosity. We’re going with a cast Cinelli bottom bracket which should arrive this week. Hopefully it’s in a little better shape.

For tubing, I’ve been considering lots of options. The rider prefers to stick with Columbus – which is fine with me. However, there is a limited variety of standard-sized tubing available in the newer metals and these tend to have thin walls. As a consequence we’ll probably use one of the old sets of SL that I have kicking around. While I grew up thinking that SL was dangerously thin and whippy, it’s seriously a heavy gauge tube compared to modern tubing. If an SP downtube can be found, that will probably get subbed in. Also, we’ll look at the option of going to a heavier gauge chainstay. Together, this should provide the rider with the stiffness he desires while sticking to traditional tubing diameters.

My plate is full, eh? Also, I need to do some reconfiguration of the shop to make my space more efficient, and I’m starting to look at lathes. There’s lots to do so I’ll stop writing for now and get back to work. See you soon.

No comments: