Monday, January 09, 2006

Busy Hands

Hello again,

I'm beat, but that's not all bad. Work is busy, so I'm making some money. And my second league of curling started with a win. But, the key thing is that I built a carbon bike this weekend.

I started with a Black-Pearl front-end and a Black-Box/Drive-Tail rear-end. This will be assembled with a Black-Drive fork. This is all top of the line Dedacciai carbon.

The first step was to mount the frame in the jig by the BB and top of seat tube so that the seat tube angle could be set correctly. Then, it was time to chose chainstay length. I went a little long for a more stable ride. Because the extra length comes from the monostay at the front, it shouldn't create too much flex. Then the bottom bracket drop was set with the dropout mount.

With this accomplished, the monostay and its socket (along with the stay ends and the dropouts) were preped by sanding well and then cleaning with a rag and acetone. The later was accompanied by gloves and a respirator. The 3M epoxy is an aerospace grade two part in black (to match the carbon).

The epoxy comes in cartridges with dual cylinders. This mounts to the front of a little handle which operates much like a caulking gun (but is much more precise - in fact its manufactured in Switzerland). A long mixing tube attaches to the front of the cartridge and can be replaced with a cap to save the remaining epoxy for later use.

The epoxy is a bit more liquid than I expected. This has two immediate consequences: a) it flows more easily through the baffles of the mixing tube than expected; b) it drips more easily than expected when applied to frame parts. The former is great and the later is manageable - so far so good.

Epoxy went on the socket and the monostay, they were pushed together, then the same with the dropouts and the dropouts were locked into the jig. Finally the acetone rag was used to clean off the excess epoxy. Well, that was easy. To facilitate curing, I positioned my portable heater under the frame (but not while the acetone was nearby).

Next comes the seatstays (also a monostay design). A post sticks out of the seattube, pointing toward the dropouts. It has a slight taper so that it is narrower at the lower end. The monostay is much bigger around with a triangular cross-section. A carbon fiber moulding that is triangular in shape with a small hole bored through the length fills the space between the the two.

Its necessary to sand down this filler to fit into the monostay and leave space for epoxy. I also mitered the one end to approximately fit the seattube. This was then epoxied to the monostay with the miter sticking out of the end. Next the dropout fittings were epoxied to the ends of the seat stays. These were loosely fitted to the dropouts and the top of the stays propped against the seattube until the epoxy was essentially cured.

Then the seatstays were unscrewed from the dropouts and I began the process of mitering the monostay to the seattube. For this, a 6" cutoff wheel was mounted in the drill press. First the tube was cutoff at the same angle as the filler (by eyeball). Then, using the side of the wheel, the miter was ground off a little at a time and carefully checked for fit in length and miter. After a patient process, a good fit was obtained. Then, the stay was popped into place.

This is a little tricky. The dropout fittings fit into a sort of a pocket in the dropouts. The best approach for sliding the monostay onto the tube on the seattube was with the stay ends below the dropouts. When it gets to the point where its necessary to slide the fittings up against the dropout, a little edge is in the way, and I had to slightly pull the stay ends apart to fit. Knowing the rigidity (and potential brittleness of carbon), this was a nervous time. But, it actually proved to be a quick easy process as everything popped into place.

Then having proved the fit, I had to pull this apart again, apply epoxy to the monostay, seattube, and support tube and put it back together again. Again, this proved easier to do than describe. Some more wipe up with the acetone rag (being careful not to pull epoxy from the joint) and I could screw the fittings into the dropouts. Actually, I put some medium thread-locker on the screws. Then the heater went under the frame again and I sat back to look at what I had. It looked nice.

After things had cured for a couple of hours, it was time to tackle the waterbottle mounts. Now there were only two problems with this plan: a) I'd never used this blind mounts before; b) it wasn't clear if the frame was designed to have them placed in any one position. After a talk with Joe, it was clear that I could mount them according to functionality and not the design of the carbon tubes.

So, I got out one of the mounts, put it into the tool (which came without directions) and did a practice application in thin air. Basically, this works much like a pop-rivet. The tool has a pair of levers which are squeezed like a pliers. On its head, there is a mandrel on one side. Sticking out through this is a narrow treaded rod.

The mount is screwed onto the rod. When the levers are squeezed, the rod pulls the mount toward the mandrel, and the back of the mount's tube crushes outwards. When pulled far enough, this crushed tube presses up against the back of the frame tube locking the mount into place. Hope that's clear.

So, I marked and drilled holes in the seat tube, applied epoxy to the holes, and had at it. The epoxy was to help prevent the mounts from rattling and to prevent the carbon fibers from contacting the mount. I chose stainless steel mounts, and hope that this combined with the epoxy insulation will ensure against any galvanic reaction between the mount and tube.

I also squeezed the handles slowly and carefully. My goal was to just set the mount firmly without crushing the frame tube. The carbon is least strong against compression, and I don't want to crush this expen$ive $tuff. Anyhow, this appears to have been successful. There is no sign of looseness even with the a bottle cage mounted. There is no evidence that the tubes were crushed at all (I could feel when the mount was just drawn up against he tube - and stopped there, no cracks [even tiny hairlines] showed in close inspection of the epoxy near the mount, & no surface deformation was detected when tested with angles of reflection). Based on this, another mount was placed on the down tube with similar results.

The Black Pearl comes with with a front derailer clamp and specific torque instructions. So, the Campy derailer (w/35m clamp), that I planned to use, is a no go. I got an FSA compact instead. From a little way off it looks like a Chorus compact, its at least as light (published weight), and it doesn't cost much.

I mounted this and a purple anodized water bottle cage and showed the results to my wife (who doesn't impress easily when it comes to bikes). Her reaction was "Sexy Bike! But you've got to get rid of the purple cage." OK, everyone has different tastes, but the frame looks great. I took it with to spinning class and may have garnered two buyers (even without decals or clearcoat). So things are on track.

The cable stops still need to be mounted (I should have the right rivets by tomorrow), and I need to find a nearby painter. Then it'll be time to build and show it to the world.

Meanwhile, I've begun to cut tubes for a new steel frame for me. I'm trying a combo of Versus and Versus HT (depending on availability for desired sizes). This will use HJ mountain bike lugs for the top Head Tube and the seat cluster. The lower Head Tube and the BB will be Walter, resulting in a sloping top-tube 700c wheel design. The dropouts are forged steel with stainless steel fork tips and an HJ fork crown. The crown has 3 degrees of rake built in, limiting but not eliminating the bend in the fork legs. Everything is being built to accommodate fairly wide tires (I'll probably start with some 32's), and of course fenders.

The top and seat tube are mitered as is on seat stay. The downtube needs to be done, the seat tube needs to be cut to length (the seat lug caps the tube so that there is no extension), and the stays finished. Then its pin and braze. I'm looking forward to that.

More soon - but as I said, I've been busy.

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