March 25, 2013

It Almost Looks Like A Bicycle

I made the seatstays using pretty much the same process as I did for the chainstays, but with carbon fiber cloth instead of bundles of tow.  I plan on adding an aluminum insert for the rear brake to clamp into.

 Rather than using a bunch of layers of cloth, I decided to try embedding some thin pre-made carbon fiber tubes into the seatstays, and only using two layers of cloth:

With the frame tacked together, I started making the lugs to reinforce the joints.  I found that the only way I could get a decent seal in the vacuum bag was to enclose the entire frame.  If I tried to pull a vacuum locally, the leak rate was too high to properly compress the joint.

This is what the reinforced head tube joint looks like after some sanding:

I did some work around the dropouts as well:

In an effort to make my vacuum bagging technique slightly more legitimate, I used peel ply and some resin-absorbing cloth around the seat cluster.  Unfortunately, this joint had pretty severe seams around the edges, but I don't know whether they are due to the the cloth or the mediocre vacuum I was able to get.

This being a zero-dollar project, I was concerned about how I was going to get a carbon fiber fork.  Molding one myself would have been very difficult, as the fork needs to interface with bearings and a stem, meaning it has to be more precise than I could manage with a foam mold.  My leading idea was to find a large plastic billet, CNC out a female two-part mold for the fork at Edgerton, and positive pressure molding it, like how real bike parts are made.

Out of curiosity, I sent out a query to reuse-ask, to see if anyone on campus had a working or only slightly broken carbon fiber fork they would be willing to part with.  I thought it was a bit of a stretch, but I got a response within four hours, from someone with a fork that had been crashed.

I sanded the area down to get a better picture of the damage.  With the paint removed, it actually didn't look quite as bad.  I sanded out all the cracks, which did not actually go all the way through the tube.

I applied a four-layer patch to the damaged area, starting with a small patch right over it.  Each additional layer was larger than the previous one, so that the patch gradually increased in thickness from the undamaged to damaged area.

I sanded down the patch, and stripped the rest of the paint off the fork.  I still haven't decided how to finish the surface yet.

With any luck, the frame should be finished within the week.  In terms of components, I have everything except for a chainring, a front tire, a headset, and a stem, so I should be able to build up the bike shortly after finishing it.

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