July 13

July 13, 2005

Disc wheel covers

The rear wheel not only spins inside an envelope, but it spins without spokes to churn the air up. I am using a Zipp 404 700 wheel and used the blow molding method to make a PETG mold. Then I made two light carbon fiber wheel covers. The wheel is held in place with simple double sided tape which seems to work just fine. I'll probably find some kind of light contact cement to provide a better seal. Currently, the hole in the center of the disc rubs on the side of the hub while turning. I will probably expand that hole slightly so that it doesn't touch the hub.

Here are the details:

1. The PETG sheet is clamped in and the table is spun around while the infrared heat lamp melts the plastic.

Ben is centering the table on the spin axis.

2. The 'x' marks on the PETG are so I can see how far the plastic has sagged as it is heated up. Without any marks on the clear plastic, it's impossible to actually see what it's doing during the molding process.

Then it's screwed down to a plywood base, and filled with expanding foam from a hole in the back of the base. The hole is then plugged with a cork.

3. On the first disc, I put a single layer of 5.8 oz. cloth on, but I think it's a bit too thin. So I added two layers on the second disc. The first disc is OK to use, but the vacuum sucked all of the epoxy out between the woven fibers and air leaks through now. I'll have to coat it with a thin layer of epoxy to make it relatively air tight.

This photo shows the disc from the back side. The PETG mold makes for a PERFECT epoxy mold, as the epoxy won't stick to it, and it leaves a super fine and glossy finish. Too bad this isn't the FRONT of the disc.

4. This is the disc from the front showing the texture of the peel ply. It would be glossy and smooth if I painted on a thin layer of epoxy, but I want it to be light, so I'll probably skip the bling treatment.
5. Both discs on the 700 cc Zipp 404 wheel. I tried to put this on the front fork of my road bike, but the discs are too wide and they rubbed on the forks.


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