Friday, 12 June 2009

Finishing the plug

Today the first part of the frame has been laminated. But as I am a little bit behind with the blog I will start out with some previous work.

The plug now consists of all the major components. To finish the plug first I have to add a metal plate that will function as a connection plate for the chain tensioner. The chain tensioner will keep the forward chain tensioned and will allow the front cranks to be moved forward or backward without changing the length of the chain.
The picture below shows the recess for this plate. On the right you also can see the place where the foam meets the intermediate tube, this gap will get a fillet.

At the positions where the front seat will be mounted a fillet of thickened epoxy is applied into a recess. To mount the seat I will drill a hole in the finished frame.

All epoxy is mixed with cotton and glass spheres. The cotton gives strength, and the glass spheres make the mixture thixotropic and easy to handle.
as already mentioned, the gap at the connection between all metal parts and the foam is filled with the mixture to make a nice and even plug.
The area around the bottom bracket gets extra attention to achieve nice fluent lines in the plug.
After application of the mixture the surface still looks rough and uneven.

The surface of all fillets is covered with the magnificent peelply. After curing the peelply is pulled from the frame, leaving a smooth and lightly textured surface with no sanding required.
The frame with the uncured fillets is mounted onto a table and fixated with heavy objects. In this stage it is still easy to bend the frame and I want to have it as straight as possible.
When you remove the peelply you have to apply a lot of force. The reward is a really cool display of physics: at the point where you pull the peelply from the epoxy a deep purple light is showing, a bit like the black light effect on white clothing.

After some final sanding and shaping the finished plug looks like this:

The plug is now ready to be laminated. All tubes are stuffed with foam or empty filmcans (these fit niceley into bottom brackets) to prevent the vacuum bag from beiing sucked into these tubes. Without this the bag would rupture at the tubes, not a very good thing for a vacuum bag to do.

And now up to next stage: laminating the frame.

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