Sunday, 12 May 2013

Construction begins

in my last post i said I had begin cutting the templates for the chain stays.  The original XR2 design calls for these to be made from aluminium, and while it's possible for me to do this, I had thought about making them out of carbon.  My thought was to make a plywood and balsa former that was to be wrapped in carbon.  But when i started cutting the wood, I realised what a nice bit of wood I had.  It's 6mm modeling plywood, birch I think.  So by way of an experiment I'm going to attempt a wooden swingarm.

I've deviated from the original design again...  The original XR2 has a chain wheel in the middle of the bike, so the right chainstay is set in behind the sprocket, and above the bottom bracket.  As I'm dispensing with this sprocket, I've made the chainstays symetrical.  As a result, I can make a jig and use it to form both sides.

In order to stop the rear wheel rotating and stopping the roller brake from working, I've recessed some lumps of metal into my chainstays.  The epoxy is curing on these just now.  The plan is to add a couple of layers of ply to the chainstays, then join them together in the middle to take the suspension pivot.  I'll be adding a few layers of varnish to lift the colour of the plywood.  This is an experiment, so I'll see how it goes.

Of course, now I have chainstay and frame templates made up, I had to make a mockup using the other components, clamps and imagination.  Ignore the headtube height and angle - that's the angle it wanted to wedge itself in at.

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