The mould is just chipboard but it’s important to get the headtube accurately aligned.
I lined up the centre drill to my mark, indicating the internal headtube centre line.
And then drilled.
I drilled both ends: for the second end, the centre line has to coincide with the drill axis, so I lined up the first end with the lathe tailstock.
I’ve settled on a new design, after much toing and froing. I’m trying to get the advantage of bigger wheels, a lower seat and bottom bracket, as well as lighter weight, squeezed into the new prototype. To fit a low seat and rider around the larger wheels requires curvaceous framework which itself justifies the efforts of using composite construction, over my usual ali tubes, which are difficult to bend. Two further advantages are that once the moulds are made, this is a more readily repeatable process than ali tube fabrication and it should be considerably more structurally efficient, i.e. lighter.
I’m currently making the soft tooling ie. moulds out of chipboard filler. The first pressings will be in S ‘glass with some carbon reinforcement. Ultimately though unidirectional carbon will be used. The pictures show the paper templates stuck on the main moulds part and outlined with a Stanley knife. That’s the start of a three day mould-making process.
I’m calling it the low profile prototype. We’re definitely getting there but it’s two steps forward and one back.
The carbon prototype and a rethink of the Switch function has meant the prototype is going to be quite different. I’ve also moved to a new workshop.
I’m writing a lengthy article for the BHPC magazine, Issue 120. (http://www.bhpc.org.uk/magazine.aspx) about the long road to a viable Switchblade. To be published in July or August.
I’ve a new design proposed for the row power (arm propulsion) system. I think I can essentially package most of it below the top of the headtube. That would make things look a bit sleeker. But it is not straightforward to do and will take a bit of development. In the meantime, here ae some pics of an earlier prototype – perhaps the nicest looking one I made but it had a few major flaws – looks aren’t everything.
Extensive discussions with various experts have made me rethink where I am with fabrication techniques. It looks like the new frame is going to be a mixture of ali and carbon. I’m trying to get there quickly but still have something that looks presentable. I can certainly save weight with carbon but making it strong enough is something I’ve previously paid inadequate attention to. Here’s a bit of frame in my jig.
I’m reverting back to aluminium after experimenting with carbon; my workshop carbon fabrications were structurally adequate but didn’t look very neat. I see carbon as a great option for a lighter frame but I still have some basics to sort out and machining aluminium will help to address these more straightforwardly and give a production ready finish which the carbon can only deliver with more work and investment.
I’ve sorted out all the major design issues with the last prototypes (actually, the last eight or nine prototypes). What I mean is I’ve got the functionality of the Switchblade to work with a viable frame geometry for both manoeuvrability and speed (seat height in the low position is about 12”). From now on, its nearly all detail design. But that’s still a lot of work. I’ve been designing a new compact front fork, as there is quite a lot to squeeze in at the front end. The back end is now reverting to a standard dropout arrangement so at least I don’t have to modify my own hubs. I’m planning on a completely symmetric frame design with a single central tube for the lower g frame and smaller tubes on both sides for the seat frame.
Dave Mc Craw’s blog provides some really useful insights into cycling performance. His basic energy and performance articles highlight how recumbents and upright cycles compare, in terms of effort and speed.
There is a big difference in adaptability of individuals and much of the effect can be eliminated by training or conditioning but it seems that the recumbent position makes cycling harder work for some: http://www.ncbi.nlm.nih.gov/pubmed/16222538.