Sunday, 25 July 2010
The glaringly obvious thing that I need to make for the BMW at this point, is the seat hump. While most people who have seen the motorcycle in the flesh have expressed approval, their ideas about what the rear of the seat should look like have varied considerably. While it's quite a short looking motorcycle, my feeling is that proportion is a more desirable quality than shortness, so while the rear end styling needs to have an element of "short" about it, it also ought to look like it belonged there. Given that I'm using a (more or less) standard BMW frame, with a standard BMW fuel tank, forks and wheels, then the seat hump is what has to make the motorcycle stand out. Which is a lot to ask from a seat hump...
Bearing all that in mind, I chickened out of making the seat hump for a bit and made this battery tray instead. Once you've established that it's a tray, and the battery goes in it, there's not a lot left to say about it. It's going to accommodate a YTX-9 gel battery, led on it's side, and the standard BMW ignition switch, which will end up positioned under the left lower rear of the fuel tank. where hopefully it'll be discrete, but accessible. With the tray made, I drilled it to accept some mounting bolts, then made some brackets to mount it from. I made the brackets from some 3/4" x 1/8" steel strap. Bolting the brackets to the tray, positioning the tray, and then welding the brackets to the frame made the task relatively easy, and ensured that all the holes lined up.
All relatively straight forward and quite soon over and done. Which meant it was time to tackle the seat unit.
Rather than a card template, I cut out a piece of steel and drew a profile straight onto that. To my mind, this is the difficult part, getting a clear idea of the shape that you're going to make. Copying another shape is one thing, evolving the shape, working out how to make it, and then making something that matches up with your concept requires a different level of skill. A simple flat template can look ungainly, but adding some shape to it alters the profile slightly, and makes quite a dramatic difference to the way it looks, which means that the template has to drawn with that in mind.
To get the shape into the components of the seat hump, I think I used a ball peen hammer, the arbor press, a bench top English wheel, a big rubber hammer, a piece of timber , and my thigh, with the moral being that whatever works, is "correct".
After what might have been four hours of work, the seat unit looked something like this. Somehow it ended up being a lot more rounded than I meant it to at the rear, which is slightly problematic. I'm a little disappointed that the rear end isn't as flat as I wanted it to be, which is colouring my judgement of the overall effect. It also begs the question, how am I going to mount the rear light? The idea of heat forming some red perspex to the shape of the seat hump and then cutting a window in the hump and having a flush mounted lens for a built in light, possibly using LEDS as a light source crossed my mind, but I don't really want to do that, because I've done that sort of thing before, and I don't really enjoy it. It's a thought, but it's a last resort sort of a thought.
I think that by the time the seat unit has foam and upholstery, it ought to flow reasonably well with the tank, and everything below that will be quite skeletal and exposed, especially if I get a bit more vicious with the engine castings. I'm giving some thought to what I want to do with the frame, even going as far as buying a tapered reamer with a vague idea of making some Tony Foalesque tapered bosses to mount some frame braces on. I also ought to start looking for a bent, busted, or otherwise discarded Suzuki Bandit frame that I can cut the frame splice joints out of with an eye to grafting them into my frame so that the oil filter can be accessed without removing the engine from the frame. Though, other more radical, Team Incomplete inspired, ideas wander across my thinking spaces from time to time....
For now, finishing up the hump and another trip out into the daylight are the priorities.