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Matt Cartney 31 Dec 2008 11:41

Making your own plastics
 
Hi folks,

I am (again!) toying with the idea of making a screen for my XT. I've made a couple in the past out of Lexan, which is very tough and easy to form. However, I've made the mistake of making them too big and unweildy and both of them bit the dust in crashes. This time I'm thinking of making a small rally screen which will be not much bigger than the plastic headlight surround already on the bike. It will have a small lip to kick up the wind a little and be attached to the plastic headlight surround.

The question I have is: What should I make it out of? I could use Lexan again, but it is excessively stiff and I don't need it to be see-through. In fact I'd rather it was opaque - preferably white. The same sort of plastic they make dirt bike plastics out of would be great. Where would I get something that was cheap, easy to form (with a heat gun perhaps) and not as brittle as perspex or lexan? Fibre glass is just way too much of a hassle.

Anyway, hope somebody can point me in the right direction.

Cheers,

Matt :)

tenere_rider 31 Dec 2008 12:45

Polypropylene
 
Could I suggest to first play with a mock up of the screen first, including a dummy of you... or maybe the real you! Just kidding! Then blow fan forced air against fairing and rider shape with a smolke trail to indicate its track. The deflected air should just strike the top of your helmet, Now as for polypropylene ... it's tough, flexible, but without carbon black or other colorant is somewhat UV sensitive... this would not be an issue if you want to peep over the top. As for fabricating it, you could buy it in sheets, or even cut up an existing container, and being a thermo plastic can be heat formed. Your problem will be shaping the convex curve of the shield which will "fight" the concave shape of your "air kick up" top edge. It will be a bit of work but I think the best and most symmentrical way to achieve this will be to construct male and female moulds from construction plywood where there are flat planes. Use polyester car "bog" and ribs at the curved profiles, gussetted to maintain the shapes during the squeezing process. As a high school tech teacher we use ovens for heating thermo plastics... they are about the size of pizza ovens... now there's a thought! Heat the plastic pizza until floppy then wearing gloves, race it to with the drill press and use the chuck to apply the sqeaze to the strengthened top mould, the plastic between the moulds on the drill press table. Wait to cool, remove from the mould, apply a topping of your choice then wash down with a cold beer! :thumbup1:

Matt Cartney 31 Dec 2008 20:27

Thanks for that, it's good info. I hadn't thought of rescuing some polypropelene from something else to make my screen. Will have a poke round the garage and see if there is anything knocking around. That way I can even make a couple of trial screens and it won't matter if they are rubbish. And will definately wash each one down with a couple of cold beers!

Matt


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