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[cris]

I dont think you would get away with using perspex without a frame around it with such a large size. It would actually be possible to bend the perspex slightly to make it more rigid but it would be a lot of mucking around and would be very easy to stuff up. You might also get away with using thick perspex 8-10mm but that would be very heavy and expensive and may not be any good(maybe?)

Personally i would go for perspex with a small metal frame around it to stop it distorting. You need to be careful drilling perspex with a standard drill bit as it can crack pretty easy. There are special bits designed for drilling perspex that would probably be worth buying.