Bending acrylics is a bit of an art, go to your local glass shop and ask them if you could buy or have some of their small scraps to practice with. The best tool For heating the plexi glass is a heat gun. be careful not to hold the heat gun too close to the material, keep it moving, and like Miker says be patient. Another thought I have is to cut a piece of plywood to the shape you'd like, cover it with soft cloth, and use it to re-shape your windshield.

I've worked in a glass shop for approximately 10 years and played around with bending acrylic occasionally. I believe that as long as you don't overheat the material it shouldn't get brittle. One thing I'm not 100% sure of is whether motorcycle windshields are made from plexi or lexan, I would think lexan. Either way they should be very similar to work with, the key is practice first so you don't wreck your windshield.

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