I did mine on a bandsaw with a fine tooth blade. Like was said, I made a template of the shape I wanted, covered both sides with blue painters tape, and traced the template on. Fed the windshield thru the saw slowly. Finished it off with a palm sander. no one ever knew it was cut.

 

I just cut a windshield (1 week ago) using a 32 tpi jig saw blade. What I did was to tape but sides with painters tape first and then put duct tape over it as an added precaution against scratching. I then used a disc sander to take it down to the line. Next I used a sanding block and used grits 180, 220, 320 and 400 to make sure I had all ripples off of the top edge and slightly relieve the sharp edge.. Final step was to use a flame to slightly melt the edge for a finished look.

Looks just like it came from the factory. -- When cutting, pay close attention to what the plastic is doing -- going to slow or to fast is not good. Too fast tends to chip, too slow tends to melt. Have a sharp blade

 

Here's a good demo to cut down a windshield.


I followed this when I cut the shield down on my old V-Star a couple of years ago. Worked out perfect.