Here are a few photos from the cutting and fitting of the wingtip lens work.
The first shows the lens blank after it has been cut in half with a Dremel tool cutting disc.
This shows the blank setting on the tip with tape outlining the cutout area plus about 1/2 inch.
This shows cutting the blank along the tape line to get the lens about 1/2 inch larger than the final size. This gives you room to adjust as you work it into the final size. I couldn’t find a better way to cut the plastic. The wheel both cuts and melts the plastic, with the melted part breaking off easily leaving a fairly smooth edge.
After cutting the lens is fitted to the opening and you can see excess I had to tweak. Notice the mark on the lens and the tip so I could get it back in the same position after trimming.
I now put tape along the lens marking the trim cuts to edge of the tip where the lens has to fit.
I then used a sanding disc to remove the plastic to the tape line.
Then I did the final tweaks by hand by sanding the edges on the flat bench top with emery paper. By taking just a little at a time and doing many fittings, you can get good results. While moving the lens over the sandpaper I kept the lens in its final shape by bracing the open end with my hand. This results in a contour of the edge that fits the tip contour.
Here are two shots of the final result. I bet I had to fit each lens at least 50 times to get it like this.
Every adjustment on a side effects the other side so it is best to go real slow and do a lot of fitting.