Study where the cuts need to be and use a SHARP instrument. I use single edged razor blades....I buy boxes of ten, 10 at a time. If they show any signs of burring or dulling they hit the circle file. Sometimes rolling the blade along with downward pressure yields the cleanest cuts. I hold the two cut ends together and practice putting the two together exactly where I need them and then use a pencil torch with a longish flame, holding each half along side the flame shaft "just" until the plastic shows signs of sagging and then stick them together. I had to do several to get the ones in the picture. If they don't align just right, pull them apart while they are still hot and have at it again, trimming if necessary. Basically its a matter of practice, practice, practice.
