I have a one piece clear Canopy. I want to Paint black 2-3mm lines representing the Frame. I have thought of scribing (scraping) the design I want then painting between, I'm hoping the scribed lines will prevent the Paint from bleeding. Then I thought I would just tape it up but, Paint always goes underneath. What is the best way??? What do you guys do???

I plan on using a Polycarbonate Paint called Pactra, clear body paint for RC cars.

Get yourself some "liquid mask", spray the inside, cut the design of your frame, peel away where you want paint and go to it. Mfg. by Bob Dively. I have used this stuuf for years and it works GREAT.
Steve

Or go to an auto paint supply and ask for "thin line" stripping tape.
You can get it in 1/16- 3/8 width, I use 1/8. create the spaces you want painted with this flexible, fine edged tape, then tape off the other areas with regular masking tape. about $4 a roll

Well I decided to use a good quality scotch tape. The Elmer's invisible. It was quite easy to see though
I was able to get the tape to stick real well, yet it pulled off clean. No bleeding at all, very clean and straight lines, I'm real happy with it.

You can also use Long Mask. It is a blue tape that does not bleed any paint and it does not lift up any paint if you are applying paint over paint. It is available at the Home Depot. Been using it for years and nothing but complete success. Good Luck, Dave.