Masking straight lines for painting

I use the Tamiya tape, and try to stick it down at two points- the beginning and end of the line.  I stick it down at beginning, then stretch it a bit, and hold it only at the end point, away from the surface.  Continuing to stretch it, I let the end of the tape approach the surface.  If it has sagged, I immediately pull it off and try again.

Head on out to your local automotive paint shop.  There they have some 3M vinyl tape.  If you watch Bitchin Rides,  Iron Resurection, or other of the custom car shows on cable.   They use these tapes to set the edges on masking areas.   The blue tape is 1/8,  the orange is 1/4.   Heck,  Tamiya also maes some 1/16 tape in white.

Like Don says,  set the edge of the area to be masked with the vinyl tape.  Set one end and pull taut, stretching the tape slightly.  Touch the opposite end down and press the tape down & burnish smooth.    If you are masking a curve, touch one end down and press down the tape as you reel it off the spool -- following your line.   Burnish smooth.

Backfill the area to be masked with a wider tape,  Tamiya yellow,  Frog Tape, or another Kabuki-type tape.   3M painters tape is also good,  but really hard to get a good straight paint-free masking line without using the vinyl as the edging.

Expert advice. The only thing I can add is that you need to be prepared to do it over a few times until you are really satisfied with how it looks, before you paint. No shame there.

I'l second Ed....3M or Norton "fine line" maasking tape.   available in several widths at most all auto paint suppliers.

Don’t use painter’s tape. I had it rip off a clear lacquer coat.

One problem I have had with the 3M blue tape is more adhesive residue left on surface than with the Tamiya stuff.

Thanks for all of the replies. I ended up applying tape, eyeballing a straight line, transfering to another piece of blue 3M tape, cleaned up the lines, cut out another mask and repeated the process until it was relatively straight across the fuselage. Made 2 masks and painted both. I also have a master mask so that I get duplicate masks every time. I started to get the white on, removed the mask, sanded it smoth. When I am back home I'll cut out more masks, then repaint until I'm happy to paint the dark blue at the end of the fuselage. I am building 2 of the same, so I want them to look pretty uniform. I'm happy because this is a first, I was able to not have a paint ridge on one, and on the other there was only a very slight ridge but was elimanted with a quick swipe of 800 grit sandpaper. 

I think I might invest in a laser level to see how that would work out. Apply the tape, level the model, use the laser level, draw a line on the laser line.