Hi Mike,
Not sure exactly which lines you're referring to, but I just had a bit of a scribing 'exercise' on a CF-5 that I'm building. I got some good advice that might help:
- get some 'Dymo' tape. It's the tape they used to use in those older label-making machines (the kind that 'embossed' the letters into the heavy tape). Stationary store should have it. It's thick and has a peel-away sticky backing that works great to hold the tape in place. You can pull a scriber or knife along it really well and it goes around fuselage curves quite well. My F-5 was in 1/72 so it was a bit tight, but worked well.
- I also got some advice to 'roll' a curved blade (like a scalpel blade) over the line. This works really well on fuselage curves. At a minimum, it creates a bit of a channel so that you can pull a scriber through. The blade creates a bit of a ridge that I just buffed away with a bit of a scouring pad.
- Last thing I learned (discovered this on my own) is that electrical tape can work as well. This isn't nearly as thick as the dymo tape, but it's more flexible for doing 'rounded' corners or lines. If you cut a thin strip, it can be twisted around fairly well. You can drag the scriber along this line, but GO SLOW and LIGHT! (several passes if needed) It's not as rigid as a ruler or the dymo tape, but should get the job done if you have patience and a light touch.
Hope that helps! Good luck!
Murray