I’m curious how others have masked a straight line around a curved surface that also tapers.
The particular part is the nose of a 1/48 F-14 Tomcat in the mid 70s gray over white scheme. The standard spec called for the radome to be Insignia White part the way toward the nose, then Radome Tan from that point tapered to the nose.
Standard masking just doesn’t work as the tape cannot be kept straight while dealing with the decreasing radius of the taper?
Any ideas?
i have heard of people cutting out a circle in a sheet of card stock or whatever that is the right diameter and slipping that over the radome. THe exposed area gets painted and the card stock shields the rest of the radome. Does that make sense?
OWL
I usually start with a very thin strip of masking tape, in my case I swear by the Tamiya masking tape. Thin strips are easier to follow the curved lines. I then follow this this with a slightly wider strip until I reach the part which can hold a wide strip of the masking tape. This is also how I do sharp line camouflage.
As has been said, thin strips cut from Tamiya tape will work, automotive vinyl fineline tape will also do the same thing as well as conforming to curves a little bit better.
Another couple of things worth trying are PTFE tape (like plumbers use), or heatshrink tubing if the part is small enough (paint the forward section, slide the heatshrink tubing over & paint the rear section).
[dto:]
I always paint mine from the point back. So I would paint the whole thing radome tan and the white after. That way you can put the tape on the taper side so you can start with a wide piece. Keep the tape pulled tight while you mask. It’s just reversing what side of the demarcation line your tape is on. Easy to get a line. I just callapse the excess tape down to the radome and make sure everything is covered.
My other method (because every paint job is different) is to just wrap the tape all the way around the radome and then cut a straight line in it afterwords. I do this by putting the dome flat side down on the table and putting the knife on a book or whatever to get the blade to the right height and then I turn the dome against the blade once the blade is secured where I want it. this can work great if you have like say 2 prop spinners and you obviously want them the same.
Hope I made sense there. 
I usually use a combination approach. First I use extra fine masking tape to make the contour, then liquid masking solution to cover the bulk of the area behind the tape. The tape gives the smooth edge, and the liquid mask makes sure nothing else gets painted that shouldn’t be.
Rich