-
I often make them in 5mm ply or thin MDF, sometimes start with a paper template and transfer it to thin board. It's still a job with a saw and plane to get a really good fit. The transfer stage gives you a chance to tidy everything up once you know it fits.
It helps if you plaster the walls flat and sloping in slightly each side! Looks like the decor is already done though.
Sometimes you can chisel a channel for the board on either side and fill to the face of it. The join shows less there than it does on the board face.
Airhead-
Thanks, but damn, I already filled in the channels where the old one came out (took a chunk of the corner with it) but I could always channel a bit out again. I think they do taper in slightly towards the window so that's a plus. The whole room may get new plaster at some point so it can always be covered over then if I do bodge it.
-
Channeling method worked well, so thanks! Certainly should look a lot better than my attempt at scribing would have. The filler I had put in already was not all wasted, made it pretty easy to cut a straight-ish channel which should make the clean up easier
Polygon
How should I be scribing a new cill (I already have it) to fit in here? Scribe on to scraps of plywood, cut them out and then use them to scribe the line back to the cill?