First, use the board as the base at the two right angles above, and then use an arc angle to fix it on the finished board with a nail gun. The inside and outside are operated in the same way to form an arch, and the hollow between the two arched semicircles and the wall is fixed with equidistance wooden square dragon bones.
Draw a line (about 5cm) on the gypsum board with a paper cutter (note: the line is used to bend the gypsum board along the arched arc, so don't cut the gypsum board).
Apply glue to the non-scratched side of the wood square and gypsum board, and then fix the gypsum board on the wood square with glue and nail gun. This completes the basic structure of the arch.