The challenge is trimming the arch rail to the exact width at the exact angle which, when combined with the bottom rail, will produce a square frame.
These things I know. The interior width of the gate should be slightly wider than the copper panel which is 24” (because I don’t want to mess with cutting the copper). The width of the arch must be exactly the same width of the bottom rail. The sides of the arch rail must be parallel. And the most important thing, the centerline of the arch rail will be in line with the centerline of the bottom rail.
So how to cut the arch? Simply use the bottom rail to line up the arch (top) rail.
First cut the bottom rail to width and draw a centerline. Set it on a cutoff sled flush the edge (hopefully square to the blade) of the rail to the edge of the sled.
Transfer the centerline from the bottom rail to the cutoff sled.
Line the centerline of the top and bottom of arch rail with the line on the cutoff sled. Fill the angled gaps at the top with the cutoffs from the glue up.
Clamp and cut and admire the results.
-- tim hill www.newcalshop.com