a vertical bandsaw will do.
i wanted a new seat frame that was lighter and incorporated a n2o bottle mount so...
i bought some 2x4x1/4-inch aluminum angle for the stringer mounts. the curves were drawn by tracing a stringer washer
which i cut up using my trustry craftsman band saw
i added two sections of 2x2x1/4 aluminum angle for the braces. at some point i'll take these to a friends shop to add windows to take some more weight out