please post a file. generally i think what you want will look completely different than you might expect. for the lines to be perpendicular to both curves you might have intersecting parts or at least accelerated decelerated parts where points are denser or wider on the top or on the bottom. having the geometry distributed rather more regular would of course break your wish to have them perpendicular… but i am just dreaming that up now without a file.
i tested something with quick curves to prove the problem, dividing the lower part equally and hand draw curves with snaps set to perpendicular you see that after the third curve from the left you alreay have a huge discrepancy. is that what you want?
