I'm running into an issue which seems impossible to fix. The fact that there is an option for fixed, optimised or random start points is very convenient, but there is something that doesn't make any sense. When I select 'optimise', the end of the inner perimeter touches the start of the outer perimeter (= very short travel move). But when I select 'random' (to make sure there is no line shaped seam), the end of the inner perimeter is on a different place than the start of the outer perimeter. It looks like the start of the inner as well as the outer perimeters are also random, but relative to each other, which is something I can't imagine any useful application for..
This end to start travel move creates a tiny gap at the start of the outer perimeter. Which I think is caused by the filament pressure that drops when the printhead travels from the end of the inner perimeter to the start of the outer perimeter.
These are the gaps I mean.
I have tried A LOT of settings, values and combinations to try and solve this: wipes, retract wipes, coasts, inside out and outside in, (un)checking "only retract when crossing open spaces", extra restart primes, slower outer perimeter, linear advance. Nothing works. Funny though: an old version of cura (15.04.06) creates an almost invisible seam with no adjustable settings. So this is what I still use for certain picky customers.
-> The solution is to have the end of the inner perimeter touching the start of the outer perimeter, also when 'random' is selected.
-> Also another possible solution is an adjustable X millimeter overlap between the start and end of the outer perimeter, closing the visible hole. You could see this as a wipe-like action, but instead this overlap function needs extrusion, where a wipe doesn't extrude.