I got frustrated by the lack of compact early game production of mk 3 belts and made this. If it's not very efficient this is my first blueprint that I've ever tried to make this compact.
In: 6 iron/s, 1 copper/s
Out: 22 mk3/s, 44 mk2/s (if mk3 is full), 44 mk1/s (if mk2 is full)
Machines/parts:
9 arc smelter
11 assembler
255 belts
35 sorter mk1
13 sorter mk2
3 tesla tower
3 depot mk1

Only mod I built this with that might cause this to be incompatible with vanilla is blueprint tweaks but worse comes to worse there's one spot on the iron line that's broken and needs to be rebuilt by hand (see the belt bending guide by Ludus Machinae on YT)