Automate adding a Surface on a cut Mesh I am completely new and following some tutorials. I am preparing a Abyss Walker from DS3 for a 3D printer and splitting up the figure. I wonder is there any tool or option to automatically add a surface to a split Mesh?



As you can See I split it to reduce the amount of supporting structures. It would be nice to avoid the hollow (pun not intended). Would be cool if there is an option to add surfaces where I cut it.
Try the Bisect Function

3D View > Mesh > Bisect, requires a Face Selection



This allows you to split the mesh along a plane you can define by dragging, or numerically. If your Operator Panel is not open, hit F6 to show it.
It come with a bunch of useful options, like 


Fill, which fills the cut edges with faces
Clear Inner/Outer which remove one or both sides of the cut
Axis Threshold that gives the cut adge some fuzzines in where the cut-off happens.