Duplicate mesh section and merge Following up on a question I opened up earlier (Joining more objects breaks fill), I have a mesh produced by repeated application of boolean modifier 'difference'. (This represents a Type VII submarine deck with sea water cut-outs to be 3D printed in due course.)

In a few cases, however, I was not able to get the booleans to work despite moving the modifier objects slightly, re-editing them, applying various suggestions found on the internet, etc. Fortunately, the number of problems is small (4 items) in comparison with the whole project (several hundred), and in each case I have a similar slot nearby which I can theoretically reproduce if I can figure out how.

I am wondering about doing these last four manually by copying and pasting in existing sections of the wireframe (for example). I am able to select a section of wireframe, move it to the right place, and separate it as a separate object (if need be), but I'm not sure how to paste it in so that it creates the proper intersection points so that I can cut out top and bottom faces and end up with holes going all the way through (as well clean topology).

What I have now, with one of the extra required slots marked (by Bézier curve object of the type I extruded to make the original boolean difference modifiers):


Wireframe image of the same area, with duplicated and separated 'slot object in the required location:


There may of course be other, better, or less 'manual' ways to do this...
In my opinion your method is too tedious and your topology has too many vertices and ngons. What you should do in your case is:


Create a module like this one.





Enable the Snap tool (or press Ctrl) in vertices mode and enable the Auto-merge option.





Duplicate the module as much as you want, move on the X or Y axis (GX and GY), snap and auto-merge will help to make them stick each-other. Give it a Subdivision Surface modifier (and Shade Smooth) to make it look smoother.