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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): Portion of deck with required slot marked

Wireframe image of the same area, with duplicated and separated 'slot object in the required location: Wireframe view of the deck with a copy of existing mesh duplicated and moved into place

There may of course be other, better, or less 'manual' ways to do this...

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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.

enter image description here

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

enter image description here

  • 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.

enter image description here

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  • $\begingroup$ Alright, so make a small rectangular surface, apply the Bézier curve and extrude down, for the first step? And then what, apply that to the piece I have? I don't particularly want to start over, it is as I want it except for four small areas. Sure, I can try that. As for tedious: yes, I agree; but it's worth knowing how to do that just the same. $\endgroup$
    – K.G. Feuerherm
    Apr 30, 2020 at 16:26
  • $\begingroup$ I didn't use any bezier curve, just the Knife Project tool to make the hole, then extrude inwards, then extrude it down. $\endgroup$
    – moonboots
    Apr 30, 2020 at 16:33
  • $\begingroup$ 1) The whole point of the Bézier curve is for it to be a smooth cylinder. 2) How do I get the bottom face and sides? (Never mind, from the previous question I guess extrude the edges down, turn it over, and fill the face...?) But I get the impression you're suggesting I start over.... 3) Keep in mind this is a static object, not something I'm going to animate, so if I can just finish it and print it, I'm done, whether or not I could have done it with fewer vertices. I have other objects I can apply different methods to. $\endgroup$
    – K.G. Feuerherm
    Apr 30, 2020 at 16:47
  • $\begingroup$ Update: First, I tried using knife project on a surface and it didn't do a very nice job at all. It misplaced some things, and even those placed in the right place are overly simplified and do not look nice, unfortunately. Then I decided to try the same thing on a square plane (simpler topography) and leave cutting the outline to the end. The results seem more promising, this time. $\endgroup$
    – K.G. Feuerherm
    Apr 30, 2020 at 20:24
  • $\begingroup$ Once you've used the Knife Tool project you need to bring some corrections, us the Knife tool to create new edges (K to activate, C to cut orthogonally, Z to cut through), or join some vertices with J, etc... $\endgroup$
    – moonboots
    May 1, 2020 at 5:59

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