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How to make a sliced object manifold?

Message 1 of 12
9846 Views, 11 Replies

How to make a sliced object manifold?

I have come across a problem when slicing a large object for 3d printing. The object must be manifold/water tight so it can be made on a 3d printer.
Following a Plane Cut operation on my object, one side of a resulting sliced object remained "open" (not manifold).
As can be seen in the attached image (picture 1), one side was properly closed creating a tube-like structure, however the other end was not properly closed (picture 2). I can use the process ANALYSIS:INSPECTOR with "Flat Fill" mode selected to close the hole, however selecting the inner blue loop closes the inner part (picture 3) and selecting the outer blue loop closes the whole area (picture 4).
Can anyone tell me how to close only the hole between the blue loops so that it ends up looking like picture 1?
I have thought of doing a Boolean subtraction of the two surfaces but as far as I understand, that can only be done with objects that are already solid.

In you reply, please explain where to find the appropriate tools in the Meshmixer menus as I am very new to this software. (I'm using version 3.5.474).
Many thanks.


Message 2 of 12
in reply to: ludvikEV6EQ

There are situations where MM's PlaneCut fails to fill the cut. Since years I'm trying to find the reason. 

So my current understanding (literally on thin ice):

Seems this happens if the cutting plane exactly hits/shares the plane  where some existing edges are...


To fix it:

Inspector closes holes. Each hole is a loop of boundary faces. In your result of image2 there are two such loops. Imagine these boundaries are two banks of a river

You need to join them to one.  You need to build a bridge.


To do this:

- Go to SELECT

- Select a region right at the bank on one side. This selection needs to be not interrupted by not selected faces at the boundary;

- Do the same on the nearest by opposite bank (same needs as above) ;

- Run Edit/Bridge on this selection;

- Reduce Refine  in the bridge flyout to zero to get a flat bridge and Accept (if it fails you've missed to select some boundary faces);

> This joins both banks to a single boundary/hole you can fill using Inspector


Gunter Weber
Triangle Artisan

Message 3 of 12
in reply to: MagWeb

Hi MagWeb,
Thanks for the reply.
I tried to use the Bridge function as you suggested but I keep getting an error message (as shown in the attached images).
I thought perhaps that there were some faces I had not selected on the two sides I wanted to join, so I tried selecting the whole object, but that gave the same error.
Any suggestions?

Message 4 of 12
in reply to: ludvikEV6EQ

To make Bridge work you must not select both boundarie loops totally but select two regions at the boundarie only.

See: Helpdesk: Bridge

Gunter Weber
Triangle Artisan

Message 5 of 12
in reply to: MagWeb

Hi MagWeb,
Thanks, that solved the problem. It's a two step process; first make a little bridge and then let Inspector fill in the remaining hole.
Strange really, that trying to do it in one step causes an unknown error. I would have thought that such clever programmers (and this is an amazing piece of Software) could manage to fill the gap in a single step.
Anyway, job done.
So, whilst I have your attention, one other small question.
I can rotate the camera around the object in the workspace and zoom in and out, but I can't pan the camera left/right or up/down. Is there anyway to do this, or is this function not available?
If I rotate the camera underneath the object the floor/base of the workspace obstructs the view of the object. Is there a way to make the "floor" invisible to the camera?
(OK, that's two small questions 🙂 )

Message 6 of 12
in reply to: ludvikEV6EQ

You could also create a "big bridge" meaning that both boundary selections miss a little region on both sides only (let's say only 359 degrees of the full loops). But that (depending on the boundaries shape) might cause self intersections of the resulting mesh....

Well, you need to be aware that MM was developed by RMS as a research project . There are tools to be improved for sure (for development stopped at a working but not that much polished state) but it's a miracle and due to the great work of the team at Autodesk Research that it became such a great app. Improving workflows and tools should be a future task.

E.g: There's a SELECT tool "Join" which closes a gab between two boundaries with a single click (as you ask for) - but that tools doesn't keep the boundary faces and gives a "more or less" rigid solution.

A two step workflow of Bridge and filling via Inspector gives more flexibility and options (you might build several bridges to simplify complex holes) to end up with a planar fill when there are complicate boundary shapes (so it's the way I recommend).


By default (in "Fusion360" navigation mode > Preferences) you should be able to pan dragging the middle mouse button.

I recommend to use "Meshmixer" navigation mode instead as there are tool's where RMB dragging in this navigation mode allows special functionality (as ExpandModes in SELECT). About navigation hotkeys see menu: Help/KeyboardShortcuts.

There are modifier keys which work on both modes so I recommend to use those:

Alt + LMB-drag = Tumble

Alt + Shift + LMB-drag = Pan

Alt + Ctrl (Cmd on MAC) + LMB-drag = Zoom


To hide the floor (= "grid"):

menu: View/ShowGrid (which toggles the grid)

To hide the printer's floor:

menu: View/ShowPrinterBed (which toggles the printer's volume and base plane)




Gunter Weber
Triangle Artisan

Message 7 of 12
in reply to: MagWeb

Holy-Moly, MagWeb, you're a real mine of information 🙂 That solved two issues. Thanks.

So far I've been using Plane Cut to make the slices. However I have come to a part where I would really like to make a non-planar cut. A precise but irregular cut through the mold I'm making. What I would like to be able to do is draw a line around the object and make a cut through the object on that line. Do you know if that is possible?

Message 8 of 12
in reply to: ludvikEV6EQ


Let's say I want to cut off the bunny's head nonplanar:

You may use EDIT/GenerateComplex (see: Helpdesk: GenerateComplex).

To generate a complex you need FaceGroups first.

So SELECT (maybe using Lasso mode) the head of the bunny and run Modify/SmoothBoundary. This smooths the border faces of the selection. Make sure to have CreateNewGroups checked. This will result in a FaceGroup describing the parting line.

Now leave SELECT and run EDIT/GenerateComplex. The object will turn transparent and the FaceGroup's seam will be black. Hovering over the seam it'll get orange. Double click the seam to insert a parting surface and Accept.

The bunny is a complex object now. It owns non manifold faces where the parting surface touches the outer surface. Here three faces share the same edge. This is a mesh error in most third party apps. MM handles this.

The EDIT options on a complex object show SplitComplex. Click it and you will find the head and the body as two separate and manifold objects (You may discard the hidden source object and it's complex version now).



Gunter Weber
Triangle Artisan

Message 9 of 12
in reply to: MagWeb

Hi MagWeb,

I did try selecting an area (a band) around the object and using Smooth Boundary. However, the outside shell is made of quite large polygons and so Smooth Boundary still does not work very well; it produces a fairly jagged edge. Ideally I would like a method which does not rely on the existing polygons (such as Plane Cut), but I suppose there is not a free-hand version of Plane Cut yet.

I'm currently working on a workaround where I use Plane Cut to cut the object in to slices and then use Plane Cut on each slice in sequence to give a kind of curve with straight edges. It is difficult to be accurate with this method.


Message 10 of 12
in reply to: MagWeb

Sorry, No idea about it.

Message 11 of 12
in reply to: ludvikEV6EQ

Sorry for the delay (been on holidays).


Do you use PlaneCut in a literally cutting mode or only SliceGroups to get a group to split off via Complex. Not sure if I got you right.



You can get SmoothBoudnary to harsher smoothing with high Smoothness + low PreserveShape + high Iterations + more BorderRings and (if there are FaceGroups) PreserveGroupBorders disabled.

If due to poor resolution that still isn't enough refine the cutting region before ( using SCULPT an its RefineBrush or SELECT/Edit/Remesh(in BoundaryMode = FixedBoundary) 


For going the Complex route and the SmoothBoundary step don't select only a loop but the whole part (e.g. the head) you want to separate finally.


Another way is to do boolean operations. This cuts existing faces on a nonplanar surface (But personally I prefer the Complex way as Booleans are tricky):

Append a plane (> menu: File) to your scene.

Transform it roughly to a position where you want the cut to be.

SelectAll of the plane and run Deform/Wrap.

In Wrap double clicking on the selected surface creates a red handle sphere. Create several (but not too many) handles near the surfaces intersection line. Now dragging such a sphere deforms the surface. This way you can define a parting surface. 

Now still all selected run Edit/Extrude to create some rough hull object for the part to clip off.

Leave SELECT and copy the source and the hull object. Hide the copies.

Activate the visible source object and after that with SHIFT-click the visible hull. Run BooleanDifference on that pair. Hide the resulting object and show the other pair.

Again activate both and run BooleanIntersection on this pair.


Gunter Weber
Triangle Artisan

Message 12 of 12
in reply to: ludvikEV6EQ

I'm new at this so bear with me. I've read these extensive descriptions and operations and only have become more confused in trying to solve a problem similar to but simpler than the original problem described here. I have a hollow pineapple shape that I am trying to turn into a refrigerator magnet. I can slice and discard the side that I want to sit flush on the fridge but I can't seem to fill the hole with a flat fill making it manifold (if I understand the jargon). Bridging doesn't work presumably due to the bumpy surface of the pineapple. I KNOW it has to be simple but I just can't get to the last step for some reason. Erase and fill as well as bridging give me the same errors messages described here. HELP!!

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