Flipping normals in blender

NormalsпѓЃ

The Normal Edit Modifier can be used to edit normals.

The Weighted Normal Modifier can be used to affect normals by various methods, including Face Strength (see below).

You can also copy normals from another mesh using Mesh Data Transfer ( operator or modifier ).

FlipпѓЃ

Mesh ‣ Normals ‣ Flip

This will reverse the normals direction of all selected faces. Note that this allows you to precisely control the direction (not the orientation, which is always perpendicular to the face) of your normals, as only the selected faces are flipped.

RecalculateпѓЃ

Mesh ‣ Normals ‣ Recalculate Outside and Mesh ‣ Normals ‣ Recalculate Inside

Shift — N and Shift — Ctrl — N

These tools will recalculate the normals of selected faces so that they point outside (respectively inside) the volume that the face belongs to. The volume does not need to be closed; inside and outside are determined by the angles with adjacent faces. This means that the face of interest must be adjacent to at least one non-coplanar other face. For example, with a Grid primitive, recalculating normals does not have a meaningful result.

Set from FacesпѓЃ

Mesh ‣ Normals ‣ Set from Faces

Set the custom normals at corners to be the same as the face normal that the corner is part of.

RotateпѓЃ

Mesh ‣ Normals ‣ Rotate

This is an interactive tool. As you move the mouse around, the selected normals are rotated. You can also invoke the Rotate Normals tool by pressing the Rotate transform key R , followed by N .

Point to TargetпѓЃ

Mesh ‣ Normals ‣ Point to Target

All selected normals are set to point from their vertex to the target after confirmed by Return or LMB .

A target is set by the keys:

The mouse cursor M

The object origin O

The cursor (set at this click) Ctrl — LMB

A mesh item selection (set by this click) Ctrl — RMB

The tool operation can be modified; if one of the following keys has been previously pressed:

All normals will point in the same direction: from the center of selected points to the target.

Each normal will be an interpolation between its original value and the direction to the target.

The normal directions are reversed from what was specified above.

Will reset the custom normals back to what they were when the operation started.

MergeпѓЃ

Mesh ‣ Normals ‣ Merge

Merge all of the normals at selected vertices, making one average normal for all of the faces.

SplitпѓЃ

Mesh ‣ Normals ‣ Split

Split the normals at all selected vertices so that there are separate normals for each face, pointing in the same direction as those faces.

AverageпѓЃ

Mesh ‣ Normals ‣ Average

Average all of the normals in each fan of faces between sharp edges at a vertex.

Copy VectorsпѓЃ

Mesh ‣ Normals ‣ Copy Vectors

If a single normal is selected, copy it to an internal vector buffer.

Paste VectorsпѓЃ

Mesh ‣ Normals ‣ Paste Vectors

Replace the selected normals with the one in the internal vector buffer.

Smooth VectorsпѓЃ

Mesh ‣ Normals ‣ Smooth Vectors

Adjust the normals to bring them closer to their adjacent vertex normals.

Reset VectorsпѓЃ

Mesh ‣ Normals ‣ Reset Vectors

Put normals back the to default calculation of the normals.

Select by Face StrengthпѓЃ

Mesh ‣ Normals ‣ Select by Face Strength

Another way to affect normals is to set a Face Strength on the faces of the model. The Face Strength can be either Weak, Medium, or Strong. The idea is that the Weighted Normal Modifier can be set to pay attention to the Face Strength as follows: When combining the normals that meet at a vertex, only the faces with the strongest Face Strength will contribute to the final value.

For example, if three faces meet at a vertex and have the face weights weak, medium, and strong, then only the normal associated with the strong face will be used to set the final result.

Use the submenu to pick one of Weak, Medium, or Strong. Then this tool selects those faces that have the chosen face strength.

Set Face StrengthпѓЃ

Mesh ‣ Normals ‣ Set Face Strength

Use the submenu to pick one of Weak, Medium, or Strong. Then this tool changes the Face Strength of currently selected faces to the chosen face strength.

© Copyright : This page is licensed under a CC-BY-SA 4.0 Int. License. Last updated on 02/15/2023.

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Flip Normals (inverted faces)

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In newer versions of Blender the previously available Tool Shelf buttons Flip Direction and Recalculate, typically used to flip inverted surfaces that made meshes appear inside-out, have been moved to the main Mesh menu upper-left of the 3D View. As the option is now context sensitive it only appears as a menu option in Edit Mode.

Design note: the Mesh menu is specific to Edit Mode and does not appear unless that particular editing context is active.

Flip Selected Faces

To access the option and/or correct an inside-out or inverted face, first select the errant mesh element in Edit Mode [1] (using vertex, edge or face) and from the Mesh menu upper-left click Normals [2] then Flip [3] from the options that appear – Mesh » Normals » Flip. Alternatively use Alt + N to access the Normals context menu then select Flip. The highlighted inverted face/s will immediately invert based on their current orientation.

Design note: when selecting errant faces using vertices or edges make sure all component elements are included to the degree that the inverted faces highlight.

The option to flip or invert faces [1] is an Edit Mode option only (accessible only when editing meshes), click Mesh » Normals » Flip [2 & 3] with an individual face or group selected.
To fix inverted faces, or meshes that appear inside-out, in Edit Mode use the Flip Normals feature available in the Normals submenu — Mesh » Normals » Flip Normals. —>

Recalculate Faces

As an alternative to selectively inverting faces, or re-orientating a large mixed selection so everything points in one direction, inwards or outwards, use Recalculate Outside ( Shift + N ) or Recalculate Inside ( Shift + Ctrl + N ) options. To do this and force the orientation in one direction or the other, in Edit Mode select the entire mesh ( A ) and access the Mesh menu. Here select Normals » Recalculate Outside to flip faces/selections outwards, or Normals » Recalculate Inside to invert selections inwards – Mesh » Normals » Recalculate Outside/Inside.

Design note: in previous versions of Blender Recalculate tended to orientate faces randomly depending on the predominance of inwards or outwards facing surfaces prior to use. For Blender 2.8+ this is no longer the case, Recalculate Inwards and Recalculate Outwards forceably re-orientate selections based on the option selected, either in or out but not both.

For instances where surfaces are randomly facing one way or the other [4], or there are too many to select and manually process, use Recalculate Inwards/Outwards [5] to force everything to face the same direction, in or out, regardless – make a selection (individual, group or all) then click the Mesh menu, Normals then Recalculate Inwards/Outwards.
When a mesh contains many inverted faces their orientation can be forced to face inwards or outwards using the Recalculate Inside and Recalculate Outside options also available under the Normals submenu — select all the errant faces (or everything) and click Mesh » Normals » Recalculate Inside/Outside. —>

Face Orientation

To assist determining which way a face might be pointing, especially if Backface Culling is not disabled in Viewport Overlays or Viewport Shading options (depending on the viewport display mode) or a given materials Settings properties, Blender 2.8+ includes an option to colour tint faces based on their orientation, RED for surfaces pointing inwards and BLUE for those pointing outwards, making it much easier to see at a glance what’s going on, which then allows for individual faces to be flipped or recalculated as needed. To use, click the Overlays button upper-right of the 3D View [6] and from the menu select Face Orientation [7] – Overlays » Face Orientation. Everything will immediately tint blue/red based on their orientation. To disable, repeat, select Overlays » Face Orientation.

Design note: if X-Ray ( Alt + Z ) is active for any of the Viewport Shading modes, Wireframe, Solid etc., Face Orientation won’t work.

If Backface Culling is disabled (off) it can be difficult to determine which way a given surfaces is pointing because both front and back of the mesh are the same. In this situation using the Overlays [6] setting Face Orientation [7] can help as it tints surfaces based on their orientation, inwards or outwards.

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how to flip normal direction in blender

I am following a blender beginner tutorial by blenderguru and he is me how to make a doughnut.so we wanted to make sprinkles and he said we needed to change normal direction to face inwards. in his blender(which is an older version), you can do that by selecting the ‘shading/uv’s’ section in the tool bar. however, the new version doesn’t have it there. Can someone tell me where it might have been moved?

anyhelp will be appreciated

3 Answers 3

It would be better to say which blender version, rather than «the new version». It is there in Blender 2.79 in the same place you mentioned under Shading/UV tab. The tab will show up only when you have your doughnut in edit mode.

Flip Normals

(re the title «How to flip normals»)

In edit mode, select the faces you wish to flip normals and

Mesh > Normals > Flip Normals

Select all vertices in Edit Mode and hit CTRL SHIFT N . That should calculate the normals inside.

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When we start to learn modeling in Blender, we will come across multiple problems with our mesh. Anything from inverted normals, making our shading look off to lose geometry and gaping holes in the mesh.

Here is a list of the most common problems that you may come across.

• Inverted normal
• Zero area faces
• Unconnected edges, vertices or faces
• Loose geometry
• Intersecting and self-overlapping geometry
• Faces bending incorrectly
• Non-manifold vs manifold meshes
• Gaps in the mesh
• Messy topology and mesh density problems
• Vertices or edges without faces

Let’s explore these mesh problems in turn and learn how we can solve each one of them.

What is Inverted normals and how to fix them in Blender?

In blender when we have inverted normals our mesh is going to look odd. Here is an example of some faces on a cylinder with flipped or inverted normals and smooth shading.

To solve inverted normals, in most cases, we can go to edit mode, press A to select everything and follow up by pressing Shift+N to let Blender automatically recalculate normals. This solves these kinds of errors in most cases.

A face has two sides, one front and one back side. It is important for the shading that the faces point in the correct direction. We can visualize the direction of the normals in a couple of ways.

The easiest is to, in edit mode, go to the overlay menu in the top right corner of the 3D viewport and check «face orientation» located in the geometry section.

This will color the front side blue and the back side red of all faces.

If Blender can’t automatically recalculate the normals, sometimes we need to manually select the faces causing problems and flip them manually. We can do this by selecting the faces we want to flip, press Alt+N to bring up the normals menu and choose flip.

Blender always tries to guess what direction a normal should be facing every time we add geometry, but sometimes it gets it wrong and in those cases this kind of problem can occur. Just be mindful of the shading and this shouldn’t become a major problem that is hard to solve on even a complex mesh.

What is a zero-area face and how to we fix them in Blender?

A zero-area face is a face that does not have any area. In Blenders default shading mode, we can’t see them, but when we model, they will be taken into account during modeling.

To detect zero area faces, follow these steps:

• Go to edit mode
• In the top right corner of the 3D viewport, expand the overlay menu
• Locate the mesh edit mode section about halfway down the menu and check the «center» checkbox.
• Exit the menu and go to face select mode in the top left corner of the 3D viewport or by pressing 3 on the number row.

If you have detected at least one face with zero area you can follow these steps to find other zero area faces:

• Go to edit mode
• Press 3 on the number row to enter face selection mode
• Select the zero area face you have located
• Press Shift+G and choose area
• Press M and choose «by distance»

Now while we are in face select mode, we will see a dot in the center of each face. If a dot appears on an edge, it means that there is a face present there that doesn’t have any area.

To resolve zero-area faces, select the face, press M to bring up the merge menu and choose by distance.

This will merge selected vertices that occupy the same space and dissolve any geometry dependent on the removed vertices. In this case, our zero-area face.

The most common way we accidently create zero area faces in our mesh is when we use the extrude tool.

The extrude tool is a macro consisting of multiple operations. It will both create geometry and transform this new geometry in one go. When we cancel an extrude operation, the geometry is still created but not moved, leaving geometry behind.

This is not a bug; it is a feature because seasoned modelers usually use this trick as part of a longer chain of tools to create certain shapes. But it is easy for beginners to fall into the trap of thinking that this geometry is deleted if the operation is canceled.

How to deal with unconnected edges, vertices or faces in Blender?

The most common issue here is that we simply have separate parts that are not connected correctly. Often and if there is no gap between the unconnected elements, we can connect edges, vertices or faces by selecting the parts that should be connected with box selection then press M and use «by distance» to merge the disconnected pieces together.

When selecting a vertex, Blender will highlight the connected edges, fading towards the connected vertices. If there is one direction the vertex is not highlighting, it is most likely because there are two vertices sitting on top of each that are not directly connected. It looks like this:

However, if there is a gap between the unconnected parts, it depends on what we want to do. Do we want to add geometry in between the disconnected portions or simply merge one into the other so that the faces share vertices?

If we want to merge the parts, the above solution should do it. If we want to create new geometry in-between, we can use the F key. Simply select one vertex from either side and press F to join the two vertices with an edge.

We can then select the edges that should contain a face and hit F again to create a face. To extend features and understand the F key, you can use the F2 add-on and take a look at this video that explains it’s features.

Just note that when the F2 add on is used incorrectly, it can lead to a few of the problems on this list.

We also cover gaps in the geometry further down in this article.

How to find and delete loose geometry

To get rid of loose geometry follow these steps:

• First enter edit mode,
• Go to Vertex select mode by pressing 1 on the number row.
• Hover each piece of geometry inside your object that you want to keep and press L to select each one.
• Press Ctrl+I to invert the selection. Last press X and delete vertices.

Loose geometry is geometry that is floating around without a connection to any of the main pieces of our objects mesh. Or simply unwanted and unconnected geometry. Most often this geometry is only made up of vertices and edges and won’t render inside your scene. But they can create other problems.

For instance, performance issues and bounding boxes larger than necessary. It can also lead to origin points ending up in the wrong location if we want to set them to the center of the mesh.

How to check for Intersecting and Self-overlapping geometry

Intersecting geometry as equally a feature and a problem. If you are 3D printing something you will need a manifold mesh, meaning, a watertight mesh. No holes or geometry issues. can be present. It needs to be solid and have volume that can be calculated.

So, for 3D printing, intersecting geometry is a problem. There is a built-in add-on for Blender called 3D print toolbox. You can enable it just like any other add-on from the add-on section in the preferences.

After the add-on is enabled, you will find it on the right-hand side tool panel in the 3D viewport in its own tab named «3D print».

The 3D print toolbox isn’t just for those that 3D prints. It can be useful for all artists. For instance, it can help you check if your mesh is manifold. Very useful when simulating things for instance.

For intersecting geometry, the 3D print toolbox has a check feature, helping us to see if there is intersecting geometry. Click the intersections button and Blender will spit out a number telling you how many faces are intersecting. Then click the number to select the intersecting faces.

From there you can choose how you want to deal with the problem and if it is a problem at all.

One way to deal with intersecting geometry is to use a Boolean operation to mold the pieces together.

Faces bending incorrectly

If you have n-gons or quads that aren’t flat, they can have multiple ways of bending. The easiest example is a quad that looks like this. There is only one face in this shape. Blender triangulate it behind the scenes to be able to represent it in 3D space. It can’t bend both ways at the same time.

Then if we move one vertex, the triangulation can change like in this image.

All quads and n-gons need to be triangulated in order to be represented in 3D space. So, Blender does this behind the scenes. Sometimes though, Blender can get it wrong. In those cases, we can either move the shape so that it bends the way we intend it to, but we may not want to distort the shape. In those cases, we have to triangulate it manually.

We can either select the two vertices we want the bend to go across and presss J to join them. That creates an edge and converts the quad into two triangles.

Another alternative is to use the triangulate modifier.

With it, the whole object is triangulated as part of the modifier stack, and we don’t have to deal with the extra geometry in edit mode.

Non-manifold vs manifold meshes

Another phrase for a manifold mesh is a watertight mesh, or one that has volume and doesn’t have holes in the geometry. A non-manifold mesh is therefore a mesh object with holes, no volume or is in some other way an impossible real-world object. Self-intersection parts of the geometry would be another problem making an object non-manifold.

A non-manifold object isn’t necessarily a bad thing. It just means that it isn’t possible to represent the object in the real world, or reproduce it, for instance by 3D printing.

An example of a useful non-manifold object would be a plane. A landscape could be another example. The ground is rarely created manifold in a 3D scene, yet it serves its purpose.

Scenarios where we need to be aware about manifold or non-manifold is when we need to 3D print or when we simulate. Also, Boolean operations work best with manifold objects. Any scenario when we need to calculate something based on the objects volume usually requires a manifold object.

We can check if an object is manifold by using the 3D print toolbox add-on taht comes with Blender. Even if you don’t intend to 3D print, this add-on can be useful.

Enable it just like any other add-on from the preferences add-on section. Once enabled, open the right-hand side tool panel in the 3D viewport by pressing N and find the «3D-Print» tab.

In the clean-up section, you will find a «make manifold» button that will help you solve several potential problems with your mesh object.

How to deal with gaps and holes in the mesh

Sometimes we find ourselves with a hole in our mesh. It can be anything from an uncleaned photoscan or a poorly created mesh. I have also had it happen when sculpting. Sometimes there can be either a problem with the base mesh or it can accidentally happen through some operation.

Either way, there are several ways we can deal with this.

We can try to use the «make manifold» feature that we can find in the 3D print toolbox add-on. Enable it from user preferences and find it in the right-side tool panel in the 3D viewport. Go to the 3D print tab and expand the cleanup section and simply hit «make manifold»

In some cases, we can cover the hole in the mesh manually by simply using a combination of modeling tools. Often this includes new edge/face from verts, often referred to as the fill tool accessed with the F key. Also the join tool accessed with J is common usage when repairing mesh.

But other tools can also be helpful. For instance the grid fill tool.

We can also just fill holes with an n-gon and then tap the mesh with a brush in sculpt mode using dynamic topology. This can help us regenerate the mesh semi-automatically.

The last resort if there are a lot of holes that would be time consuming to repair and that doesn’t get resolved with the make manifold tool could be to let Blender remesh either with the remesh modifier or one of the more recent remesh tools.

Messy topology or varying mesh density

Sometimes an object has a particularly messy topology. It can be an automatically generated object, photoscan or a sculpted object for example. To make a more uniform mesh that is easier to work with. We primarily have two options. Remesh or retopology.

Retopology is the manual way of creating a new topology on top of the old mesh to make it more workable and ready for other parts of the pipeline. For instance, shading and animation.

There are several tools we can use to retopology an object. For instance, using a third-party add-on like the retopoflow add-on. It greatly reduces the time it takes to retopology a model thanks to its smart tools.

Other methods that are built into Blender includes use of the polybuild tool and clever snapping settings.

We can also use remesh to recreate a quad topology.

How to remove internal faces in Blender

To remove internal faces in Blender, follow these steps:

• Press tab to go to edit mode.
• Go to Select->Select all by trait->Interior faces
• Press X and choose Faces.

Preferably you can go to wireframe view by pressing Shift+Z so that you can easily see what is selected before you delete and geometry. Also if you happened to delete the wrong geometry, you can press Ctrl+Z to undo the operation.

Final thoughts

In this article we covered several common mesh and topology issues that we may come across at some point in our 3D modeling career.

Everything from closing gaps to removing internal faces or recalculating normals. All of these are common errors that are often solved multiple times during the modeling workflow. Sometimes it is a result of how we use a tool and sometimes it is the result of not understanding the tools we use properly yet.

Either way, developing a good habit of detecting and solving geometry and topology issues as we go is essential for 3D modelers.

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