How to model arch moldings in Blender 2.8X


Assalamu’alaikum. Hi guys.

My name is Widhi Muttaqien from Expose Academy.

In this tutorial video, I want to show you my approach in modeling arch moldings. The type of arch moldings that I’ll be covering here are not the straight type, but the type that turn to another plane. Besides buildings, you often see this kind of profile on classic style furniture, such as cabinets, wardrobes, clocks, etc. So I believe this is an essential skill to master especially if you are doing a lot of classic style architectural or interior design works.

I hope this short tutorial can be helpful. Happy Blending!

Regards, Widhi Muttaqien

Video transcript

Assalamualaikum. My name is Widhi Muttaqien from Expose Academy. In this tutorial video, I’m going to show you how to model a classic style arch molding like this one inside Blender 2.8 or above. There are many types of moldings or decorative details in architecture. We’re going to focus or arches now. But not just arches like these. This type of arches is fairly easy to model inside 3D. If you followed my channel, you might already learn how to create simple crown moldings from my earlier tutorial. Basically, you can use the same method for these types of molding in Blender. You just need to rotate the result. And that’s it.

The more challenging type of molding is this kind of architectural profile. The biggest problem is this cornering part. If you only have the profile going down, basically we can create a 2D curve that is oriented to that direction, let’s say the Y-axis direction. Again, we can just use the previous crown molding technique for this scenario. But because the profile is turning to another direction. This is like having multiple orientations in a single curve path. So this part is facing the Y-axis, while this part is facing the Z-axis. Besides buildings, you often see this kind of profile also on classic style furniture. Such as cabinets, wardrobes, clocks, etc. So I believe this is an essential skill to master especially if you are doing a lot of classic style architectural or interior design works.

The problem with pure 2D or 3D curve

Now, you might be thinking, why not just use a 3D curve then? Well, there are many limitations with the 3D curve in Blender. Let me just show you what I mean. Here I have a 3D curve that follows a path just like the molding we want to create. I also created a profile curve for the bevel. If I select this curve, you can see that this curve is a 3D type curve. Now, if I go to the bevel parameter and pick the profile object. It produces this tilted result. Also if we look at it from above. On straight segments like these, the result looks good. But on corner areas, or when it turns, the profile thickness gets smaller. All of these problems happen due to the twisting mechanism in 3D curves. You can try different twisting methods here. But as you can see, none of them really fix the problem out of the box.

Okay, now some of you might be asking again, so what’s wrong with using the 2D curve then? Well, as the name implies, the 2D curve is 2D. It does not support Z-axis as the coordinate for their vertices. If we convert the curve to 2D here, it will be flattened out. Yes, there is no twisting problem on 2D curves, that is why the resulting profile looks good and consistent. But we lost the vertical arch shape here. It becomes flat like the rest.

Let me undo this, so we have our 3D curve again. One way to create a nice arch molding is to use the 3D curve like this. Convert it into a mesh. And then just fix the tilting problems manually by extruding here to here. Then here to here. Then cut them using the knife tool, and so on. But trust me, this method just takes too much time and effort. So my solution is not to use a 2D or 3D curve, but combining both in a single workflow.

The workflow

Just for a quick overview of the workflow. First, you need to create 3 curves. One for the bevel profile which is a 2D curve. Another curve for the flat or horizontal path, which should be a 2D curve type also. And finally the last curve for the circular path, which is supposed to be a 3D curve. We use these curves to create the bevel. Then after that, we convert the 2 path curves into meshes again. In the mesh modeling session, we use the “intersect knife” command to split them apart. And then the final step is fixing the resulting mesh as needed. Such as patching holes, fixing flipped normals, adding smooth shading, adding volume, etc.

Let’s see this workflow in action. First, make sure you have the 3D cursor at the center. You can press Shift + C to do that. Now, for creating the curves you can directly use the curve objects available in the extra object curve addon. But I will assume you don’t have the addon active, so I will use simple mesh objects for now and then later convert them into curves. Press Shift + A, “mesh”, and create a plane object. We will use this plane object for the flat or the horizontal path curve. Next, we need a circle. Press Shift + A again, “mesh”, and choose “circle” here. For this circle, we need a lot more segments so that the resulting arch model looks smooth. Let’s input 64. And for the radius, let’s make this smaller around 80 cm. Next, let’s rotate the circle so it is standing straight. We can press R, then X and then type in 90. We need to snap this circle so it is aligned to this vertex. To do that make sure the snap setting is in the vertex mode, and this is set to “closest”. For the rest, just use the defaults. Move this to the front while holding the Ctrl key and move the mouse cursor to the vertex location that we want to target. And let’s just bring this down a little.

Now, when doing this workflow, you need to carefully pay attention to the local Z-axis. If you have the transformation orientation mode set to global. You can not tell the difference because they all look like pointing up. But if you set this to local, we can see that this circle’s local Z-axis is pointing to the front. It should be pointing up like the plane object. To fix this we can apply the transformation. So press Ctrl + A and then choose “rotation” here. Now we have this local Z-axis pointing up just like the plane object.

Next, we need to create the curve for the bevel profile. When creating profile objects, I usually like to think that it is aligned with the left side of the path object, and not the right side of it. This usually works best for a closed 2D curve. But not best for 3D curves. But don’t worry we can still flip the profile easily using the switch direction method on 3D curves. Let’s go to the top view. We want to create the profile at roughly 20 cm by 20 cm size. So about these 4 grid squares here. Shift right-click here to move the 3D cursor to this location. Shift + A, “mesh”, and I’m going to create a single vertex. A side note here, you need to have the extra object addon active to use this single vertex object. If you want to create the vertex from a plane object, I already show this method in the previous crown molding tutorial. Okay. Now we have a vertex here and we also automatically brought into the edit mode. But we won’t be able to see the vertex unless we are in the vertex mode. Press E, then X and place the new vertex here. Press E again and place it here. And again. Next, I want to use the free-form method of vertex extrusion. For this, it is better to be in the tweak mode. You can press W several times to access the tweak mode. Until you can see this tweak icon here. Okay. Now, hold Ctrl and then right-click on the location you want to create the vertex. Just keep doing this until you have the profile shape that you like. Now to align this vertex to the top vertex. We can press G, then X and then hold Ctrl and click on this top vertex. Okay. I think I want to tweak these vertices to make it look nicer. Okay. Now, if you only do a flat horizontal crown molding. You want to connect these vertices by pressing F. But the thing is with our workflow. We will use a mesh modeling command called “intersect knife”. And this command doesn’t work well if we have too much face interference. Or in other words, multiple faces that exist in the same exact location. So let’s select this vertex. Basically, we want to remove this vertex. So press X and then choose vertices. It is okay to have an open profile like this, because Blender will use the origin of this object as the reference to place it in the path curve. Even if we don’t have any vertex at the origin location. Yes, this will generate a bevel profile without any volume. But we’re going to add the volume later afterward in the mesh modeling session.

Let’s go back to the object mode. Before we move on. I want to stress out that it is important for the profile object to have the local Z-axis pointing perpendicular to the profile plane. That is why it is safer to create the profile from the top view, instead of the front view. This is so the local Z-axis will be pointing up without the need for any additional step. Okay. Next, select all of these objects. And convert them to curves by going to the object menu, “convert to”, and then choose “curve” here. For the profile curve, just set this as a 2D curve. For the rectangle also, set this to a 2D curve. But for the circle, just leave it as a 3D curve. Okay.

To create the bevel, select the rectangle curve first. In the geometry section, you will find the bevel parameters. Use the eyedropper tool here to pick the profile curve. Now we have something like this. Next, let’s do this also for the circle curve. Besides using the eyedropper, we can just click here to select the profile object from the list. The profile name is “vert” so just select this. So now, we have something like this. We can see the profile is facing at the wrong direction. To flip it, we can press Tab to enter the edit mode. And make sure one of the vertices is selected. Then in the “segments” menu, click this “switch direction” command. Go back to the object mode. Now we have all the bevel geometries that we need. But, before we convert these back to mesh objects, let’s duplicate them first, just to be safe.

Mesh editing session

Let’s convert these 2 objects into meshes. Make sure both of them are selected. Go to the object menu. Then choose “convert to”, then “mesh”. Then press Ctrl + J to join them together. We now have a single mesh. To make the profile shape flow nicely from the rectangle to the circle and back, we need to cut the mesh in these intersection areas. To do that we can go inside the edit mode. I’m using the face mode now. Select all by pressing A. Then in the “face” menu. You can find the “intersect knife” command. Click on it. And then in the operation parameters panel, in the surface type, choose “self intersect”. Then in the separate mode choose “all”. This is so we can easily select the parts that we don’t need and to remove them. Make sure nothing is selected. Hover on this part and then press L on the keyboard. And then hover to this part and then press L also. Essentially we only select the parts that we need. Press Ctrl + I to invert the selection. Then press X and choose “faces”. Now we have something like this.

Honestly, I didn’t expect the result to be this tidy. I usually get some minor holes in the intersection area. Basically, after the “intersect knife” process you need to fix the holes or the topology in this area. I was about to show you that, but, surprisingly this already looks nice. But let’s make it more perfect. Press A to select all. Then press Alt + M and then choose “by distance”. This will merge all vertices that are close together. Next, we can merge this vertex to this vertex. To do that make sure both vertices are selected. But the upper one should be the last one selected. Then Alt + M again, and then choose “at last”. We can do this with the other vertices. Select this one. Hold Shift and then this one. Alt + M and choose “the last” or just press L. And this is the last one. Alt + M again, then L. Okay.

Next, let’s fix the smooth shading. If we want the intersection line to look sharp when we later apply the smooth shading. We can select this vertex. Then hold Ctrl and then select this vertex. Press 2 to go to the edge mode. Right-click, and then choose “mark sharp”. Now we can go back to the object mode. Right-click and choose “shade smooth”. Let me turn off the wireframe display. And then turn on the “auto smooth”. We can see the intersection line here looks sharp. For the left side, we can add a mirror modifier later. For now, let’s add some volume to our molding object. To do that, select this edge here. Then this edge. And also this edge. Next, we want to extrude this up on the Z-axis. So press E then Z, and then hold Ctrl and click on this vertex to snap the extrusion height. Next, we can select this edge and then this edge. And then press F to create a face between them. We can do this also with the other edges. Press F. And this one and then this one. Press F also.

Now for the circular part. We need to make way for the extrusion. So go to vertex mode. Select this vertex and move this on the X-axis. To extrude the upper part. Let’s go to the edge mode. We don’t need to select the whole edges from end to end. Just select this edge. Hold Ctrl and then select this edge. Then press E to extrude, then press Y, and then while holding Ctrl, click on this vertex to snap to it. Next, select this edge and then this edge, then press F. Then this edge, with this edge. Press F again. Go to vertex mode. We want to merge this to here. So hold Shift and click this vertex. Alt + M, and choose “at last”. For this hole, we can hold Alt and click on any of the edges around the hole. Then press F. If you want to go further you can create edges that way using the J shortcut or the knife tool. But I will just leave this as is. For this large hole. We can also use the same method. Hold Alt and click on any of the edges here, then press F. Personally I think this is good enough as mostly no one will ever see this side of the model. But if you want to go further. You can convert the vertex selection to edge selection first. You will understand later why you should use the edge mode. Go to the face menu and choose “grid fill” here. As you can see, Blender can create this nice quad based fill using the “grid fill” command. But I found this command works well in the edge mode. That is why we switched to the edge mode before performing the “grid fill”. The last step is adding the mirror modifier. Make sure we use the X-axis and turn on the bisect option here to prevent double meshes on the model. And that’s it, we now have a nice arch molding 3d model.