Using 3D Meshes in 3D Modeling - Tutorial
Updated: Sep 21, 2020
Let's say you are trying to recreate a model from your favorite game but just looking at pictures is proving more difficult that you imagined. Or you've downloaded a cool .STL file from Thingiverse or MyMiniFactory but you want to make some tweaks.
In this tutorial I will be showing you how to most effectively prepare your 3D meshes and the basics of how to use them when creating your 3D models
For this tutorial I will be using Onshape as my CAD software. It is free and in-browser and has all the tools I need to create complex 3D models. If you are using a different CAD software I'm sure it has similar if not identical tools that you can use to mirror these tutorials.
I will also be using Blender
Lastly, the example for this tutorial will be the Railgun from Halo 4. I got the .OBJ file from the 405th's Armory.
Importing a Mesh
This is what you will see if you import most .STL files or .OBJ files into Onshape
Notice that it a singular mesh. This is not what you want to use for complex models such as this. In actuality this mesh is comprised of over 200 meshes. You can see where they overlap but due to the fact it is currently considered a singular mesh you are unable to view them individually or use the hidden internal vertexes without a lot of arm twisting.
Another disclaimer, while CAD software like FreeCAD have features such as create solid from mesh, this may only work for meshes with a low amount of vertices. Also the solids you get out of this are going to be covered in the vertices and polygons of the original mesh, meaning that you are getting no smooth surfaces. It most likely won't be noticeable in the final print if you are just looking to solidify something and slice it in pieces, however I have found that there is a lot more freedom in design if you create it yourself from scratch. Also in my experience, the create solid from mesh option, usually leaves you with a lot of unsolvable mesh components anyway.
This is why the first thing we are going to do is import this model into Blender. Most likely you will be working with an .STL or an .OBJ, either is fine and will use the same method.
Here is what you should see now that the mesh is imported
Next, select the model, select modeling in the upper tabs, and then in the upper left, select Edit mode from the drop down menu.
Next, you will see several new options appear in the upper left, select Mesh, Seperate, then By Loose Parts
What you should see next, is that potentially hundreds of different meshes appear on the right hand side. If none appear, that means who ever made this mesh did a good job of connecting every single last vertex and you might as well go back to your CAD software and import it as is.
At this point you are just going to want to go ahead and export as an .OBJ file. All the default options in the export menu are fine.
Now when you import it into your CAD software you should see that all the meshes have been separated. This is advantageous as you can now single out meshes and work on them one at a time. You don't have to worry about other meshes blocking reference vertexes and once you are finished you will be able to combine the parts however you see fit to make printing or assembly easier
One last note important note
Once you are at this point, I would highly recommend breaking the meshes into groups of about 50 at the most. Essentially export from this document meshes 1-50, 51-100, etc. and work on making parts from them in separate documents. Trying to make the whole model in single document like this can easily cause you to create several hundred features that can really slow down your CAD software. You can keep them in .OBJ when you export and when you finish them in your secondary document, export them in .sldprt format. In my experience this format has the least amount of issues and will record location information so wen you reimport all the groups of parts they will be in the correct place.
I employed this technique of separating the meshes into groups when I made the SPNKR rocket launcher form Halo, it took me only two days to model all the parts of the rocket launcher as opposed to the 3 weeks it took me to model the Halo Reach Assault Rifle which I failed to break up into multiple meshes or into separate documents. This time discrepancy is largely due to the fact that Onshape ran so much faster when it was remembering info for several hundred features, but maybe just about one hundred at a time.
Basics of working with a 3D Mesh
A bulk of your project will most likely be able to be accomplished with a combination of lofts and extrusions, I will go over briefly how you can use these to get a 3D model out of your meshes, however I have other tutorials that go into more advanced Loft techniques.
For this section I will go back to my SPNKR build. As you can see it's comprised of 110 different meshes. I chose to break this into 5 separate documents. Turned out a lot of meshes were just for decals and textures and were essentially 2d rectangles, these meshes were deleted as they don't actually affect the geometry of the rocket launcher.
Extrusions, Plane, and Use
Here we can see the first 20 meshes that I worked on and its where we will start creating our first 3D parts.
First, we want a plane on which to sketch on. As you will notice you cannot select the "faces" of the mesh nor their edges. The only thing you can utilize on the mesh are the vertices. For this reason there are two major ways of creating a plane.
Three Point and Plane Point
Using Three Point when creating a plane will require you to select three points on the mesh. These three points will define your plane. This method is probably the most versatile and pretty much will always work.
If your desired surface is parallel to another plane or one of the three principal planes, you can also use Plane Point. Plane Point will essentially create a plane parallel to the one you define and move it to the mesh point of your choosing.
Now that you've created a plane, it is time to start sketching. While you can just set your view normal to the sketch plane and start eyeballing things, there is a method that will ensure you have maximum accuracy with respect to the original model.
For this purpose we will use the 'Use' function
Essentially what the 'Use' function does is allows you to select parts, faces, edges, points, etc. and project them onto the sketch plane. In our case we want to project mesh points onto our sketch plane. Here you can see the point I selected and you can see the usable point that is now project onto my sketch.
These reference points can now be used to create your sketch by connecting them with lines, curves, shapes, splines etc. Splines are especially useful when trying to make smooth shapes out of the jagged polygons and triangles of the original mesh. You can see a great example of this in my Halo Reach AR Stock Pad.
For this example I will be projecting three points and using them to define a circle.
Now that I have an enclosed sketch, I want to extrude it to create the rough cylinder shape being used here. Once again, you can extrude "up to vertex", where you can select a mesh vertex to get the perfect length.
Now that I had my rough shape I added two, 'two distances" chamfers to finalize the part
Before and After
As you can see this looks a lot better than the original mesh, and more importantly I can edit this part as I wish.
Now that we've gone over how to extrude basic shapes, we can go one step deeper and talk about Lofts, Lofts can be thought as extruding a sketch that slowly morphs into the end sketch.
For this section we will be switching to another set of meshes from the SPNKR build
Here we have an example of a very simple loft, essentially following similar steps as seen above, we want to create two different planes, with two different sketches. In this case we have a sketch of a circle and a sketch of a singular point. A loft is then use to create a solid part that connects the two.
Before and After
This is where we start to get into some of the more fun and complex geometry and uses for lofts.
Here we can see the front grip of the rocket launcher lofting several different oval shaped sketches. These sketches all required their own plane and were created by "Using" the vertices of the mesh and creating an oval by connecting all the projected points with a closed spline.
Before and After
There are some more advanced techniques using curve projection that I will go over in their own tutorials, but for now I hope that this tutorial helps you progress in your 3D modeling.
Once you are done creating parts using every mesh available you will end up with something like this. I combined some meshes when creating them initially, but still ended up with 67 different parts.
The next step will be to combine these parts and slice them for optimal printing and assembly, but that is for another tutorial.
I hope this tutorial was useful to you and will help you create your favorite props from your favorite media. Next I will be exploring more advanced Lofting techniques while going through the entire prop making process so that you can follow along and hopefully end up with a simple, fun prop of your own
You can find that tutorial here.