How to prepare a CAD model for 3D printing in Blender

When I first tried to 3D print a CAD model, I made the mistake of sending the file ‘as is’ to a local 3D printing service. They sent it back to me and I didn’t really understand what was wrong with it. I mean, it looked fine on my computer. Worse, the file was a 3D reconstruction model out of several photos I took, which means it was probably full of holes and no 3D printer could work its magic on it. Months passed and I got better at it. If you are a complete newbie at this whole 3D printing stuff, this tutorial may save you the headaches I had while learning how to prepare a CAD model for 3D printing.

CAD models come in many formats and they can be created in many different types of software. For a complete list, check out this Wikipedia article.  While in engineering school and later on my first engineering job, I learned CAD by trying out Catia and Solidworks tutorials. Needless to say, it never caught on with me. It felt too mechanical and stiff to try new ideas. It was all a trial-and-error process. That was until I found Blender. Its open-source philosophy and its easiness for modeling organic forms was just what I needed. Blender can have a steep learning curve because you have to rely on many shortcuts or hotkeys, but once you learn them, you can do a lot of interesting stuff with it. And coming back to the topic here, Blender has a toolbox that greatly simplifies 3D printing final steps.

CAD models come in many formats. Most 3D printing services will display the type of format they want you to upload on their websites. I mostly use .stl files. For this tutorial, you can download my first model that I 3D printed: a flower vase.

Here are the steps to make sure any CAD file is 3D printable.

Step 1

Download Blender. It is available for Linux (my favorite!), Windows and Mac OSX. Install it and get back to read step 2.

Step 2

Once you open Blender, a default cube will be visible. You can delete it by typing X. Import your file (File/Import/STL files) and save it as .blend (File/Save) while you work on it.

defaultcube

Step 3

Make sure the add-on 3D Print Toolbox is active. Go to File/User preferences/Addons and check whether the tool is enabled. If it’s not, type ‘print’ and the 3D Print Toolbox should be enabled as you see below. Don’t forget to save the new setting before moving on.

screen1-3d-print-toolbox

You’ll now have the Print3D toolbox active by scrolling in the left part of the screen (activate the ToolShelf by typing T if necessary).

screen-3d-print-active-path4197

Step 4

No matter which 3D printer type you’ll use, the 3D model must be manifold. This is a fancy way of saying the surface is all closed. Just imagine that you’d fill that closed shape with water. If it leaks, it’s not manifold.

Here is an easy way to check that in Blender: click on Solid in the Print3D Toolbox. The output that you wanna get is made of:
Non Manifold Edge: 0
Bad Contig. Edges: 0

If you don’t get this result, your mesh is not manifold.

For illustration purposes, I deleted a face from the mesh below. By clicking on Solid in the Print3D Toolbox, I get a non-zero number of manifold edges and by clicking on the error, the missing parts are highlighted. Depending on the complexity of the mesh, you can correct these holes by adding or subtracting vertices, edges or faces. You can use the F hotkey to add edges or faces depending on your selection mode (vertex or edge).

screen-non-manifold-edges-path

To edit a mesh, you have to get out of Object mode and into Edit mode.
Once in edit mode, you can pick one of the following selection modes: vertex, edge or face. You can’t add/delete edges if you are in vertex selection mode and vice versa.

screen-editing-mode-path4265

 

Step 5

The next thing you need to have in mind is minimum thickness. In other words, the walls of your mesh must be at least equal if not larger than the minimum thickness of the layer deposited by the 3D printer you’ll use. Any 3D printing service will mention the printer’s resolution on their website – if they don’t, ask.
You can check this by entering the desired value in the text box on the right side of Thickness in the Print3D Toolbox. Be careful about units here as Blender uses 3 types of units: Blender units, Imperial and Metric. If necessary, you can modify this setting on the right side of the screen by going to Scene/Units as you see below. Most of the time though, I just work on Blender units and I select the metric unit when I upload the model on the 3D printing service websites.
So after entering the desired value, click on Thickness. If everything is OK with your mesh, you should get the following output:
Thin Faces:0

If not, the add-on will show you exactly which faces you need to correct as you see below.

screen-thin-faces-path9340

 

You can modify the wall thickness in several ways:
-select all faces by pressing Ctrl-F, select Solidify and on the left side of the screen enter the desired thickness
-scale the whole mesh by pressing on Alt-S with even thickness turned on
-as a last resort, you can manually correct the wall size by moving edges and faces around

screen-solidify-path8721

Step 6

Depending on the 3D printer type you’ll use, now comes the fun part.

Basically, there are two ways of using materials to 3D print:
-melting solid materials which are then extruded as layers, the latter hardening at room temperature. A related method implies cutting sheets of solid material and laminating them together.
-curing liquid materials or binding powders
Within the first category, you may need to add support structures or at least change the orientation of the piece before printing it if your mesh contains overhangs. Support structures need to be removed or dissolved after printing the model.

But this is not necessary for the second category as the surrounding liquid or powder material forms the structure itself.
You can set the maximum angle for overhangs in the Print3D Toolbox, the default being at 45 degrees.

For more options, you can check the documentation of this addon here.

Step 7

A fast way to repair your mesh is to use the Cleanup options from the Print3D Toolbox:
– isolated which deletes isolated vertices, edges or faces
– distorted which smooths down or tesselates faces connected by an angle larger than the one you set here (by default it’s 45 degrees). This will increase the number of faces your mesh will have, which will increase the size of your file.

Step 8

Finally, check on the model’s volume before sending it to the printer. The lower this number, the more you’ll save on material costs.

You can decrease a model’s volume in several ways:
-scaling it by using Alt-S to the desired size
-scaling it to the desired volume by using the Print3D Toolbox option
-removing internal geometry of the mesh while taking care of keeping it manifold in the end

That should be it. Now your model is ready for 3D printing. If you have any questions, please leave a comment below!

For the time being, I don’t own a 3D printer at home and neither do I plan to. I value my open space. But I also care about printing locally and the most efficient way I found to do just that is to enter the zipcode on 3dhubs.com , upload the model(s), choose a material and a 3D hub from the available ones and you’ll get a price estimate for each of them. If you like what you see, you can order the print and have it shipped to your place or pick it yourself. This website saved me a lot of time and money on shipping costs by printing locally without having to go through several options as they were all in one place.

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