Physical models are useful in Architecture, Engineering and Construction industries and can easily be used to visualize different parts of a building design such as artistic facades, crowded equipment rooms, etc. They are useful when coordinating different disciplines during the design phase and when presenting a design to a client. However, they are typically expensive and time-consuming to make, which doesn’t work well for industries driven by construction deadlines. With 3D printing, these expense and time concerns are eliminated.

3D printing is much faster than the traditional method of hand-making models and has become inexpensive over the last few years. This has created new opportunities to accelerate delivery and eliminate risks for design firms. Since this method is faster and inexpensive, multiple models can be made at different times in the project lifecycle. This means models can be leveraged throughout the process, not just at the end of the project. Models can even be created for each design option of applicable projects.

How Do I 3D Print My Model?

To keep it simple for this example, I will use a Revit model and the STL Exporter add-in for Revit, but the workflow should be very similar for other software.

It’s a common misconception that 3D printing is as simple as sending the file to the printer and pushing the print button. Maybe one day it will be that simple, but it is a little more complex.

First, we need prepare the model. 3D printing software, known as a slicer, requires the object to be “water-tight.” This means that everything must to be a solid object. In Revit, each element is modeled as its own “water-tight” mass, therefore, if you try to print a Revit file without preparing it, the printer will print each individual element. This would most likely result in a blob of filament due to the scale of the model and the amount of support structure required and/or elements not printing at all. So, the best way to make a single “water-tight” model is to create an in-place component following the massing of your building. When doing this, try to use simple extrusions, sweeps, voids and blends, as it will make joining the elements and creating a truly “water-tight” object a lot easier. If necessary, conceptual masses will also work for some of the more complex geometry.

Single In-place component following building geometry

Once the model is “water-tight,” the next step is to export the model to a file format the slicer can understand. Generally, models for 3D printing are exported as STL files since most slicers import that file type. This is the format I use for this example. The specific workflow to export a model as an STL file varies depending on the software used to create your model. In Revit, exports are dependent on the active view. Therefore, a dedicated 3D view for the STL export will need to be made and prepared.

Creating a Dedicated 3D View

Create a new 3D view and use the Visibility/Graphics Override to turn off all Annotation categories and any other elements you do not want to include in the 3D printed model. Even though you’ve created a solid component following the massing of your building, it is important to leave the Revit elements activated because much of the exterior detail from these elements will print adhered to the solid component. Once the view is ready and all of the elements you wish to print are visible, you can export the model to an STL. For Revit, this requires the use of the STL Exporter add-in. It is a simple and free tool available from Autodesk. All you have to do is open the STL Exporter, modify the settings as desired and click save.

Slicing the STL File

The final step before sending the file to your printer is to “slice” the STL file. Slicing is the process of importing the printing file into 3D printing software (the slicer) and using it to write the instructions for the 3D printer to follow. The slicer software takes the STL file and various settings you apply and writes a gcode file the printer can understand. The gcode is a set of instructions informing the various motors how to move, what temperature the heater should maintain, etc. to create the 3D model. The slicer software also allows you to preview the print so you can check for different issues at each individual layer.

Slicing models for 3D printing is a huge and in-depth topic that won’t be discussed, however, here are some general things to keep in mind when slicing.

3D printing filament comes in many different colors and material types that require different printing temperatures. These are usually labeled on the filament.

Generally, the smaller your layer height, the better resolution your model will be in. However, decreasing the layer height will increase the print time.

3D printed models are printed layer by layer and therefore anything that overhangs too much will need to be held up by 3D printed supports. The slicer can generate these for you and will be fairly easy to remove from the completed print, but it does require some time to clean up the model post-print.

3D printed models are printed as a single object made up of an exterior wall around the model, which infill takes up the space inside. The wall thickness and infill percentage dictate the strength of your model. A low wall thickness and infill percentage prints quickly but results in a flimsier model, while increasing these settings increases print time but also makes a stronger print.

In order for a print to be successful, each layer needs to adhere to the layer before it. The first layer needs to stick to the printing surface securely as it is the foundation for the entire print. In your slicer, there will be a few different options for Build Plate Adhesion. For models with large flat bottoms, I typically like to use a Brim to help secure the print to the printing surface and keep it from lifting up as it prints.

The scale of your model can also be adjusted in the slicer. (When exporting from Revit with the setting “Use Internal : Feet” via the STL Exporter add-in, scaling the model by 0.6 gives you a print scale of 1” = 40’, scaling by 0.7 gives a print scale of 1”=30’, etc.)

Printing Your Model

Finally, it is time to print your model. Send your .gcode file to your printer and start the print. If your print comes out as desired, congratulations! If not, do not be discouraged. There are many reasons why a print might fail, some of them are caused by issues with either the model or the slicer settings, but a lot of them are results of imperfect 3D printing technology. Prints can fail due to issues with the export from the slicer to the gcode, which simply requires re-slicing your model. They can also fail due to things like layers shifting, layers not adhering to the print bed or each other, filament getting tangled, etc.

Troubleshooting your 3D printer is another topic that requires an in-depth discussion, as it can vary greatly depending on your specific printer, environment and model. With that being said, there is plenty of reliable information available online that can lead you in the right direction. Sometimes these things can happen due to 3D printers being inconsistent, and the only fix is to run the print again. Just be aware, don’t give up and know it might take a few tries to get something to print correctly.

Conclusion

3D printing can be a fantastic method to quickly create cost-effective models, despite issues that require you to spend more time adjusting and reprinting. Currently, it’s not as simple as pushing the print button, but with a little time to prepare the digital model, you can create quick, attractive and inexpensive physical models.

For more information on other Autodesk products, please visit our Autodesk Products page.

Follow ATG on LinkedIn, Facebook, Twitter and YouTube for 24/7 access to top-notch technical content.

This blog is written by Sr. MEP Technical Specialist Colton Haney. If you have any questions or need help with your Revit or 3D printing needs, please email us at whyATG@atgusa.com.