3D Printing, also known as Additive Manufacturing, is a method of remodeling your digital 3D objects in the real world using dedicated technologies. There are numerous 3D printing technologies out there such as Stereolithography (SLA), Selective Laser Sintering (SLS), and Fuse Depositing Modelling (FDM) just to name a few.
Each technology comes with its own set of pros and cons, however, they all share a common denominator: 3D printers are generally picky about what can and cannot be printed. While 3D printing brings about a lot of enthusiasm, it is definitely not a cheap process. Most 3D printing services charge you by volume (cubic centimeters), which means it’s in your best financial interest to make sure your model prints as a hollow figure and not as a solid one. Your model will not print hollow by default. Hence, comes the importance of knowing the dos and don’ts to help you make better choices.
This documentation will explain the common issues you will run into when submitting your 3D models to your 3D printing service provider.
###Thickness###
Clara.io has a great solution for adding thickness to your model and making it ready for 3D printing. Select your model and then click on the Add Operator drop down menu. From there, select Thickness and adjust the Length parameter. However, there are some key factors that you should keep in mind before submitting your final product.
Note that each service provider has their own requirements for a minimum shell and wall thickness. For example, one service may have minimum requirements of 0.25 mm, others 1.5 mm wall thickness. Be sure to check the minimum requirement first with your service provider. Excessively thin walls (like paper thickness) are impossible to print.
Thin or small models are often less durable and vulnerable to breaking. This is especially a concern when they’re connected to large mass models which can cause them to break off during printing or shipment. That’s why you always want to keep an eye on the thickness of your geometry’s walls. If your object’s units are measured in meters or feet, the thickness of the walls may be fine. However, when you scale them down to inches and centimeters, the thickness of the walls may become too thin. So you need to make sure the size of your shell or walls still meet the minimum requirements of your service provider.
It is possible to print hollow parts, interconnected parts, moving pieces, as well as highly detailed geometries. All models need to be a single piece of mesh unless you intend to glue the pieces together after printing. If you intend to print moving models, make sure there is enough space between moving parts such as gears, chains, limbs …etc.
###Watertight Model###
The term Watertight is used to describe a 3D mesh that is suitable for 3D printing. This means it has no holes, intersecting faces, cracks or missing features. It is important to create watertight meshes so that it is clear to the 3D printer what is inside (if it is hollow or a solid piece) and what is outside. Achieving this process can take many hours especially if the original model was not built with 3D printing in mind.
Although your model appears hollow during the modelling stage in your 3D software, when printing it will be interpreted into a solid piece unless you prepare it otherwise.
Also, it is also recommended that you create a gap at the bottom of your mesh to remove any excess material.
###Non-Manifold Model###
The term non-manifold is used to describe a duplicate edge that easily goes unnoticed. The result is essentially two identical pieces of geometry that seamlessly overlap on top of one another. This is a common mistake among novice 3D artists which results in models not printing correctly. If you duplicated your edges and decided to undo your actions, just remember to undo them twice so that the duplicated edges no longer exist.
Although edge extrusions are not the only cause of non-manifold geometries, they are however the most common cause. Another cause merging two duplicate geometries as one object, which would result in two identical geometries overlapping one another. This only confuses your 3d printer and causes problems with your printed result.
###Inverted Faces###
Inverted Normals and Faces can also be an issue when it comes to 3D printing. The easiest way around this is to turn on the visibility of your geometry’s Normals. If they’re pointing outwards then you’re in good hands. If a Face’s Normals are pointing inwards, simply select the face and apply Flip Normals.
###Formats###
Once you’re happy with your model, you can export it into various formats and have it submitted to your 3D printing service provider. The most common file formats are .STL, .OBJ, and Collada. It is best to find out from your service provider what formats they accept.