Additive Manufacturing Strategies

From NURBS to NURMS: Learn the Basic Terms & Get Your 3D Modeling Act Together  

ST Medical Devices

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UntitledWe all know how important it is to be able to walk the walk in life, but when it comes to the world of technology, this is one area where perhaps talking the talk is more important; after all, learning, explaining, and problem-solving are all a whole lot easier when we are on the same page. The problem is that a dictionary for 3D modeling jargon hasn’t really been written yet, so you might sometimes find yourself scratching your head in confusion in regards to what something means.

i.materialise is about helping, not leaving us in the dark to look completely idiotic, so they’ve prepared a list of the most common terminology you might want to be in the know about regarding 3D modeling. The most important thing to learn about, of course, as a complete novice—is the 3D model. Not to be confused with a 3D print (and the terms are often used interchangeably), the model is what you create digitally, from within your modeling software. This is the beginning of 3D printing altogether, as you put together the design that will ultimately be converted to an .stl file and printed.

And while this isn’t the most glamorous jargon, if you commit some of this to memory when embarking on your journey to becoming a master maker, life will much more enjoyable—and your ‘models’ might just come out that much better. So, let’s begin!

NURBS-curve

Control Vertices

Non-Uniform Rational Basis Spline, or NURBS, modeling is a process used to make both curves and surfaces, and is mathematical type of technique that will allow you the accuracy you seek. Curves are made with a tool like you might summon up from Paint or Adobe Illustrator, somewhat like a pen, and allowing you to draw in 3D space. If you need to edit it, control vertices (CVs) are used like handles.

“Alternately, a curved surface can be created by revolving a profile curve around a central axis,” states Fabian from the i.materialise team in the blog. “This is a common (and very fast) modeling technique for objects that are radial in nature. That is why this modeling approach is very popular for creating automotive and industrial parts.”

rhino-NURBS-3d-modeling

A NURBS model created in Rhino by the i.materialise team.

If you are interested in making polygon models, i.materialise suggests comparing them with NURBS models first, because you will see that they are mathematical. The polygon model is also known as a mesh, and definition of the model is made up of:

Vertex/Vertices – Very simply put, the vertex is just a point in 3D space which allows you to create a polygon by connecting with edges, and then moved around to make a shape.

Edges – Also part of the polygon, these make up the the shape of the model, but can also be used to transform it. An edge is defined by two vertices at their end points. The edges of a single polygon are pictured in red in the image below.

Faces – This is the most elementary part of your 3D polygon. After three or more edges are connected together the ‘face’ is what fills in the empty space between the edges. It also makes up what is visible on the polygon mesh.

polygon-face-edge-vertex (1)

The face is depicted in green, edges in red.

These are the elements that will allow you to edit and change the shape of your 3D model—and here lies one of the greatest benefits of design and 3D printing, in that you can keep changing and tweaking different portions of the model as long as you like, without expense or having to have someone else do it for you. In this case, if you change any of the vertices, you alter the 3D model’s shape.

So with all these straight edges in play, exactly how do we make curves and round edges? The answer is in subdivision surfaces, or Non-Uniform Rational Mesh Smooth (NURMS), which can be used for smoothing pixelated meshes.

“Subdivision surfaces use an algorithm to take polygon geometry and smooth it automatically,” explains Fabian. “They actually subdivide each polygonal face into smaller faces that better approximate the smooth surface.”

You will find that with NURMS you are able to achieve much greater detail. See the image below as it displays the chess piece with much smoother surfaces. This is just a beginning in tech terminology, but should lend a great start for 3D modeling.

See how much smoother the chess piece is, thanks to the NURMS modeling technique.

See how much smoother the chess piece is, thanks to the NURMS modeling technique.

Be sure to see i.materialise for a list of tutorials that you should find very helpful for 3D modeling and printing, as well as overviews on modeling software or more about 3D printing and materials. Were these terms helpful? Discuss further in the i.materialise 3D Modeling Terms forum over at 3DPB.com.

[Source: i.materialise]

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