3D Modeling, CAD, and You

Basic Coverage:

There are two ways to make a model. Parametric 3D modeling is done by using parameters to define a 3D model. Used for engineering, this allows precise calculations and dimensions to be stored. For example, a circle would probably be stored as the equation for a circle + a radius parameter.

Mesh 3D modeling is done by directly manipulating the computer mesh representation of an object. Objects are discretized into points that make up polygons (triangles and quadrilaterals). For example, a circle would be stored as a collection of points and line segments that approximate the shape of a circle.

A good analogy is vector vs raster format for photos and images.

Fusion360 actually combines the two into a single software.

3D printing utilizes STLs, which are a mesh based file format. There are two ways to fix resolution - before an STL is exported, increase the polygon count. (Blender - subdivision surface modifier, Fusion360 - export settings). Or, import a STEP file into your 3D printing slicing software, which then does the conversion automatically into a mesh format with better approximations for things like curved surfaces.

Universal Terminology:

• Mesh

• Body

• Feature?

File formats:

• .STEP

• .STL

• .SLDPRT

A note on Piracy

STL piracy primarily happens over Telegram groups, such as "STL Forest" and other groups hyperlinked to that group for different purposes. Notable anti-piracy observations - you can't find files for EVERY creator, it's difficult to find if the filename is generic or doesn't include the creator's name in it, and it's difficult to find files if the creator's name is generic (There's a studio accurate X-Wing model by a person with a super generic name that I couldn't find the model for).

“We think there is a fundamental misconception about piracy. Piracy is almost always a service problem and not a pricing problem,” he said. “If a pirate offers a product anywhere in the world, 24 x 7, purchasable from the convenience of your personal computer, and the legal provider says the product is region-locked, will come to your country 3 months after the US release, and can only be purchased at a brick and mortar store, then the pirate’s service is more valuable.”

The proof is in the proverbial pudding. “Prior to entering the Russian market, we were told that Russia was a waste of time because everyone would pirate our products. Russia is now about to become [Steam’s] largest market in Europe,” Newell said.

The purpose of Steam is to provide as much value not only to the customer but also to other game publishers. “Our success comes from making sure that both customers and partners (e.g. Activision, Take 2, Ubisoft…) feel like they get a lot of value from those services, and that they can trust us not to take advantage of the relationship that we have with them.”

- Gabe Newell, Steam

Fusion 360 Notes

Mesh to Body Conversion: Fusion can convert mesh formats into bodies. There are two options - where it turns the mesh directly into a body, keeping all of the thousands of triangles as individual faces, or it attempts to interpret the mesh (for example, all co-planar triangles == one flat square surface_. This is the "Prismatic" setting, and it's locked behind the paywall. Yay.

Fusion is based on a top down assembly design philosophy. 

https://productdesignonline.com/tips-and-tricks/understanding-bodies-and-components-fusion-360-rule-1/#images-1

Reasons that I'm using Solidworks instead of Fusion
(aka, logical reason to not use Fusion that aren't rooted in "I don't like new things")

1. Bottom up design reflects manufacturing intent. The process of designing a part more closely mirrors how the part will actually be made in the feature tree vs. solid bodies.

Things I was mad about at first, but figured out the Fusion equivalent for:

1. Mates - these are just called "joints"

2. Assemblies - they exist, they're just called "components" and placed within "components"

3. Views - they work differently. What I care about is spatial manipulation of assemblies to move things around, take a look inside, look at it from top/bottom/left/right/front/back/normal to a selected surface, and just generally "spin CAD".

   1. Fusion shortcut for 4 simultaneous views is SHIFT+1. You can have 4 simultaneous views. This is ok for having views without having to constantly reset them, but still bad for "spatial manipulation".

      1. I don't see a "Normal To" view shortcut.

Things I don't know yet:

1. Solidworks feature tree vs. Fusion timeline. 

   1. Actually they're the exact same, just portrait vs landscape.

2. Links - Components in a component assembly can easily have linked dependencies on other components (creating a body on the plane surface of a different component). Within the assembly it's fine, but removing it from the assembly to use somewhere else might cause problems?

   1. Side note - lets say you replace a component that has dependencies with other components. You will need to insert the new component, and manually step through the process to find all the dependencies and redimension them. https://www.youtube.com/watch?v=rl4G6ph97tU
      Conclusion? Don't use dependencies regardless of CAD software. It will break everything.

3. How they handle STL mesh to Body conversions.

Why STL over STEP?

1. Control over resolution quality export. All slicers use the same algorithm to convert a STEP to STL, and it's not as good, creating much larger meshes than exporting from CAD.

2. Quality control. I imported a STEP once that, after separating the STEP into 3 objects, had an unresolvable error of "first layer does not exist" on one of the parts for no reason. STL will always work because it's the intended input before GCode is generated.