Can't extrude sketches in a derived part

[revyakin]

Hi all,

I am working on a part in which some solids and surfaces were derived from a mesh object. I downloaded the object from GrabCad as an .obj file.  It's a relatively complex mesh (a model of a ski boot, I can't to create complex shapes like this). Now I am trying to sketch a ski binding around it by placing planes, creating sketches, extruding them, etc.  I found that I cannot seem to extrude sketches (e.g. created on planes offset from XY, YZ, and XZ planes). As a test,  as soon as I delete mesh-derived solids and surfaces extrusions start to work as always. In the example, I am trying to extrude circles into cylindrical solids. 

The derived component file is relatively large (45 Mb, I apologise). May I ask for hints how to solve this?

Thank you in advance!

[johnsonshiue]

Hi! Inventor has very limited mesh handling workflows. I don't believe what you are trying to do can be done in Inventor easily. It is because Inventor is precise modeler (geometry measurably accurate up to 10E-5 mm). The mesh data is imprecise. Inventor is not good at working with such data.

I think you will be better off using mesh modeler like MeshMixer or Netfabb.

Many thanks!

[revyakin]

Hi Johnson,

Thank you for your note. Technically, I have converted the meshes to solids and surfaces using the AutodeskMeshEnabler tool. Is there a threshold value of (original) mesh complexity or the minimal available RAM?

[johnsonshiue · Accepted solution]

Hi! Not really there is a threshold. The issue is not about capacity. The issue is that such geometry isn't what Inventor was designed to tackle.

Inventor is a precise modeler (3D true-scaled feature-based parametric solid modeler). The objective of using this kind of tool is to create a precise 3D model (up to 0.00001mm) as the ideal build to compare with the actual build.

It is not good at imprecise modeling. Mesh, on the other hand, is not precise. Not every point is measurable. Each mesh element does not represent any design intent. Only the entire mesh model represents the object.

MeshEnabler converts mesh element to a triangular face. This workflow works only if the amount of mesh is limited and the mesh face is relatively large. You can use or reference the converted geometry for modeling purpose. I just don't see a workflow that you can modify such geometry efficiently in Inventor at the moment unfortunately.

Many thanks!

[revyakin]

Johnson, OK, thank you. I thought that, in a mesh, every point in a triangle had an XYZ coordinate, and that this data could be converted into solvable geometries with faces and angles via the mesh converter tool. I will try and generate my own (probably much less complex) model of sufficient detail. I also need to understand the differences between obj, stl, igx etc files that are typically downloadable at CAD sharing resources.

[johnsonshiue]

Hi! One more thing to clarify. Yes, the mesh vertices are measurable. But, the vertices are limited to certain quantity, right? The more vertices you have, the more accurate the model becomes. Regardless, you can only measure when there is a vertex. For area within each mesh element, it is not measurable.

On a precise model, every single point can be measured. For example, on a curvy surface, you can intersect it with an axis to create a workpoint. But, you cannot do that with mesh. It is because mesh is like scaffolding. It is like you can "approximate" the shape of a building by looking at the scaffolding. But, you don't know exactly what the building look like. Precise model is like the building itself.

Many thanks!