{"id":60745,"date":"2023-08-18T06:00:00","date_gmt":"2023-08-18T13:00:00","guid":{"rendered":"https:\/\/www.autodesk.com\/products\/fusion-360\/blog\/?p=60745"},"modified":"2024-03-18T18:37:43","modified_gmt":"2024-03-19T01:37:43","slug":"fusion-360-3d-modeling-singularities-non-manifold-topology","status":"publish","type":"post","link":"https:\/\/www.autodesk.com\/products\/fusion-360\/blog\/fusion-360-3d-modeling-singularities-non-manifold-topology\/","title":{"rendered":"The 7 Deadly Sins of Fusion 360 3D Modeling Pt.\u00a03: Singularities & Non-Manifold Topology"},"content":{"rendered":"\n

Let’s uncover two common causes of modeling failures in Fusion 360 and learn how to avoid them: Singularities and NonManifold Topology.\u00a0<\/em><\/p>\n\n\n\n

Have you ever tried to model a shape with Autodesk Fusion 360 and failed? I have, many times!\u00a0In the previous post in this series<\/a>, we learned about the 3D Modeling deadly sins of \u2018Near Coincidence\u2019 and \u2018Sliver Faces\u2019, and we learned how to avoid them!\u00a0<\/p>\n\n\n\n

In this post, we\u2019ll learn why a singularity is not a good thing, and we\u2019ll understand how Fusion 360 uses the concept of Manifold Topology to define our solid objects. <\/p>\n\n\n

Singularities\u00a0<\/h2>\n\n\n

In \u2018Get Smart with Fusion 360\u2019 Pt. 4<\/a>, we learned that the Autodesk Shape Manager (ASM) defines a Loft mathematically as a four-sided shape. ASM will fit the lofted surface to the profiles we supply.\u00a0<\/p>\n\n\n\n

If we supply one Edge Section and one Point Section to the Loft command, ASM will create a three-sided loft. The \u201ctip\u201d of the three-sided loft is called a singularity. Singularities can also be formed when revolving a surface.\u00a0<\/p>\n\n\n\n

Singularities themselves aren\u2019t a problem, but they can cause problems downstream, particularly when offsetting surfaces.\u00a0<\/p>\n\n\n\n

\"fusion-360-3d-modeling-singularities\"<\/figure>\n\n\n\n

If you’re having problems with a non-four-sided surface, the easiest way to diagnose Singularities is with the Isocurve Analysis Tool. If the isocurves converge on a single point, you have a singularity!\u00a0<\/p>\n\n\n\n

If you can, try swapping the problem surface with a boundary patch. The boundary patch tool always creates a four-sided surface that is Trimmed to the input geometry (instead of Fitted) to avoid singularities.\u00a0<\/p>\n\n\n

Non-manifold topology\u00a0<\/h2>\n\n\n

Manifold Topology is the way we describe how Fusion 360 recognizes that a shape is a solid. If the shape is open, Fusion 360 will create a surface model. If the shape is closed, Fusion 360 knows that it has a solid.\u00a0<\/p>\n\n\n\n

\"fusion-360-3d-modeling-non-manifold-topology\"<\/figure>\n\n\n\n

There are two conditions for a shape to be ‘closed’:<\/p>\n\n\n\n

    \n
  1. Internal voids must be completely enclosed by Faces. <\/li>\n\n\n\n
  2. Faces must have an \u2018inside\u2019 and an \u2018outside\u2019.\u00a0<\/li>\n<\/ol>\n\n\n\n

    There are additional conditions for a shape to be ‘manifold’: \u00a0<\/p>\n\n\n\n

      \n
    1. Each Edge can only be shared by two Faces.  <\/li>\n\n\n\n
    2. Each Vertex cannot be a \u201cpinch\u201d point in the solid (a point where two or more closed volumes join at a single vertex).\u00a0<\/li>\n<\/ol>\n\n\n\n

      You can see that it’s possible for geometry to be both closed and non-manifold. Geometry that fails to meet these four conditions can cause unexpected outcomes.\u00a0<\/p>\n\n\n\n

      Non-Manifold topology causes ambiguities which Fusion 360 can find confusing. The classic example is two cubes sharing an edge. This edge is non-manifold because four faces share a single edge.<\/p>\n\n\n\n

      When we try to fillet this edge, ambiguity arises because there are four equally valid solutions. Which solution do we expect? <\/p>\n\n\n\n

      If you are having trouble with non-manifold geometry, try re-ordering the Timeline, creating multiple bodies, or adding temporary supporting features.\u00a0<\/p>\n\n\n\n

      \"fusion-360-3d-modeling-non-manifold-topology-result-options\"<\/figure>\n\n\n

      The 7 Deadly Sins of Fusion 360 3D Modeling Pt 4: Loose Tolerances\u00a0<\/h2>\n\n\n

      In the final post of this series, we\u2019ll learn how we can get into trouble if we allow loose tolerances!\u00a0Read the rest of the series below:<\/p>\n\n\n\n

      Part 1: High Curvature & Near Tangency
      <\/a>      Part 2: Near Coincidence & Sliver Faces\u00a0<\/a><\/p>\n\n\n\n

      This blog post is based on an Autodesk University class. You can read the handout, download a dataset, and try out some exercises that illustrate the Seven Deadly Sins from the Autodesk University website here:<\/em>\u00a07 Deadly Sins of 3D Part Modeling in Fusion 360<\/em><\/a>.<\/p>\n","protected":false},"excerpt":{"rendered":"

      Let’s uncover two common causes of modeling failures in Fusion 360 and learn how to avoid them: Singularities and NonManifold Topology.\u00a0<\/p>\n","protected":false},"author":5165,"featured_media":60747,"menu_order":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"inline_featured_image":false,"footnotes":""},"categories":[353,476],"tags":[392,430,356],"coauthors":[],"class_list":["post-60745","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-getting-started","category-tutorials","tag-3d-modeling","tag-cad","tag-tutorial","dhig-theme--light"],"acf":[],"yoast_head":"\nHow to Avoid Singularities & Non-Manifold Topology in Fusion 360<\/title>\n<meta name=\"description\" content=\"Let's uncover two common causes of modeling failures in Fusion 360 and learn how to avoid them: Singularities & Non-Manifold Topology.\u00a0\" \/>\n<meta name=\"robots\" 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