I am writing an app to create 3D objects with curved surfaces such as a metal cabinet knob using SceneKit and Model I/O. I want the surfaces to be smooth so that edges between adjacent polygon faces are not visible. According to the documentation for MDLMesh.addNormals(withAttributeNamed: creaseThreshold:), a positive creaseThreshold value lower than 1.0 will interpolate sharper angles between faces into smooth surfaces. I have not been able to get this to work, and I need help with it. The lines of code where the problem occurs are shown here. let mesh = MDLMesh(scnGeometry: surfaceGeometry) // mesh.addNormals(withAttributeNamed: "MDLVertexAttributeNormal", creaseThreshold: 0.9) surfaceGeometry = SCNGeometry(mdlMesh: mesh) When the code is executed with middle line commented out, the knob object is rendered as shown in the screenshot. When that line is not commented out, mesh is altered and the SCNNode for the knob is created with no errors, but the node is not rendered. The questions I have are: (1) What changes do I need the make to the code so that the node will be rendered with a smooth surface?, and (2) what is the recommended way of smoothing a curved surface so that edges between faces are not visible? The full code for the function and a screenshot of the faceted knob object are attached. ![]("https://developer.apple.com/forums/content/attachment/a17feca7-ed6f-440c-add6-760a1cbf8778" "title=Screenshot cabinet knob with faceted surface.png;width=790;height=568") code-block func cabinetKnob() -> SCNNode { let controlPoints: [(x: Float, y: Float)] = [ (0.728,-0.237), (0.176,-0.06), (0.202,0.475), (0.989,0.842), (-0.066,1.093), (-0.726,0.787) ] let pairs = bsplinePath(controlPoints) var knobProfile = [SCNVector3]() for (x,y) in pairs { knobProfile += [ SCNVector3(x: CGFloat(x), y: CGFloat(y), z: 0)] } let nProfiles = 64 // create knob by rotating knobProfile about y-axis let aIncrement: CGFloat = 2 * CGFloat.pi / CGFloat(nProfiles) // ~6 degrees var angle: CGFloat = 0 var knobVertices = knobProfile.map( { $0 } ) angle = 0 for _ in 1...nProfiles { angle += aIncrement // rotate knobProfile about y-axis knobVertices += knobProfile.map( { $0.rotate(about: .y, by: angle) } ) } let source = SCNGeometrySource(vertices: knobVertices) var indices = [[UInt16]]() var i: UInt16 = 0 var j: UInt16 = UInt16(knobProfile.count) // 1st vertex of next profile for k in 0...nProfiles { var stripIndices = [UInt16]() if k == nProfiles { j = 0 } for _ in 0...knobProfile.count-1 { stripIndices += [i, j] i += 1; j += 1 } indices += [stripIndices] } let elements: [SCNGeometryElement] = indices.map( { SCNGeometryElement(indices: $0, primitiveType: .triangleStrip) } ) var surfaceGeometry = SCNGeometry(sources: [source], elements: elements) let mesh = MDLMesh(scnGeometry: surfaceGeometry) // mesh.addNormals(withAttributeNamed: "MDLVertexAttributeNormal", creaseThreshold: 0.9) surfaceGeometry = SCNGeometry(mdlMesh: mesh) let aluminum = SCNMaterial() aluminum.lightingModel = SCNMaterial.LightingModel.physicallyBased aluminum.diffuse.contents = NSColor(srgbRed: 0.95, green: 0.95, blue: 0.95, alpha: 1.0) aluminum.roughness.contents = 0.2 aluminum.metalness.contents = 0.9 aluminum.isDoubleSided = true surfaceGeometry.materials = [ aluminum ] let node = SCNNode(geometry: surfaceGeometry) return node }