Surface Continuity

Three Types of Continuity Complex designs need to be built up from many surface patches. The relationship between these surface patches will give the design its character. Positional Continuity This is where surfaces meet at an angle—a sharp edge. Positional continuity is important if you need a ‘closed’ model that represents a solid object. This can be transferred successfully to another CAD system, have a volume calculated, or be tessellated to create a rapid prototype. Tangent Continuity This is the kind of continuity created by rounds or fillets. The join between the two surfaces is smooth, but, visually, you can see where one surface ends and the other one starts. There is a ‘highlight line’—the sort of line you would draw with a soft white pencil in a hand rendering. Curvature Continuity With curvature continuity, the join between the surfaces is smooth to touch and to see—it is hard to tell where one surface starts and the other ends. G0, G1, G2 These are standard terms used for the continuity conditions. Positional Continuity (G0) Tangent Continuity (G1) Curvature Continuity (G2)

Aligning Two Curves Object Edit>Align Positional (G0) Continuity 1 The Align Tool The Object Edit>Align tool can be used to align curves and surfaces with positional, tangent, or curvature continuity. A construction history relationship will be created so that continuity will be maintained while the curves or surfaces are modified. The Align tool has been used in this example to show how CVs are used to achieve the three levels of continuity. Understanding how CVs relate to continuity is important for trouble-shooting some of the advanced blending tools that you will use later in this course. Continuity and CVs Positional continuity requires the first CV of the aligned curve to be in the same position as the end CV of the curve being aligned to. Tangent continuity requires the second CV of the aligned curve to have a straight-line relationship with the second CV of the curve being aligned to. Curvature continuity requires the third CV of the aligned curve to be in a constrained relationship with the third CV of the curve being aligned to. Positional (G0) Continuity 1 CV required 1 2 Tangent (G1) Continuity 2 CVs required 1 2 Curvature (G2) Continuity 3 CVs required 3

Evaluating Curve Continuity Locators>Curve Curvature Click on a curve or curves to display the curvature plot. Positional Comb plot at different angles Continuity and CVs Positional Continuity The end points meet exactly, but the direction of each curve is different as shown by the ‘break’ in the comb plot. Tangent Continuity The end tangents of the curves are matched, meaning that the curves have the same direction at the point they meet. A round or fillet on a straight edge is smooth but clearly has a ‘jump’ in the curvature as it transitions from flat to a radius. Curvature Continuity Just as the curve directions match, the radius value is also matched so the rate of change of direction is the same. This gives a smoother result. Tangent Comb plot aligned but different radius values R1 R2 Curvature Comb plot aligned and radius value matched R1=R2

Aligning Two Surfaces Object Edit>Align Positional (G0) Continuity Align Tool Options Positional (G0) Continuity One row of CVs required 1 Tangent (G1) Continuity Two rows of CVs required 1 2 Curvature (G2) Continuity Three rows of CVs required 1 2 3

Evaluating Surface Continuity Diagnostic Shading Evaluating Surface Continuity Using ‘Zebra’ Stripes Increase the quality of tessellation to ensure an accurate evaluation. Positional Zebra stripes are disjointed Diagnostic Shading The Diagnostic Shading in the Control Panel is designed to analyze the surface quality. The ‘Zebra Stripe’ shader simulates the technique used in automotive design where a model is placed under strip lights. By changing your view, you can assess the quality of the highlights. In Alias, you will tumble the model under the zebra stripe reflections to get the same effect. Choose horizontal or vertical stripes as required to assess your model. Tangent Zebra stripes are the same width but not smooth Choose horizontal or vertical stripes Curvature Zebra stripes are smooth Increase the number of stripes

Blending Between Two Curves Degree 3 Curve Single span 4 CVs Degree 5 Curve Single span 6 CVs Surfaces: Tangency at both ends: 4 CVs Curvature at both ends: six rows of CVs Curvature at both ends: 6 CVs Single-span degree 5 curves are recommended for blending curves.

Construction Options Preferences>Construction Options Set the construction options before you start to model to define the accuracy of the continuity. Position Tangent Curvature Measuring Continuity Evaluate>Continuity>Surface Continuity Open the option window to set the level of continuity you want to check. Click Go, and then click on the join between two surfaces. A green locator indicates that continuity has been achieved. A yellow locator indicates a continuity problem. Position........0.1 mm Tangent........0.1 degrees Curvature.....0.1 Position........0.01 mm Tangent........0.1 degrees Curvature.....0.1 Position........0.002 mm Tangent........0.1 degrees Curvature.....0.1

When to Use Align Align doesn’t work successfully on adjacent edges: Align works well on one or two (opposite) sides of a surface: Using Align There are two ways of using the Align tool: Freeform Sculpting When sculpting a fairly free shape—cosmetics bottles for example—Align can be used successfully to create the main shapes for the design. Patching and Blending To use the Align tool for patching and blending surfaces on all four sides, you will need to use advanced modeling techniques covered in a later course. It is easier at this stage to use different surface tools to achieve complex blends. These will include the Surface Fillet, Freeform Blend, Bi-Rail, and Square surfaces. Align doesn’t work on periodic surfaces Align doesn’t work well on trimmed edges: Heavy Parameterization (but Align 2008 does)

Exercises EX1-Align-curve.wire EX2-Align-surface.wire EX3-Align-two-curves.wire EX4-Align-two-surfaces.wire EX5-Align-eval.wire

Other Continuity Tools: Surface Fillet Surfaces>Surface Fillet (Tangent) The basic operation of the Surface Fillet tool was covered in the ‘Intersecting and Trimming’ lesson. You will typically use Circular (Tangent) or Curvature. The same value will give different results: In the same space, curvature continuity gives a softer connection but a tighter transition. Constant Radius, Tangent Continuity

Surface Fillet Options Filleting Multiple Edges The Surface Fillet tool will create a blend surface between one set of surfaces and another set. Each set of surfaces must be tangent continuous for the fillet to work. Max Surf Spans If you are building a complex fillet, you may get a warning about Max Surf Spans. If you are building a concept model, you can ignore this warning. If you are planning to export your data to a CAD system, there may be a problem with stitching the surfaces together as a solid model. Fixed Radius, Variable Width Fixed Width, Variable Radius Variable Fillets Click on the blue line to add another radius value. Shift-click to remove. Use the middle mouse button to change the position of the radius locator.

Surface Fillet Options Recommended for best-quality layout of surfaces and regular hulls Recommended for quick, tidy modeling Flow Control and Continuity Occasionally, choosing different flow control options can affect the continuity. To check, turn on the Continuity Check option in the Surface Fillet tool. Green means continuity has been successfully achieved; yellow means there is a continuity break.

Other Continuity Tools: Freeform Blend Surfaces>Multi-Surface Blend>Freeform Blend Workflow: Create a gap between different shaped surfaces Create a Freeform Blend between the two edges Creates a tangent or curvature blend between two edges Shape The Shape slider gives you some limited control over the blend shape. It provides control over the ‘looseness’ or ‘tightness’ of the blend surface. If the value is greater than 1.0, the result is a blend that fits tighter to the corner of the input surfaces; if the value is less than 1.0, the result is a rounder blend that fits closer to the edges of the surface. 0.1 0.5 1 2 Chain Select will pick a series of edges.

Exercises EX6-Fillet-continuity.wire EX7-Fillet-options.wire EX8-Freeform-hood.wire EX9-Freeform-trunk.wire EX10-Freeform-options.wire

Projects P1-Electric-toothbrush.wire P2-Phone-casing.wire P3-Fillet-wheel.wire P4-Electronic-gadget.wire