Capturing Design Intent in Autodesk Inventor Using Construction Geometry

Transcription

1 11/29/2006-3:00 pm - 4:30 pm Room:Marcello (MSD Campus) Capturing Design Intent in Autodesk Inventor Using Construction Geometry David Piggott - Quantum Training Centers, Inc. MA24-5 Learn how to take full advantage of sketch linetypes including construction and centerline geometry, center points, and driven dimensions. Use of these simple tools allows you to capture your design intent while creating your part models. You will improve your modeling accuracy, consistency, and overall productivity with the use of these tools. A variety of modeling techniques will be demonstrated and discussed that take advantage of these tools and contrasts them with other methods of construction. This class will benefit all levels of Inventor users who create and modify part models. About the Speaker: Based in Grand Rapids, Michigan, David provides custom training and consulting services to Autodesk product users throughout the Midwest, and classroom training for Quantum Training Centers, Inc., an Autodesk Authorized Training Center. David uses both AutoCAD and Inventor software, creating product designs for his customers. He has over 17 years of teaching experience in CAD, 3D solid modeling, and CNC programming. He is also a journeyman mold maker. David obtained a bachelor s degree in Manufacturing Engineering, and an associates degree in Machine Tool Technology from Ferris State University. david@quantumtraininggr.com Stay Connect to AU all year at

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3 (The following text is adapted from Autodesk Official Training Courseware (AOTC) title Autodesk Inventor 11: 3D Curves, Sketches & Construction Geometry. This excerpt is being used with the written permission of Autodesk) Capturing Design Intent Using Construction Geometry This lesson describes the use of construction geometry to capture design intent and add intelligence to sketches on your parts. All sketches, regardless of their complexity, may require the use of construction geometry to be fully constrained. The use of construction geometry improves your modeling accuracy, consistency, and overall productivity. The following image displays a clamp for a center rest. This is a cast part and the ends are not finished. The design intent is for the counterbored holes to be located in relationship to the center clearance hole and for the center clearance hole to remain in the middle of the clamp. Reference geometry is used to constrain the hole center points to the middle of the block in both directions and then the counterbored holes are located using those same construction lines. Objectives After completing this lesson, you will be able to: Describe the different types of construction geometry. State the guidelines for using construction geometry. Create and use sketch points. Create and use driven dimensions. 2

4 Introduction to Construction Geometry You may already have used centerlines, construction lines, center points, and driven dimensions at some point, but have not yet made them a permanent part of your workflow. Each of these tools better enables you to capture your design intent as you work, and to keep the design intent as changes are introduced throughout the design process. These tools are especially useful as you begin to use 3D sketches. The following image illustrates a 3D spline with end and shape points coincident to construction geometry. Construction geometry is used on both profiles to constrain the 3D spline to the midpoint of the profile. Construction points are controlled with dimensional constraints, illustrated here by dashed lines, running perpendicular to both profiles from their midpoints outward and moving perpendicular downward on the left and upward on the right. These lines do not actually exist; what does exist are the points that the 3D spline passes through. The 3D spline is then created using the construction points. You can change the spline curvature by modifying the dimensional constraints of these points. Definition of Construction Geometry The following table lists the different types of construction geometry and how they are used. Linetype Construction Centerline Sketch Point Description Construction lines are used to aid in constructing and constraining normal geometry. You use construction lines when you need additional geometry to constrain a sketch but do not want that additional geometry to participate in defining the profile for the feature. The Centerline linetype is another type of Construction linetype. It can be used to define the centerline about which to revolve a profile to create a revolved feature. When you add dimensions between centerlines and other sketch geometry, they are treated as diameter dimensions. The Point/Center Point tool creates sketch points or center points in 2D and 3D sketches. For 3D sketches you can place and constrain sketch points to the vertices of existing geometry or in relationship to other geometry in the sketch. You use these points to help position or create 3D sketch geometry. Driven Dimension A driven dimension does not control the shape or size of your sketch, it simply reflects the value as controlled by other constraints and dimensions. 3

5 The following image illustrates 3D geometry being controlled by sketch points. The short dashed line on the left edge is a construction line. The dashed lines moving away and to the right represent dimension constraints controlling the location of a construction point. The 3D spline is created using the construction points. You change the shape of the spline by modifying the dimension constraint of the construction point. In the lower image, the linear dimension is changed from 170 to 200. The spline adjusts to reflect the change in location of the construction point. Example of Construction Geometry In the following illustration, a construction circle is used to center a circular cutout for a triangular exhaust flange. By creating a construction circle tangent to all sides of the triangle, the center point of the construction circle can be used to locate the center point of the circle that is used for the cutout. 4

6 2D sketch with construction geometry 3D parametric part model Construction circle tangent to all sides of the triangle Center point of construction circle Circle used for cutout location Driven Dimension The 47 mm dimension is shown in parentheses indicating that it is a driven dimension. While working through your design process, you may want to keep track of dimensional stackups and overall dimensions that are controlled by interior features. By placing a driven dimension as the overall dimension, you can keep better track of your design intent. 5

7 Construction Points The illustration on the left is a 3D spline created through a set of nonplanar points. This 3D spline is then used with a profile and the Sweep tool to produce a wave washer as shown on the right. Guidelines for Using Construction Geometry Construction geometry makes it possible to enforce your design intent. Without construction geometry, many features could not be created and their behavior would not be predictable when making changes. Use of construction lines, points, and driven dimensions provides the most efficient methods of construction possible. Construction Geometry Guidelines Follow these guidelines when creating and using construction geometry. Both sketch points and center points can be used to locate holes. Create a pattern of your center points prior to starting the Hole tool so that all holes of the same size can be created with a single hole feature. Use sketch points to control both 2D and 3D sketch geometry. Make sure you fully constrain the points to enforce your design intent. Use driven dimensions liberally; they help you keep track of your design intent as you work. Use your driven dimensions in equations of parametric dimensions to enforce your design intent. Example of Using a Driven Dimension in an Equation The following illustration demonstrates the use of both construction lines and driven dimensions to enforce design intent. The construction line (1) is coincident to the midpoints of the slot in order to position the slot by its midpoint. The overall dimensions of the part (2) are controlled by the box that the cover fits on, thus they are applied as driven dimensions. Notice that the slot location is controlled by a formula (3) that uses the driven dimension as its base. The slot is positioned 1/3 the distance from the right edge and 1/4 the distance of the overall from the top edge. By locating the slot in this manner, the slot maintains the 1/3 and 1/4 design intent when the overall size of the box and cover are modified. 6

8 Introduction to Creating and Using Points The most common use for center points in 2D sketches is for locating holes. The Hole tool automatically selects all center points from a 2D sketch for hole placement. Sketch points are used to generate 3D curves and locate your 3D sketch geometry. The following illustration shows a threaded hole placed on a curved edge. You use a center point to locate the hole based on your design criteria. 7

9 Tools for Creating Sketch Points The Standard toolbar contains a single button that determines which type of point is created, either a center point for hole placement or a sketch point. When this Center Point tool is active, your points are displayed like small cross hairs, as shown on the right. When the Center Point tool is not active, your sketch points are displayed as a single dot, as shown on the left. The selected mode remains active until you click the button again. To convert a sketch point to a hole center point, select the sketch point and then click the Center Point style button on the Standard toolbar. Tip Procedure: Creating Holes Using a 2D Center Point Common methods of locating a hole include the linear and concentric methods. However, you often cannot determine a hole placement with these methods. To use the From Sketch method of hole placement, you create a center point using the Point, Center Point tool. The following steps outline the procedure you follow to create a hole feature with a 2D center point. 1. Create a 2D sketch on the desired face or work plane of the part. 8

10 2. Project part geometry and work features as needed to accurately locate your sketch point. 3. Create the center point using the Point, Center Point tool. 4. Constrain the center point to the desired location. 5. Create the hole using the Hole tool. Procedure: Controlling a Spline Using Sketch Points Sketch points are used in both 2D and 3D sketch applications. The following list outlines the procedure you follow to control a spline using sketch points. The spline is then used by the Split tool to create a contoured face. 9

11 1. Create a 2D sketch on the desired face or work plane of the part. Project geometry as needed for locating your sketch points. 2. Create the sketch points used to control the spline shape. Add constraints as needed to locate the points. 3. Create the spline to be used by the Split tool. 4. Use the Vertical and Horizontal constraint tools to align the spline points with the sketch points. The alignment in this illustration is shown by the dashed lines for clarification only. These lines are not created with the constraint tools. 5. Adjust the spline shape by modifying the sketch point locations. Observe how the spline changes. 10

12 6. Use the spline to split the part. Introduction to Creating and Using Driven Dimensions You use driven dimensions to indicate the current size or location of a feature. The driven dimension updates if the part changes. You can use driven dimensions in a function for other dimensions just as you do with normal dimensions. The following illustration shows dimension parameter d34 as a function of the driven dimension parameter d33. Driven Dimension Overconstrained 11

13 Procedure: Creating Driven Dimensions for Overconstrained Sketches When adding a dimension would result in overconstraining the sketch, you are prompted to create the new dimension as a driven dimension, or to cancel to not create a dimension at all. In this example, the Box Cover sketch is created as adaptive geometry to the underlying module box. All dimensions applied to the main cover shape result in overconstraining the sketch. The following steps outline the procedure you follow to create a driven dimension that would otherwise overconstrain a sketch. 1. With your sketch active, create a General Dimension. 2. When notified of the overconstrained condition, click Accept to create the driven dimension. 3. Your dimension is displayed inside parentheses to indicate that it is a driven dimension. Procedure: Changing a Normal Dimension to a Driven Dimension If your design intent requires internal dimensions to control the sketch shape rather than an overall dimension, you can change the overall dimension to a driven dimension and then add the normal parametric dimension to the inside feature. The following steps outline the procedure you follow to change a normal parametric dimension into a driven dimension. 1. With your sketch active, select the overall dimension. 12

14 2. On the Standard toolbar, click Driven Dimension. 3. Your dimension is displayed inside parentheses to indicate that it is a driven dimension. 4. Add your additional inside dimension and set its value. Notice that the driven dimension is updated to reflect the overall size. Specific Examples shown in class will be available via the AU website following AU. 13