Two-Dimensional Constraints Procedure
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Two-Dimensional Constraints When you create a sketch in Inventor, the program makes inferences about the kinds of geometry you are creating. These inferences are called geometric constraints and are used to enforce rules you want your initial sketch to follow. These rules might include parallel lines, perpendicular lines or axes, tangent or concentric circles, etc. Having the geometric constraint defined can simplify your work. Some geometric constraints work only with lines while others work with arcs or circles. This tutorial is designed to help you apply and manipulate constraints. Try each one.
Procedure: Start by creating a new part file in Inventor, a Standard.ipt. In the Inventor graphics window, right click and click on Create Constraints. What you see are the 11 types of geometric constraints that are available in Inventor.
Fig. 1 Geometric Constraints Perpendicular is a constraint that causes lines or axes of curves to meet at right angles. This constraint is often inferred while sketching. Parallel causes two or more lines or ellipse axes to be equidistant from each other.
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Tangent is used to cause two arcs or a line and an arc to intersect at a single point perpendicular to the arc’s radius. (They do not have to physically share the common point - the point could be an extension of one of the entities.) Coincident fixes two points together, or fixes a point to a curve. Concentric causes two or more arcs, circles, or ellipses to share the same center point. Collinear causes two lines or ellipse axes to lie along the same line. Horizontal causes lines, ellipse axes, or pairs of points to lie parallel to the X axis of the sketch coordinate system. Vertical causes lines, ellipse axes, or pairs of points to lie parallel to the y axis of the sketch coordinate system. Equal forces line segments to be the same length and arcs or circles to have the same radius. Fix constrains points or curves to a specific point on the sketch coordinate system. Symmetry causes selected lines or curves to become symmetrically constrained about a selected line.
Sketch 1: Use the line command
to sketch this shape:
Fig. 2 First Sketch Place your cursor over a corner. Left click (hold) and drag the shape around. Notice that you can move each corner, even to the point of changing its shape. To see which constraints have been applied to your sketch, choose either the Show Constraints command from the tool bar
and click on each of your sketch lines, or right click
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in the graphics window and choose Show all Constraints.
Fig. 3 Constraints shown If any constraints appear other than the ones shown in Figure 3, delete them. To delete a constraint, highlight the individual constraint, right click and select delete. Let’s add some constraints to the sketch. Right click in the graphics window to bring up the sketch menu. Move down the menu to the Create Constraint option, and select the Horizontal constraint. Click on the bottom line of your sketch. Add a Fix constraint to the bottom line from the right click menu. Notice that there are now more constraints added to the list. If you try to move the line by left clicking and dragging, it resists that effort.
Fig. 4 Sketch with Horizontal and Fix constraints Add a perpendicular constraint between the bottom line and the line on the right. Now add a fix constraint to the line on the right.
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Fig. 5 Perpendicular and Fix constraints added Add a parallel constraint between the bottom line and the top line. Add a vertical constraint to the line on the left. You should now have a rectangle that you cannot drag into any other shape other than a rectangle.
Fig. 6 Parallel and Vertical Constraints Let’s add some dimensions: First, hide the constraints. Right click in the graphics window and choose Hide all Constraints. Then right click and choose Create Dimension. Click on the bottom line, drag down and let go. Put your cursor right over the dimension showing, and in the edit dimension box enter 4, as is shown in Figure 7.
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Fig. 7 Edit Dimension Dialog Box Either click on the green checkmark, or hit return on your keyboard. That side will now become 4 inches in length. (NOTE: If the Edit Dimension box does not appear automatically when you place the dimension, press the Escape key to exit the dimension tool. From the pull down toolbar at the top of your screen, click on the Tools menu and select Application Options. In the Options dialog box, select the Sketch tab. Place a checkmark in the box that says, “Edit dimensions when created.” Click on the Apply button and then click on Okay.) Place a dimension of 3 inches on the left side by repeating the steps shown here. Right click and choose Done. It might be necessary to re-size your screen to see the image.
Fig. 8 Finished Sketch
Sketch 2 Create a sketch similar to the one shown in Figure 9 using the line command. (To create the arcs, left click, hold and drag.) The numbers on the outside are there for reference only. You won’t be adding them to your sketch.
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Fig. 9 Second Sketch Use the Show Constraints icon to view the existing constraints on your sketch. Delete all of the constraints except the Coincident constraint. When you are done, your sketch should look like the one shown in Figure 10.
Fig. 10 Apply the Fix constraint to the center point of arc segment #1 (as labeled in figure 9) to lock the position of the arc in place.
Fig. 11 Fix constraint used on left radius Now choose the tangent constraint and work on pairs of sections. Create a tangent constraint between arc segment #1 and line segment #2, between line segment #2 and arc segment #3, etc., working around the sketch. When you have finished, your sketch will look like the one in Figure 12.
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Fig. 12 Tangent constraint Now choose the Horizontal constraint and select the center points of arcs 1 and 5 (they are the arcs on the right and on the left of the image). This will align the arc centers parallel to the x-axis. Choose the Vertical constraint and select the center points of arcs 3 and 7 (they are the arcs on the top and bottom of the image). This will align the arc centers parallel to the y-axis. Use the equal constraint to force the arcs at the top and the bottom to be equal, and the ones on the right and the left to be equal. The shape may start to warp some, but will correct itself when dimensional constraints are added. Turn off the constraint visibility by right-clicking in the graphics window and selecting Hide All Constraints. Add the dimensions shown in figure 13.
Fig. 13 Sketch with Dimensions
Sketches 3 and 4 and 5 Click here to open 2-D constraints practice.
Click on the icon at the top of the screen and then click on any edge of any figure. You are now ready to deal with the sketches shown there. (If the constraints are visible, right click in the screen and Hide Constraints.) Start with the sketch in the upper left corner, shown here as figure 14.
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Fig. 14 Sketch #3 Apply the geometric constraints necessary to have the sketch look like the one in figure 15. Any dimensions in parentheses are there for your reference only. Think of the relationships between the sketch geometry shown and apply the geometric constraints to create those relationships. If you have constrained this figure correctly with geometric constraints, you won’t need those dimensions to create the sketch shown.
Fig. 15 Finished Sketch Sketch #4 is shown in Figure 16. Make it look like the one in Figure 17.
Fig. 16 Sketch #4
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Fig. 17 Constraints completed For the final sketch constraints activity, take sketch #5 (shown in figure 18) and make it look like the one in figure 19.
Fig. 18 Sketch #5
Fig. 19 Constraints completed
Additional Exercises: Draw, constrain and dimension each shape shown here.
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Two-Dimensional Constraints When you create a sketch in Inventor, the program makes inferences about the kinds of geometry you are creating. These inferences are called geometric constraints and are used to enforce rules you want your initial sketch to follow. These rules might include parallel lines, perpendicular lines or axes, tangent or concentric circles, etc. Having the geometric constraint defined can simplify your work. Some geometric constraints work only with lines while others work with arcs or circles. This tutorial is designed to help you apply and manipulate constraints. Try each one.
Procedure: Start by creating a new part file in Inventor, a Standard.ipt. In the Inventor graphics window, right click and click on Create Constraints. What you see are the 11 types of geometric constraints that are available in Inventor.
Fig. 1 Geometric Constraints Perpendicular is a constraint that causes lines or axes of curves to meet at right angles. This constraint is often inferred while sketching. Parallel causes two or more lines or ellipse axes to be equidistant from each other.
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Tangent is used to cause two arcs or a line and an arc to intersect at a single point perpendicular to the arc’s radius. (They do not have to physically share the common point - the point could be an extension of one of the entities.) Coincident fixes two points together, or fixes a point to a curve. Concentric causes two or more arcs, circles, or ellipses to share the same center point. Collinear causes two lines or ellipse axes to lie along the same line. Horizontal causes lines, ellipse axes, or pairs of points to lie parallel to the X axis of the sketch coordinate system. Vertical causes lines, ellipse axes, or pairs of points to lie parallel to the y axis of the sketch coordinate system. Equal forces line segments to be the same length and arcs or circles to have the same radius. Fix constrains points or curves to a specific point on the sketch coordinate system. Symmetry causes selected lines or curves to become symmetrically constrained about a selected line.
Sketch 1: Use the line command
to sketch this shape:
Fig. 2 First Sketch Place your cursor over a corner. Left click (hold) and drag the shape around. Notice that you can move each corner, even to the point of changing its shape. To see which constraints have been applied to your sketch, choose either the Show Constraints command from the tool bar
and click on each of your sketch lines, or right click
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in the graphics window and choose Show all Constraints.
Fig. 3 Constraints shown If any constraints appear other than the ones shown in Figure 3, delete them. To delete a constraint, highlight the individual constraint, right click and select delete. Let’s add some constraints to the sketch. Right click in the graphics window to bring up the sketch menu. Move down the menu to the Create Constraint option, and select the Horizontal constraint. Click on the bottom line of your sketch. Add a Fix constraint to the bottom line from the right click menu. Notice that there are now more constraints added to the list. If you try to move the line by left clicking and dragging, it resists that effort.
Fig. 4 Sketch with Horizontal and Fix constraints Add a perpendicular constraint between the bottom line and the line on the right. Now add a fix constraint to the line on the right.
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Fig. 5 Perpendicular and Fix constraints added Add a parallel constraint between the bottom line and the top line. Add a vertical constraint to the line on the left. You should now have a rectangle that you cannot drag into any other shape other than a rectangle.
Fig. 6 Parallel and Vertical Constraints Let’s add some dimensions: First, hide the constraints. Right click in the graphics window and choose Hide all Constraints. Then right click and choose Create Dimension. Click on the bottom line, drag down and let go. Put your cursor right over the dimension showing, and in the edit dimension box enter 4, as is shown in Figure 7.
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Fig. 7 Edit Dimension Dialog Box Either click on the green checkmark, or hit return on your keyboard. That side will now become 4 inches in length. (NOTE: If the Edit Dimension box does not appear automatically when you place the dimension, press the Escape key to exit the dimension tool. From the pull down toolbar at the top of your screen, click on the Tools menu and select Application Options. In the Options dialog box, select the Sketch tab. Place a checkmark in the box that says, “Edit dimensions when created.” Click on the Apply button and then click on Okay.) Place a dimension of 3 inches on the left side by repeating the steps shown here. Right click and choose Done. It might be necessary to re-size your screen to see the image.
Fig. 8 Finished Sketch
Sketch 2 Create a sketch similar to the one shown in Figure 9 using the line command. (To create the arcs, left click, hold and drag.) The numbers on the outside are there for reference only. You won’t be adding them to your sketch.
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Fig. 9 Second Sketch Use the Show Constraints icon to view the existing constraints on your sketch. Delete all of the constraints except the Coincident constraint. When you are done, your sketch should look like the one shown in Figure 10.
Fig. 10 Apply the Fix constraint to the center point of arc segment #1 (as labeled in figure 9) to lock the position of the arc in place.
Fig. 11 Fix constraint used on left radius Now choose the tangent constraint and work on pairs of sections. Create a tangent constraint between arc segment #1 and line segment #2, between line segment #2 and arc segment #3, etc., working around the sketch. When you have finished, your sketch will look like the one in Figure 12.
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Fig. 12 Tangent constraint Now choose the Horizontal constraint and select the center points of arcs 1 and 5 (they are the arcs on the right and on the left of the image). This will align the arc centers parallel to the x-axis. Choose the Vertical constraint and select the center points of arcs 3 and 7 (they are the arcs on the top and bottom of the image). This will align the arc centers parallel to the y-axis. Use the equal constraint to force the arcs at the top and the bottom to be equal, and the ones on the right and the left to be equal. The shape may start to warp some, but will correct itself when dimensional constraints are added. Turn off the constraint visibility by right-clicking in the graphics window and selecting Hide All Constraints. Add the dimensions shown in figure 13.
Fig. 13 Sketch with Dimensions
Sketches 3 and 4 and 5 Click here to open 2-D constraints practice.
Click on the icon at the top of the screen and then click on any edge of any figure. You are now ready to deal with the sketches shown there. (If the constraints are visible, right click in the screen and Hide Constraints.) Start with the sketch in the upper left corner, shown here as figure 14.
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Fig. 14 Sketch #3 Apply the geometric constraints necessary to have the sketch look like the one in figure 15. Any dimensions in parentheses are there for your reference only. Think of the relationships between the sketch geometry shown and apply the geometric constraints to create those relationships. If you have constrained this figure correctly with geometric constraints, you won’t need those dimensions to create the sketch shown.
Fig. 15 Finished Sketch Sketch #4 is shown in Figure 16. Make it look like the one in Figure 17.
Fig. 16 Sketch #4
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Fig. 17 Constraints completed For the final sketch constraints activity, take sketch #5 (shown in figure 18) and make it look like the one in figure 19.
Fig. 18 Sketch #5
Fig. 19 Constraints completed
Additional Exercises: Draw, constrain and dimension each shape shown here.
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