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In this section of the tutorial, we use body constraints and model dimensions to control how the model updates.
Body constraints create relationships between model faces. For example, the vertical extrusions on this model are symmetrical, and the large radii are concentric with the holes.
Model dimensions are used to annotate the model, and to control the size and location of edges. You can lock dimensions to hold the size during updates. Usually, only critical dimensions remain locked, while other dimensions are locked during modeling to maintain size or proportions and then unlocked or deleted.
One of the advantages of direct modeling is that you can easily change the model geometry. Since body constraints and locked dimensions restrict this functionality, they are usually limited to cases where there is an important relationship.
- Open the tutorial file Body Constraints and Dimensions.dwg.
- Expand the Named Views folder in the browser and click Corner View, then press Home to zoom into the model. Select the Left face and start Move. As you drag the manipulator, the top radius moves but the hole does not. We can add a constraint to keep the radius and the hole concentric.
- Press Escape to cancel the change.
- Start the Body Constraint command from the Constrain and Dimension panel. Select the Center constraint type on the command ribbon, and then select the hole and the radius.
- Press Enter to create the constraint. A Constraints folder is added to the browser, and the faces highlight when you pause the cursor over the constraint. You cannot edit constraints, but you can delete them to make the faces independent again.
- Start move and select the hole. The initial triad orientation depends on where you clicked on the hole. Click the Reorient Triad button. Select one of the plane manipulators, and then the back face. Click the axis manipulator that is parallel to the hole, and then select the hole to align it.
NoteThe triad can have a different orientation, depending on the initial triad orientation and which manipulator plane you selected. Make sure one of the axis manipulators is vertical .
- Select the vertical manipulator and drag it upwards. The hole and the radius stay concentric, but the hole on the other side does not move. In this model, the extrusions on both sides move together because the back face connects them. The holes do not have a relationship because they were created separately.
- Press Esc to cancel the command. Start Body Constraints and select the holes.
NoteThe back face connects the extrusions, so they update together. You could also select either radius for the constraint and the model would have the same update behavior. However, if a cut is made in the back face of the part, the extrusions would not stay connected. A shaft goes through the holes, so they must be aligned even if the geometry changes.
- Return the model to the Isometric view and start the Dimension command. Select the edge of the angled face and the bottom edge of the cut. Click to place the dimension behind the model and press Esc to end the command. Double-click the dimension and enter 15. Move the cursor above and below the dimension- the anchor glyph indicates which edge is fixed. Position the cursor so the top face of the bracket remains fixed and press Enter.
- Start the Body Constraint command, select the Coplanar constraint type, and then select the angled faces.
- Start the Body Constraint command, select the Coplanar constraint type, and then select the angled faces. The anchor glyph indicates which face is fixed and which face moves. Activate the anchor for the face without the dimension and press Enter.
Adding the constraint causes the top face of bracket to tilt. The face with the dimension was not anchored, so it moved to align with the other face. Since the dimension was automatically locked when you edited it, the top face of the bracket moved to maintain that dimension.
- Click Undo to restore the model geometry. Click on the dimension, and then click the padlock button to unlock it. Apply the coplanar body constraint again, and make sure that the non-dimensioned face is anchored. Press Enter to apply the constraint. This time, only the face with the dimension moves, and the dimension updates with the new value.
- Double-click the dimension and enter 20. Position the cursor so the top face of the bracket remains fixed and press Enter- both faces update to the 20 degree angle. The anchor only effects the update behavior when the constraint is created. After that, either face can be changed and the other one updates to match.
In the next section of the tutorial, we look at more methods for using model dimensions to define geometry and create annotations.
The same model is used for the next section. We work with other model geometry, so you can keep the model open, or close it and open the original model again.