AUGIWorld Magazine - January/February 2008 - (Page 22) AUTODESK INVENTOR Constraint Fundamentals happen with inadvertent mouse clicks later on. I start at the origin (X, Y, Z are all 0), and create my first line, used for a center point for a circle or arc. From there, I continue rough drawing the rest of my geometry. Some constraints are being applied as I continue my sketching. You will see an icon pop up with your cursor as you create your lines, circles, and arcs. Those are some basic constraints, such as perpendicular, parallel, tangent, concentric, and end points that are coincident. There Figure 2: Rough sketch may be another constraint or two also applied. You will have to apply others as needed to fully constrain the sketch, which we will discuss in further detail. See Figure 1 for the icons in the constraint tool bar. I have completed my rough sketch (it is rough as there are no dimensions, and not all the geometry is constrained). See Figure 2. See the line with the arrow pointing to it? That is the line I am constructing—it is being constrained parallel to the bottom line. Hint: If you need the Figure 3: Locking point new line to be parallel or Warning: Be careful how you create your perpendicular to a specific line, start your new line, then momentarily lines. When you are placing lines at angles, hover your curser above the line to which you might get angled lines that could be you want your new line to be parallel or created parallel or tangent to other angled perpendicular. The corresponding con- lines already on your sketch. What I do is exaggerate the angle, then assign a dimenstraint will show above the line. The first line you create, if horizontal sion to correct the angle that I need. Once you have finished your sketch, the or vertical, will automatically have an assigned constraint. I will describe later how next operation is to lock the point at the to show constraints and how to remove origin. If you look in the lower right corner, there is a message that determines how unwanted constraints. w w w. A U G I . c o m When creating a new part with Autodesk Inventor®, a sketch pad opens. This is where you lay out the outline of your geometry that you will need to extrude, rotate, sweep, etc., to create the first feature of your solid model. If you are accustomed to working with AutoCAD®, you will need to re-arrange your thinking cap just a bit. You start by drawing or sketching what you need for your design. Then add constraints and dimensions, after the geometry has been drawn or sketched. Constraints—what, why, and how A constraint is a control that is needed to constrain the geometry. Got it? No? A constraint is how geometry is related to other geometry within your sketch. Better? I hope so. Geometry related to other geometry… think about that for a minute. Well, parallel, perpendicular, concentric, linear — isn’t that how a line is related or constrained to another line? Concentric, as with two circles, or circle and an arc? Figure 1: Constraint toolbar A fully constrained sketch means that there are no “floating” geometry entities. I’ll define floating with this example: if I were to grab an end point, center point, or part of the geometry (line or circle), I could pull it or stretch and drop in a new location. Nothing will change on its own later in my design. I’m sure most of us have been working on a design, and then it suddenly changes and we have no idea why. Just a sudden click on something and the geometry changes. If you fully constrain your sketch, and all sketches, then that magically changing part tends not to 22 http://www.AUGI.com
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