Episode 2 Sketching (circle)

We left off with my new file and I selected the ‘Circle’ tool, and I anchored the center of the circle at the origin (0,0,0). This brings up the concept of ‘Constraints’ or 2D Constraints, and we will delve in much further as we go along. By anchoring the center of the circle to the origin we have applied a constraint that tells Inventor that the center of the circle is at 0,0 (x,y in this sketch). That leaves this sketch with only one constraint and/or dimension to ‘fully constrain’ the sketch. What Inventor is looking for in this case is either the diameter or the radius of the circle.

In the case of circles to create a solid, Inventor (or any solid modeler) needs to know where the center of the circle is and the diameter/radius. Inventor will allow us to create a solid without the dimension or location of the center. Caution is advised here, it will do it, but it is much harder for it to do so. As mentioned in Episode 1, it is always better to fully constrain your sketch.

When we have created the circle on the screen all that is left to do is give it the size. Using the dimension tool pick on the edge of the circle. When you are in the dimension tool, and you are near geometry the dimension tool recognizes, it will show a ‘glyph’ near your cursor showing the type of dimension that it is about to apply. In this case the diameter. It is an option at this point to right-click for a pop-up menu, and change your selection to a radius.

By default (in a new Inventor out of the box) Inventor will figure out the size of the circle you created and give you that dimension when you left-click to place the dimension. Then you left-click on the dimension and an edit dimension tool will appear. When you change the dimension to the value that you desire, the circle (in this case) will change to that size. You can change this behavior so that the Edit Dimension tool appears as soon as you place the dimension. Select the ‘Tools’ tab, select ‘Application Options’ icon, when the dialog box appears, select the ‘Sketch’ tab. Near the bottom select ‘Edit dimension when created’. Now when in sketch mode and you place a dimension the Edit Dimension dialog will appear automatically.

There are actually two types of circles that Inventor has sketch tools for. The first one, center point circle we just described. The second, the Tangent Circle, requires that you pick three pieces of existing geometry to create a circle tangent to all three. You will see an arrow pointing down just below the circle tool, and if you click on that arrow, the icon for Tangent Circle will appear. If the geometry that you select is well defined (constrained) then you will not be required to place any dimensions for the size of the circle.

In the next Episodes we will start to look at some of the other sketch tools, and we will start to explore the concept of constraints.

Tod