Under defined sketches

Usually, the starting point of a sketch is under defined. Under defined sketches have parts of them that are loose or lack proper definition; for example, a line without a specific length. To find out more about under defined sketches, we'll examine the following sketch. We will use the MMGS measurement system for this exercise. We have indicated the lines and points with the letters L and P for reference:

Take some time to sketch the preceding image and examine it. From this sketch, we can see the following:

• Note that, in your SOLIDWORKS canvas, P1 and L1 are black in color. Black colors indicate that those parts are fully defined. To test this further, click and hold P1 or L1 and try to move the mouse. You will notice that the sketch doesn't move. This is an indication that that part of the sketch is fully defined.

• The other parts of the sketch (P2, P3, L2, and L3) are blue in color. This indicates that those parts haven't been defined yet. To test this, click and hold any of those parts and move the mouse. You will notice that those sketch parts move around the canvas. If any part of the sketch is blue, the sketch will be labeled as Under Defined at the bottom of the SOLIDWORKS interface, as shown in the following screenshot:

We will always try to make our sketches fully defined. To fully define a sketch, we can simply add more dimensions and/or relations to turn the blue parts black.

To find out which parts of the sketch need definition, we can click and hold on any of the blue parts and move them. The resulting movement tells us which parts need definition. For example, if we hold and move P2 left and right, we will notice that L1 changes in length. This indicates that we can define P2 by setting a dimension for L1 (or between P1 and P2), as shown in the following image. After defining the length, we will notice more lines turned black. Now, if we click on P2 and try to move it, it will be fixed:

We can do the same movement test for L3 and P3 and decide what elements of the sketch we can define further.