Sometimes, I define the dimensions of the drawing, and most of the entities turn black. Yet, however, some remain blue.
If a line is still blue, then it's position isn't fully defined, even if you've dimensioned it's length. When that happens it's often helpful to grab the line, or an end of it, and try to drag it. That will usually let you know what dimension or relation needs to be added. Neglecting to link sketch entities to the origin, with dimensions or relations, is commonly overlooked by new users.
I teach that trick to everyone that asks me "but what's wrong with it then? It looks perfectly defined." My reply: "just drag a few points until you're able to break the sketch."
It could also be in your settings, or layers in in a drawing.
Also it can depend on how the dimension is created. Here is the same square with the same constraints. In the first one the dimensions were made at the corner points. The second one the dimensions were made to the lines.
Biggest mistake when starting out:
Relative to Origin.
This gets missed a lot for new designers you can have fully defined geometry, except no relation to the origin.
Simple example is a 2 x 2 square but nothing ties it to the origin so all lines remain undefined.(I don't use blue and black lines as our materials have blue and black as common appearances).
If the line is blue that means it is NOT fully define, you can right click and click fully define .it will do it for you automatically.
Yes, you can use the inbuilt 'fully define tool' no problem at all, but I believe personally (especially for a beginner) that it would be a better practice to learn to manually fully define your sketches so that you know where they are defined from and also that your dimensions are indeed correct, rather than just let SolidWorks populate the sketch with some figures and move on............. Just a personal preference!
Surely it doesn't matter if it's a single entity, or a group of entities, if they're blue, they undefined. The perfectly dimensioned group of lines, though constrained to each other, still have the ability to move in an uncontrolled manner within the model giving it the ability to wreak havoc in the over-all geometry = undefined.
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