Why Is This Sketch Marked As Fully Defined?

[Inspections_JCH]

In this file there is one horizontal line that has both end points locked in place. At that point, the sketch is identified as fully defined.  I then constructed a second line that is constrained to the midpoint of the first line and the other end is locked at a point in space that cannot be moved.

The sketch is identified as fully defined as shown in this image that is attached here. And still the sketch has a red padlock icon on it. Now I take the end of the second line that is constrained to the midpoint and slide it along the first line. What am I supposed to believe about the midpoint constraint, or the sketch icon that says this is fully defined sketch?

Why is line number two loose at one end?  Is This A Fully Defined Sketch? 

[HughesTooling]

Fusion doesn't seem to like the just having the endpoints fixed. If you make the line fixed as well then try dragging the angled line it will snap to the midpoint correctly.

[Inspections_JCH]

And.... how many other constraints cannot be trusted. Or, is the center point constraint one that uses 'fuzzy logic"? And is the red lock icon on the sketch equally unreliable?

I see many Autodesk tutorials that start by sketching a line from the center point of another line as though that can be trusted. Here is a demonstration that this constraint is unreliable.

At best it is poorly described and its functionality is undocumented.

[Inspections_JCH]

 So what is the definition of the midpoint constraint? Is it just SOMEWHERE OR ANYWHERE on the line. Moving the line does not delete the constraint.

[HughesTooling]

There is a bug here and it's down to the fixed constraints at each end of the horizontal line, if you make the line and the endpoints fixed it seems to work. Personally I'd never have a fixed constraint in any sketch I make and if you dimension this sketch it works first time no problems. @jeff_strater  Can you take a look at the sketch in the first post.

Mark

[TheCADWhisperer]

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@HughesTooling wrote:

Personally I'd never have a fixed constraint in any sketch I make and...

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Ditto!

[jeff_strater]

yes, this is a bug.  The reason it has not been identified before is that most people do not Fix points only to get them to constrain a line.  As mentioned here, dimensioning the points from the sketch origin, or additionally, fixing the line itself works.  I will create a bug for this.

[edit] the Fusion bug is FUS-93268

[Inspections_JCH]

I think most people agree that they do not use a fixed constraint. I have never seen it mentioned in tutorials. It makes me wonder if it is only used as a last resort when other constraints seem to not addressing the issue.

[jeff_strater]

Here is what I did for that sketch to prevent using Fixed: