How do I un-constrain elements and references?

[laroot]

Constraints continue to be the part that I understand the least and that create most of my current problems.  I want to be able to leave each sketch unconstrained so that I can reference points as the beginning of my next sketch.  I don't want to fully constrain the sketches until the final component and sketch where the concept will be completely developed.  I'd then like to have the dimensions in my last sketch be reflected in the parent sketches.  This would avoid iteratively revisiting and amending the earlier drawings.  But I cannot make that work.

Does Fusion 360 deem an element fully constrained by a reference to an element that is not fully constrained in another sketch? 

If so, is there a setting by which I could prevent that reference from fully constraining the derived sketch? 

If not, how do I avoid putting all of my information into a single, unreadable sketch?

To demonstrate why I’m confused, I created a component, created a sketch, and drew an arbitrary rectangle using the origin as a vertex. 

Why are the sides on the x and y axes fully constrained when no dimensions have been assigned to them?

Given that a rectangle is, by definition, a parallelogram with right angles, and given that Fusion deems the lines on the axes to be fully constrained, why are the two opposite sides not also fully constrained?

I drew another arbitrary rectangle that did not include the origin as a vertex.  As I expected, none of the sides are fully constrained.  But, just as when the origin is a vertex, adding dimensions to locate one vertex made the attached sides fully constrained even though their lengths are not defined. 

Why?

I then created a second component, created a sketch, and referenced two rectangles off of the vertices in the first sketch.

Why are both derived rectangles deemed fully constrained when neither referenced rectangle is? 

I would sincerely appreciate any suggestions or recommendations that you can offer.

Very respectfully,
Larry

[SaeedHamza]

Hi,

Constrains are automatically created in fusion when ever you use a reference to create a sketch, not to mention that fixed shapes in sketch menu are created with constrains automatically

and same goes for dimensions, as they define a constrain between lines when ever you create them, as you can fully constrain a sketch by using only dimensions

check this screencast please for better understanding

https://knowledge.autodesk.com/community/screencast/97d91f2b-18b3-444d-a6d0-2437fb75fbbf

and here is this tutorial to help you even more to understand the nature of dimensions

https://www.youtube.com/watch?v=19KzHow1EpE&t=193s

Regards, Saeed

[FrankCao · Accepted solution]

Hi laroot,

Thanks for the questions for sketch constraints. I am afraid I cannot answer all of the questions you have raised, but I will try answer some of them as follows:

1.Does Fusion 360 deem an element fully constrained by a reference to an element that is not fully constrained in another sketch? 

If you project the sketch curves from other sketch, then yes, the projected curves will be shown as purple and marked as fully constrained.  When we say fully constrained, we only mean the geometry in the current sketch is fixed. "Fixed" here has two meanings, for point, fixed means the position of the point is fixed. But for curve, fixed means ONLY the direction of the curve is fixed. A curve could have two endpoints that are not fixed, but the curve itself is still thought of as fully constrained. As projected curves are fixed curves(they cannot move inside current sketch), so they are deemed as fully constrained.

2. I created a component, created a sketch, and drew an arbitrary rectangle using the origin as a vertex. Why are the sides on the x and y axes fully constrained when no dimensions have been assigned to them?

If you draw a rectangle on the origin, then coincident constraint will be added between the corner of the rectangle and the sketch origin. In this case, the rectangle's two edges' directions are fixed with x and y axis. Like what I have mentioned above, the two edges will be marked as fully constrained because their directions are fixed.

3. Given that a rectangle is, by definition, a parallelogram with right angles, and given that Fusion deems the lines on the axes to be fully constrained, why are the two opposite sides not also fully constrained?

The other two sides are not fixed because their directions are not fixed. There are no other dimensions or constraints added to help fix the directions of them.

4. I drew another arbitrary rectangle that did not include the origin as a vertex.  As I expected, none of the sides are fully constrained.  But, just as when the origin is a vertex, adding dimensions to locate one vertex made the attached sides fully constrained even though their lengths are not defined. 

Same with above answers, adding dimension will make several curves' direction get fixed, so those curves are deemed as fully constrained although their lengths are not defined.

Thanks,
Frank

[laroot]

Thank you, Saeed.  Those were both helpful.  Larry

[laroot]

Thank you, Frank.

I'd not tried to change the lengths, only move the rectangle as a unit.  So I'd not noticed that the "fully constrained" black marking didn't indicate that the line was, in fact, fully constrained.  Arrgh.  But this is a really helpful piece of information.  I've had other models with an element was marked fully constrained but logic and constraint glyphs showed that it wasn't.  I wasted a LOT of time trying, unsuccessfully, to decode the models.  You've given me an important fact that I'd totally missed.

Very respectfully,

Larry