Symmetry Collapse Sketch Bug

[glrra30]

Sketching on face of body.  Use Symmetry to center another line between an edge and another dimensioned line.

Now add another line parallel to the lines with symmetry.  Symmetry collapses and dimension changes.

If you delete the new line the symmetry returns.  Was having this issue in another model, but was sadly easy to recreate the issue in a new Design.

[g-andresen]

Hi,

I have removed all lines and recreated them according to your scheme, and the described error does not occur.

günther

[glrra30]

Same order of operations?  All the lines on the right, then the symmetry, the line on the left last?

I'm on a Mac, maybe it's Mac-specific?

[g-andresen]

Hi,

did you remove the actions once and repeated them completely in the same way?

günther

[glrra30]

Deleted all the elements in the Sketch, repeated the actions.  Same behavior.

If I wait until after drawing the line on the far left, then apply the Symmetry to the three lines on the right it doesn't collapse.  That doesn't make it not a bug.  You should be able to add an element to a sketch without the previously fully constrained elements failing.

[davebYYPCU]

Repeatable on a Windows machine too.

Might help...

[g-andresen]

Hi,

that´s what I see

günther

[glrra30]

To recreate issue: draw line at 75mm from right first, dimension, then draw center line between far right  and line at 75mm.  Add Symmetry.  Sketch should be full constrained at this point with projected surface boundary, one dimension, and symmetry constraint.  Now add line on far left.  Collapse . . . .

This is different than your video above where you delete the line at 75mm from right . . . .

[g-andresen]

Hi,

symetry in clean sketch

günther

[glrra30]

@g-andresen, evidently the horizontal centerline is necessary to trigger the problem.

1)New Sketch on face.

2)  Project edges of face.

3) Vertical line @ 75mm from right. (trim as needed)

4) Dimension (3) to 75mm

4) Horizontal line from mid-point (3) to mid-point far right.

5) Vertical Centerline (trim as needed)

6) Symmetry (3) & (5)

7) Draw vertical line to left of (3) . . . . collapse

[g-andresen]

Hi,

In the meantime, I tested different scenarios and found that the behavior shows up in other sketches as well.
Result:
1. the error does not always occur
2. it occurs only in combination with projected sketch elements, but not with sketches without projections.
3. the symmetry line "seems" not to play a role.
4. moving the outer line activates or deactivates the effect.

I will report when I have new insights.

günther

[davebYYPCU]

For me that’s a bug, it’s repeatable.  @jeff_strater  Should not happen, but it does.

Those of us been here a while use other constraints to get it done,  

Don’t hold your breath waiting for sketch engine fixes.  

Avoid symmetry and mirrors if there are more robust methods.

constrain the middle line to the centre of the construction line.

Might help….

[g-andresen]

Hi,

Currently it looks to me that the described behavior only occurs when the symmetry contains a projected line.

If you replace it with an independent line or remove the link, the error does not occur.

günther