Pulling / Matching Symmetric Form to Sketch

[werksmini]

Hello,

I'm trying to pull some vertices of a form to match that of a sketch. This is a helmet and has a symmetry about the center. When I use the match function. I loose the symmetry. I tried to "pin" the vertexes that are on the line of symmetry to points on a sketch, but that didn't hold. You also can't freeze a point, just a face it seems. 

Any ideas? Thanks!

https://a360.co/2McZXQZ

[jeff_strater]

I believe you are correct.  Match Edge will break symmetry.  There is just no way to satisfy both requirements at the same time.  If you believe that after the Match, your body is still symmetric, you can always re-apply symmetry.  That may move some vertices, though.

and yes, Freeze only applies to faces or edges, not individual vertices

[chrisplyler]

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@jeff_strater wrote:

I believe you are correct.  Match Edge will break symmetry.  There is just no way to satisfy both requirements at the same time.

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Interesting. I don't work with forms, but...

...Why can't you Match a vertex point on one side of the symmetry, and have the other side move into a symmetrical place?

[jeff_strater]

you are right, Fusion is a bit lazy.  There are certainly cases where Match could be made to work with symmetry.  But, detecting those cases is a bit difficult, so, because it can't be made to work in the general case, it defaults to just removing the symmetry constraint.

[werksmini]

Is there another way to join symmetric forms to parametric bodies or sketches? I've tried killing the symmetry, matching the form to the sketch, and then trying to reassign the symmetry but I'm unable to reestablish the symmetry. Also, it seems that once you match something it does not hold this action. For example, you match this edge to sketch, the next move you make can freely disconnect the two. 

I also tried pulling each point of the vertex to a sketch point, which works, but doesn't hug the sketched circle with out a lot of fiddling. 

Any ideas? I have to assume this comes up fairly often. Thanks!

[TrippyLighting]

No, this actually does not come up very often at all.

One thing that you are probably not aware of is that you cannot just match any T-Spline to an arbitrarily curved edge.

Just as with a spline the only controls Fusion 360 has at its disposal is to modify the location size and orientation of the spline handles, T-Spline handles in this case. There is a limit also what you can match with that.

Your helmet might simply not have enough geometry to achieve a good match so it needs to be subdivided more.

Can you share your model ?

[werksmini]

Thanks for the the feedback Peter. File attached. 

If you were looking to make a mirrored shape like this fit a parametric body, how would you go about it? The best I can do at this point is to manually fit points of lower edge to the existing body/sketch. This is fine and works well enough, i'm just curious about what others might do in a similar situation to make a workflow like this more precise and efficient. 

Thanks again for all the help, I appreciate it.