topic Re: Symmetry tool in Fusion Support Forum

Symmetry tool

gamelife4dns — Sun, 04 Apr 2021 21:49:15 GMT

Wishing for a symmetry tool sometimes.

We all know the mirror tool, either in sketches or modeling. But they lack symmetry references.
For sketch we should be able to select a point/vertex of symmetry, not only an axis.

While modeling bodies we should be able to select a point/vertex, or an axis, not only a plane.

I think a workaround could be using 2 or 3 times the mirror tool to achieve the desired result, but it should be a native one step feature. It is more intuitive.

May I suggest it for a future release ?

Thanks.

Steve

Re: Symmetry tool

TheCADWhisperer — Mon, 05 Apr 2021 10:47:03 GMT

There are an infinite number of possible solutions to symmetry about a point.

Can you Attach an example file that illustrates your point (pun intended)?

Re: Symmetry tool

gamelife4dns — Mon, 05 Apr 2021 11:44:38 GMT

For example, on a sketch (2D world), symmetry against one point is like making 2x "mirror" against 2 perpendicular lines/axes. The symmetry point is the intersection of the 2 lines.

Similarly, the symmetry of a body against one point is like making 3x "mirror" against 3 perpendicular planes. The symmetry point is the intersection of the 3 planes. The solution is unique AFAIK.

I attached a very basic f3d that mimics symmetry on a sketch (2x mirror), and with a body (3x mirror).

Here is a simple math example. Assume a Point at location [1, 1, 1].

Its symmetry against Plane [Y, Z] is [-1, 1, 1] (this can be done with Fusion 360).

Its symmetry against Axis [Z] is [-1, -1, 1] (can't at once).

Its symmetry against Point [0,0,0] is [-1, -1, -1] (can't at once).

Thanks.

Re: Symmetry tool

TheCADWhisperer — Mon, 05 Apr 2021 12:58:36 GMT

@gamelife4dns wrote:
While modeling bodies we should be able to select a point/vertex...

I am still confused how there can be a unique solution about a point/vertex?

https://autode.sk/2R8DwBh

Re: Symmetry tool

gamelife4dns — Mon, 05 Apr 2021 16:26:51 GMT

I feel you didn't look carefully at my F3D file.
I saw your update and screencast, you removed the sequence of mirror features that "mimics" the result of a symmetry point.

Please see a math explanation about symmetry point, I think it's quite well explained here :

https://www.mathsisfun.com/geometry/symmetry-point.html

On Fusion 360, think about a propeller with 2 blades. How would you make it ? (you are NOT allowed to use the circular pattern).
I uploaded an updated F3D with a component called Propeller. It contains 4 bodies, the main blade, and 3 blade copies :

-a copy using a "symmetry plane",

-a copy using a "symmetry axis",

-a copy using a "symmetry point".

I hope it's more clear now.

(A mathematician should jump on the discussion, it should be obvious for him 😉)

Steve

Re: Symmetry tool

TrippyLighting — Mon, 05 Apr 2021 18:40:22 GMT

@gamelife4dns wrote:

(you are NOT allowed to use the circular pattern).

And why would that be?

Re: Symmetry tool

gamelife4dns — Mon, 05 Apr 2021 19:41:16 GMT

As an exercise, just asking another way to find a solution 😉

I'm just trying to show that extending the "mirror" feature to a more generic "symmetric" feature would be helpful.

And, obviously, a symmetry point or axis or plane is a matrix transformation and has a unique result. It is a college math course.

Steve

Re: Symmetry tool

hammerquill — Thu, 30 May 2024 09:25:24 GMT

Since people who don't understand point symmetry keep replying in threads like this, and since point symmetry is an extremely useful functionality sadly lacking from Fusion, here's what point symmetry means. It is not a vague or handwavy thing. It is rigorously defined.

To begin with, let's consider only 2D, and say that we want to make something point symmetric about the origin. That means that for every point in the original sketch object (I mean mathematical point, not Fusion Sketch Point), draw a line segment to the origin. Then continue an equal distance beyond the origin, and place a new point there. Do this for every mathematical point in the original sketch object. It creates a new object which is reflected in two axes at once. The exact same process is how you define point symmetry in three or more dimensions. The math is very easy, and though I guess it would require some serious processing when applied to large parts, in the sketch environment it's just silly not to have it.

Given the painful process necessary to do this at the moment in Fusion, especially in a complicated sketch, a point symmetry tool would be extremely helpful. I need this often enough to have gone searching for it several times. There is a feature request for it here: https://forums.autodesk.com/t5/fusion-360-ideastation-archived/point-symmetry-in-sketches-and-3d-workspace/idi-p/9308156