How do I scale a primitive object from it's center?
Hi @Anonymous
Thanks for posting! The current method with which to scale a primitive object from its center is to create a center point using sketch geometry and select it. While there are some advantages to selecting a point each time (if you need to keep certain edges lined up in an assembly but increase the size of one body for example), I think a good addition to the Scale dialogue box could be a "Scale about Center of Mass" flag or the ability to select a marked Center of Mass as the point for the body to be scaled from.
I'd like to hear your ideas for how this tool should work at the Fusion 360 Ideastation, where enthusiasts can submit and vote on suggestions for future features and improvements to the software! A similar idea can be found here - please give it a vote and let me know if you have any questions.
I will be honest here. This is not high on the priority list. I would not expect to see it implemented any time in the near future. No one is saying that this would not be useful, it would. But, there are lots of higher-priority problems that need to be addressed first. Sorry to bear bad news, but thought it was better not to set false expectations.
Jeff Strater
Engineering Director
I am an artist not an engineer which means that both my workflow and the objects I make are more organic than the typical use case for Fusion 360. I've been creating sculptural forms digitally for over a decade and I realize that because I am often trying to force software to create forms it was not intended to create that I am at a disadvantage and have little room to complain when it doesn't work the way I want it to. I keep trying to push the medium though because that's what artists do.
Upon further reflection I also realize that most of the software I attribute center mass scaling to are mesh editing software like Meshmixer, Mudbox, Z brush etc. which is are not directly comparable to Fusion. This functionality, however, is so ubiquitous that it is what I consider "normal" when thinking about scaling functions and I am still baffled at the lack of this functionality in Fusion and the need to explain its utility. I do understand why the scaling function works the way it does in Fusion, I just don't understand why it doesn't work the way I have described also. Being able to create a reference point automatically at the center of any body, the center of any face, and the center of any sketch profile would make scaling and orienting portions of complex forms to one another much easier. Meshmixer can do this using pivots oriented to bounding box volumes and facegroups, for example.
The included image shows a relatively straightforward 3D printable model I created last week which I think is a good example of a common circumstance in which scaling from center is useful. This model was created using a calibrated canvas reference and all the bodies are thus created in place relative to one another. I don't think BORN techniques are applicable here, but I could be wrong and I will do more investigating of that practice.
The grip body is a lofted surface with multiple rails, converted to solid, and it nests inside the ovoid body. The grip is then copied, scaled up to create tolerance for assembly after printing, and used as a boolean tool to cut the indentation into the main form. When the scaling portion of this operation cannot be performed such that the body expands equally away from the center, the hole that is cut is not in the correct location, nor proportioned properly to the original body that needs to fit into that hole. Since the top surface of the grip is actually flat the solution for this part was to create a sketch on that face, project the profile of that face, draw a line down the center, and place a point at the center of that line and use that point to reference the scaling. This works well for this part because I actually don't want the hole to be deeper on the Z axis, but the four other parts in this design requiring this process were much more difficult to reference a sketch plane to for this purpose. As I said, those extra steps are cumbersome and create additional clutter in the browser and timeline.
@mcottrellart wrote:... The grip body is a lofted surface with multiple rails, converted to solid, and it nests inside the ovoid body. The grip is then copied, scaled up to create tolerance for assembly after printing, and used as a boolean tool to cut the indentation into the main form.
Even if scale around bounding box center of mass was possible I don't think it would be the right tool for what you describe above. Just to show the point I've scaled the black shape up 10% around its CM:
What you described should be done by Surface Offset.
@mcottrellart wrote:... I usually add features that can only be applied to solid bodies before the boolean, and offset surface isn't useful for bodies that were never surfaces to begin with...
@mcottrellart Offset Face is the tool to offset faces of a solid bodies directly. Also Surface Offset is still useful for solid bodies, you only need to do further work to make solid out of it.
... the profiles and bodies I usually use are much more symmetrical than your drawing, which minimizes this issue somewhat...
Symmetry in general doesn't minimize that problem, being close to sphere does. Only for sphere scaling around center produces uniform offset because every surface point is at equal distance from the center.
... We were also discussing scaling from the center of the body, not just the center of the face...
I had drawn a 2D shape just for simplicity but the point applies to 3D as well. Here is a simple example to show that scaling around CM of a 3D solid body is not useful for your case, and Offset Face is the right tool:
