topic How do I thicken this? in Fusion Design, Validate & Document Forum

How do I thicken this?

ripley98 — Tue, 30 Nov 2021 00:08:02 GMT

Hello, I am trying to design a rc boat hull for fun. I have found another forum that is similar to this but my design is slightly different and I am having issues thickening my surface. I feel like it is an issue with sweeping to a point but it is over my head. Any input is greatly appreciated.

Re: How do I thicken this?

jeff_strater — Tue, 30 Nov 2021 01:02:52 GMT

it looks as if you have deleted the feature that created these surfaces, which is not generally a good idea. It would be interesting to see what you did there, might give us some clues as to the problem. It looks like you might have used Loft. Is that the case?

Certainly, the tip of the boat is probably the source of the problem. Thicken does not give much feedback, so I deleted the Delete Face feature, and Stitched everything together into a solid, so I could try Shell on it. Shell and Thicken share a lot of the same algorithms, so this can be useful. Shell does give feedback, and shows this face as the culprit:

Next, I turned on a Gaussian curvature map analysis, to show the surface curvature. Areas of high curvature are also a problem for Thicken/Shell. It shows quite a lot of areas of high curvature:

Which is why it would be good to understand how this was created. Those areas of high curvature are usually indicators of problems.

It is also useful to turn on curvature combs for the sketch curves. You can see a few problems there (the long lines indicate areas of high curvature). The less curvature you can get, the better off you will be with Thicken/Shell.

Re: How do I thicken this?

ripley98 — Tue, 30 Nov 2021 01:25:00 GMT

Thank you so much for your help! I am completely new to cad so please forgive me if I add confusion. Right now, I am just trying to understand the problem of both the shell and thicken command for my method. I uploaded an earlier version of this model which is solid based. It was indeed constructed with a loft based on a right view sketch and then a series of front plane sketches. Again, I apologize if I am adding confusion, you already have helped immensely. I also attached a front pic of the real boat that I am trying to base this one off of for a reference.

Re: How do I thicken this?

TrippyLighting — Tue, 30 Nov 2021 02:46:55 GMT

@ripley98 wrote:

Thank you so much for your help! I am completely new to cad ...

In that case, this isn't a good project to start with. Have you gone though any of the courses here?

Anyway, lofting creates NURBS surfaces. In that sharp point you lofted into, all CV (control vertices) collapse into one point. THE weights associated with those control points mathematically approach infinity, so the software has to approximate (or crash). That approximation causes the surface curvature to be very rough and the4t is what prevents offsetting surfaces, thickening, and shelling.

Your loft technique is somewhat questionable. I personally would use 3-degree control point splines (with 4 control points, not more, not less) for this, and perhaps even in 3D (not flat on a sketch plane. That way you only need a starting profile and the point (you do need the point). Then you use the control point splines as rails.

Then we trim the tip off (we keep it for later use) and shell. Then we re-join the tip. I am assuming this will be 3D printed.

Re: How do I thicken this?

TrippyLighting — Tue, 30 Nov 2021 02:49:02 GMT

Did you post this project on the Fuiosn 360 Facebook group?

Re: How do I thicken this?

ripley98 — Tue, 30 Nov 2021 15:21:56 GMT

Thanks for the input and explanation! I will give the training videos a look also. I am taking courses on Udemy, but always look for more training.
So the 3-control point splines will be used as the guide rails and one sketch profile will be used for the loft. In my previous attempts, I lofted to a point in the spline (guide rail). Is this a problem or should I create a plane and insert a point to loft to? Also did not know there was a facebook group, will certainly give that a look! Thanks.

Re: How do I thicken this?

wersy — Tue, 30 Nov 2021 16:11:47 GMT

Creating a hull from frames in CAD is always problematic. And the more frames you use, the worse it gets, because you hardly have any exact frames available. A loft with inaccurate frames will create dents and bumps on the surface. The surface becomes smoothest with an initial profile, an end profile and a profile in the middle.
And as @TrippyLighting mentioned, you need rails for a good loft.

Better is to create the outline of a hull with splines and use the formers in between only for orientation.
These splines are created from the intersection of the respective spline from the side view and the corresponding spline from the top view. This means that each spline must be drawn once in the top view and once in the side view.

This way you get an intersection curve:

So, besides the central deck line and the keel line, you get 3 more rails:

If it is accurate enough, it is enough to create a loft with only one profile.

The tip of the bow is still too pointed to shell. As @TrippyLighting said "Then we trim the tip off".

This way, you can shell it 0.5 mm.

BTW, if you want to print it you do not need to shell it, the slicer can do it as well.