topic Re: Issue with maintaining curvature continuity between lofts in Fusion Support Forum

Issue with maintaining curvature continuity between lofts

abbgray18 — Fri, 10 Dec 2021 15:33:02 GMT

Hello.

I am quite new to fusion 360 and I have encountered a problem on a project I have been working on where I need smooth, continuous curvature between a relatively flat section and a section that converges to a point, (as shown in the screenshot). I have tried many different ways to reduce strain on the loft tool at this section by creating the surface in smaller pieces but each way seems to cause just as many issues with obvious seams if I don't connect the lofts with G2 continuity or I get unwanted rippling on the surface when connected with G2. I assume I'm just doing everything completely wrong from a lack of knowledge about fusion 360.
If anyone, who is more experienced on the matter knows of a way to make it appear smoother with a better surface quality that would be greatly appreciated. The sections in question are attached in the file.

Thanks

Re: Issue with maintaining curvature continuity between lofts

TrippyLighting — Fri, 10 Dec 2021 22:52:13 GMT

One short timeline. 3 mistakes 😉

1. Don't use a 3D sketch if it can be sketched on 2D sketches.

2. None of the spline segments have a G2 curvature continuity constraint applied.

3. A triangular loft will almost always result in curvature problems.

Re: Issue with maintaining curvature continuity between lofts

abbgray18 — Sat, 11 Dec 2021 19:42:33 GMT

Thanks for the response. I'll try to incorporate those tips when redoing the design.

Re: Issue with maintaining curvature continuity between lofts

TrippyLighting — Sun, 12 Dec 2021 11:48:47 GMT

If you can explain with images and words what you want to design, I can provide more detailed help.

Re: Issue with maintaining curvature continuity between lofts

abbgray18 — Tue, 14 Dec 2021 21:54:21 GMT

Hi.

Sorry for the delay in replying.

I was attempting to make a 3d printable sneaker sole which has parts that cut in about half way along each side. I was able to get a fairly smooth surface quality on the majority of the sole but once I got to the parts that cut in, I couldn't find a way that gave a clean result due to the lofted sections converging to a sharp point and attempting to connect the sections with G2 curvature continuity leads to multiple surface errors.
I was trying to see if there was another method to create these parts which didn't have so many obvious surface imperfections but I haven't had much luck so far.

I assume there must be a better way to create these features in fusion 360, that I haven't come across yet. If there is a way to create these sections so they retain the same, or similar, shape as the ones currently on the sole and so that it has a smoother transition, that would be great.

Thanks

Re: Issue with maintaining curvature continuity between lofts

TrippyLighting — Tue, 14 Dec 2021 22:37:16 GMT

If smooth curvature is your goal, the first thing you need to focus on is creating smooth curves. This isn't smooth:

It might not matter that much for a sneaker, but if you already go through all that surfacing and lofting effort then try using fewer curves - two should be OK, and minimize the number of spline points. 4 points per curve should be all that is needed. 5 max. Work with the tangent handles.

Re: Issue with maintaining curvature continuity between lofts

abbgray18 — Thu, 16 Dec 2021 20:02:09 GMT

OK thanks.

I will redo those sketches so they are smoother. Would a smoother sketch also fix the curvature continuity between these conjoined lofted parts:

Or would I need to make it using a different method as when I 3D printed a test section there is still a visible seam between the changing curvature on these joining loft sections, even with G2 continuity, this seam also shows up on the actual 3D print.
Would it be possible to make it using a different tool in fusion 360 so that the seam is smoother and not so visible and therefore wouldn't show up on the actual print or is this method with the loft tool the only option for something that shape?

Thanks

Re: Issue with maintaining curvature continuity between lofts

TrippyLighting — Fri, 17 Dec 2021 00:38:06 GMT

@abbgray18 wrote:

OK thanks.

I will redo those sketches so they are smoother. Would a smoother sketch also fix the curvature continuity between these conjoined lofted parts:

Or would I need to make it using a different method as when I 3D printed a test section there is still a visible seam between the changing curvature on these joining loft sections, even with G2 continuity, this seam also shows up on the actual 3D print.
Would it be possible to make it using a different tool in fusion 360 so that the seam is smoother and not so visible and therefore wouldn't show up on the actual print or is this method with the loft tool the only option for something that shape?

Thanks

No, smoother curves will not help that particular detail It will simply eliminate 50% of the work in the design.

Then a bit nore forethought will eliminate another 25%.

You might have applied a G2 constraint when lofting, but you don't have G2 curvature continuity across that entire seam. The way you are modeling his is is technically not possible.

You have created a triangular loft. In the highlighted areas the NURBS control points collapse into a single point so your curvature collapses as well and G2 mathematically cannot be maintained.

You need to change your modeling approach for that area.

Re: Issue with maintaining curvature continuity between lofts

abbgray18 — Sun, 19 Dec 2021 23:24:36 GMT

OK, thanks for all the help. I will redesign that part so it hopefully won't have as many errors next time 😁