lofting tangent to plane error

[Anonymous]

I seem to be getting this, can you tell me what is wrong here please?  I have selected the gunwale OK but this drags the centreline out, when I pick the centre line I get this error pop up.

[TrippyLighting]

You are using way too many control points on your splines.

You are using too many rails.

You are using too many profiles.

Less is more as it pertains to lofting.

If you keep that in mind, Fusion 360 will loft happily most of the time with acceptable results.

[Anonymous]

Uh but I am not getting the shape I need, so I need to use multiple rails

[Anonymous]

The splines are curved to fit the original frames, I have used as few as I could to get the shape fit I need.

[Anonymous]

Looks like googling eventually gave me the answer, I un-clicked "chain selection"  seems to work OK.

[TrippyLighting]

You can argue with me, or listen and learn. The choice is yours!

[lichtzeichenanlage]

"Unfortunately" @TrippyLighting is right 😉 For me this lofting stuff is still hard and drives me crazy. Perhaps this video helps you:  Fusion 360: How to design a Wooden Boat - Part01

PS: @TrippyLighting Pls don't get me wrong.

[Anonymous]

This isnt an argument. The thing is i need to achieve a certian shape this isnt 'free form' drawing or sketch where "this looks nice it will do". The idea is to try and get reasonably close to the original hull shape.   Now in effect you are telling me that lofting in fusion360 isnt really up to doing this, so, yes Ok I'll look for a product that can do it or wait a year or two until fusion360 has improved.

So this isnt an argument it looks more like you tell me Fusion360 isnt up to the job I need it to do, that is fine.

[Anonymous]

Thanks I think I have probably have watched it.   The point is really if Fusion360 cant do this, Ok just saying so is fine, I'll wait a year or so til it improves or try another piece of software.  Or if my technique is wrong, OK, but simply telling me "you are not doing it right", isnt much help.

[lichtzeichenanlage]

@Anonymous: I had the same feelings in my thread. And not sure it is because I'm a beginner or because F360 just works different / unexpected. But the truth is, that you can achieve an accurate design with less profiles and rails. It's a pill I had to swallow and I didn't liked it 😉 That's the reason why I've quoted my unfortunately.  

[Anonymous]

Hmmm, further back along the hull from frame 7 to 2 I am down to 3 rails and the shape if fine.   The problem is really the bows look terrible from frame 2 to 0 unless I add more rails. 

[TrippyLighting]

No, the point is that what you are trying to do is simply the wrong workflow to achieve your goal. It is a mistake that many new users make.

You cannot simply take a boat plan and assume you can re-create surface from the information presented on it. This is not how boats are designed digitally.

This article about the dirty little secret of NURBS explains some of the pitfalls many new users don't understand because they have been hidden by all too intuitive user interfaces that lull unassuming users into believing that something can be achieve that can actually not been done.

If you check the curvature of a 3-degree spline (all splines in Fusion 360 and many other CAD products are 3 degree) that has too many control points you'l simply see that it looks pretty horrible. If you create a surface from that form of spline it will simply have the same problems, likely even worse.

This is easy to check with the the main tools in the Inspect menu, the curvature comb, the zebra stripe analysis and the curvature map.

As Fusion 360 uses 3 degree splines the idea is to limit the number of control points on these splines to achieve smoother curvature and to avoid problems resulting from bad curvature.

While there are limits how far you can go in Fusion 360 with surfacing, currently the limit is your level of knowledge that area. You will need have some more knowledge if you want to start using a higher end product, which in this case clearly would be Autodesk Alias. However, I've been told by experiences Alias users (Other EE's EE that have usesd and tought Alias) for my own projects that are starting to venture into Class-A surfacing to say away from Alias as it apparently is quite a beast to drive.