Trouble Creating a Shell with a Loft

[Zoltan3D]

Hello all,

First, why my post disapeared here, but I can only see them in my subscriptions ?

I absolutly love Fusion, but I had today my first problem that I can't solve ..

I made a 3D shape, by lofting a cube to an other cube with 4 rails, works great

after that, I make a projection of a line onto the body, at the 2 en of the model, I made 2 circle that I want to use to loft cut the first body, I used the projected line as a centerline to follow

But every time I try, it make an error, I tried every options i see but he dont want to cut the body (only cut straight if I don't choose a centerline....

Here is the screenshot, it's easier to understand and I also add the file here you can check them

Thanks a lot if somebody find a solution

[SaeedHamza]

Your path is made of 3 lines, and a center line needs to be a continuous line to work

But according to what I see, you can use a sweep with a taper angle to get what you desire

Regards

[lichtzeichenanlage]

I do have more or less the same problem. I haven't finished to implement the hints from the video, but perhaps it helps to fix the shell issues in your example, too.

[beresfordromeo]

Could you please share your file. This is not something I have seen before so it would be great to take a look. Edit (ooops didn't see that)

[laughingcreek · Accepted solution]

When you used "project to surface" to create your centerline rail, you left the project type set to "closest."  It needs to be "along vector" to work right for this operation.  see screen cast.

Also, if you change the end conditions on your first loft to "g3", you'll get a smoother result.  I showed that at the end of screen cast. (creating some errors along the way, the yellow in the time line.  need to fix that.

[beresfordromeo]

Hi @laughingcreek

Thanks for the valuable information above.

I wonder if you would mind explaining the following...

Why the closest point projection onto a surface is not necessarily continuous compared to an along vector projection?

How does closest point differ from along vector.

In which scenarios is it better to use closest point as opposed to along vector?

Any help on this would be greatly appreciated.

[laughingcreek]

"Why the closest point projection onto a surface is not necessarily continuous compared to an along vector projection?"

because closest point projection can cause kinks  (ie not g1 or g2) in the line at face transitions.  As you found, rails need to be smooth along their length for loft to work.  These kinks can exist on a very small level, to small to directly see, and still mess up loft.

"How does closest point differ from along vector."

closet point literally projects to the closest point on a face.  this can cause the line to be warped when compared to the original curve.  along vector projects perpendicular to what ever plane is picked as the vector direction.

"In which scenarios is it better to use closest point as opposed to along vector?"

 I almost always use along vector.  I have used closest point when I had a 3d line in circulating a body, in order to get a line all the way around the body.  but even then I found better ways to achieve the desired result.  Some curves won't even project with closest point.

Here's a screen cast of some simple shapes projected to a half cylinder.  You can see the difference in the results using the 2 different types of project.  Along vector is much more predictable.

[beresfordromeo]

Thanks @laughingcreek for taking the time to do that. I really appreciate it.

So I spent a while messing around with 'closect point' projection and I have come up with the following conclusion.

I created a circle on a plane at x distance from the origin, created another plane tangent to face at point using the cylinder as the face and the centre point of the circle as the point then constructed a midplane between the x distance plane and the tangent plane. 

I then projected the circle into sketches on the midplane and tangent plane and projected all three of these circles onto the surface of the cylinder. This confused me a bit at first because I was expecting to see a definitive vector for the projection. I didn't so I also added inscribed polygons to the circles I was projecting.

So firstly it would seem that the projection of lines and curves to a surface involves using the vertex geometry of a curve and joining these with a line. That is to say that all circles (if not all lines and curves) are made from straight lines drawn in 2D or 3D space between vertices and refreshed as we orbit and move around the model.

A 2D (sketched) circle for instance is actually a polygon with n number of segments. When that circle is projected onto a surface using closest point projection, Fusion uses a line from each of the vertices (the intersection of these segments) to the closest point on the surface as a vector to plot a new point at the intersection of the surface. Fusion then joins those 'surface' vertices up with a line that is 3D in nature.

I really don't know if it is useful for anyone to know this but it may be relevant one day. Mind you I could be completely wrong about all of this so this could just be misinformation so any thoughts you or anyone else has on this would be great. I am hoping understanding this will help me to find a use for closest point projection in the future. Thanks again.