Create Loft Rail on Two Planes

[MaxHugen]

In creating a hydrofoil for a SailGP F50 catamaran, I've managed to get a few of the body sections made, this image shows them plus sketch "End Elevation" showing the general curve:

The bodies "Port Foil Mid 1" and "Port Foil Mid 2" both have a constant foil profile along a centre line.

Sketches 4 and 5 have a change in the foil profile, and become a bit wider.  I added a 3-point plane "Plane 4-5" to link those sketches as Rails in sketch "Profile 4-5",  which are OK on this plane.

But looking from the Left, these "rails" should also follow the curve of the "End Elevation" sketch", that is on the XZ plane as well as "Plane Profile 4-5".

Can anyone suggest how that could be done please?

[jeff_strater · Accepted solution]

not 100% sure I understand the complete requirements, but I think you need to make two different sets of curves tangent.  The problem is:  for splines, tangency can only occur at the endpoints.  My original thought was to do Include 3D Geometry" into "Profile 4-5", from the curve in "End Elevation", but unfortunately, the spline in "Profile 4-5" intersects that included curve in the middle.

I think I have an idea, and I'll record a screencast to illustrate...

[jeff_strater]

I'm not sure that this 100% satisfies what you are trying to do, but it might send you in the right direction.  In this screencast, I used Include 3D Geometry to include a model edge, then made the spline coincident with the end of that edge, and tangent as well (I had to remove some constraints to do that).

The resulting rail curve can be used with Loft:

[MaxHugen]

Hi Jeff.  After working right through the night figuring out how to draw this component, I think I made a mountain out of a mole hill.   I could have just said "draw a curved line on a plane, then turn it sideways 90° so it looks straight, and add more curvature in that view as well."

With 23 days of CAD experience I still find the Screencasts a bit hard to follow, but a bit later on I'll sit down and concentrate on it.

Cheers, Max

[MaxHugen]

Hey Jeff,  after watching your screencast many times over at 0.5 speed, and trying to follow you identically, I started to get the gist of what you were doing, and why.   Also found a post of yours, I think maybe 5 yrs old, pointing out that you can't drag a spline point when in 3D. That was helpful, I'd gotten into a knot over that!

Learnt a lot from the screencast, must get to know "Project / Include".  Setting a tangent from the other body was something I needed too.

Not quite there yet, would still like the Left view showing the bodies following the End Elevation sketch properly, but I need to revisit the previous bodies I did, they need some attention as I get to know more.  May also look at making the transition from one foil profile to another a bit less abrupt too.

Thanks for your pointers, I have plenty more to go on with now.  🙂

[jeff_strater]

thanks for the response, @MaxHugen .   Yes, screencasts from others can be hard to follow.  For some reason, screencast will not record my microphone, so there is no audio, which could help.

Glad that you are able to make some progress.  Yes, I understand that the real goal is to have the bodies follow that End Elevation sketch, but the problem I ran into of needing to be tangent to that curve in the middle got me stuck.  This is really a Fusion limitation, and an unfortunate one.  But, there are ways to make it work, I just got too lazy to try to dig into those.  Let us know how you are coming along with this...

[MaxHugen]

No worries mate.

I've gone down a rabbit hole and have started mucking things up. My fault, just don't know enough about F360, maybe not the ideal tool for doing all the 3D curvy bits I have to deal with.  Started getting odd things happen that I couldn't handle, like being unable to extend a line (in the End Elevation), adding a dimension to a sketch and later discover it's sitting way out in space when I switch to another view, instead of on the plane I was working on , etc.  Constraints also leave me struggling at times, as I can't sometimes tell what one point/line/curve is constrained to what.

Is it practical to to create one component, like I'm currently working on, in a separate project and then import it when it's satisfactory?   Or link it to this "master" one?  That would keep major components completely isolated as projects whilst creating them, and not cause havoc if I make a mess of one.

I had tried importing the wingsail weeks ago, which was the first (and separate) project, into the one I'm now using.  But F360 baulked, so I reverted to a saved copy of the current project and manually copied sketches into it etc. Looking for "best practices" as they'll save me frustration in the longer term.

For now, I'll probably start with a fresh component, and dump the one I'm making a mess of.  🙂

Cheers, Max

[TrippyLighting]

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@MaxHugen wrote:

...

 F360, maybe not the ideal tool for doing all the 3D curvy bits I have to deal with.

...

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In my experience 90% of that are users lack of understanding of how to work with spline and NURBS surfaces. 

If you work with "curvy things" and lofts in Fusion 360 you need to understand how NURBS surfaces work.

Here are links to some fundamentals from the Autodesk Alias documentation.

Autodesk Alias Theory Builders

Autodesk Alias Golden Rules

[MaxHugen]

Thanks for the links Peter. I'm used to the (fit point?) splines in Inkscape, where I can vary the length of each handle of a point. I am struggling a bit with the equal length handles, but I'll probably get used to it.

I also found the ability to change the point type in Inkscape so you could make a section between 2 points effectively a straight line useful, or change a point to create an edge, etc.

But you're quite right, there's still a lot I don't truly understand about spline curves and NURBS surfaces. Thanks for the links to the study material - there's so much returned by Google it can be difficult to find the right info sometimes. 🙂

[jeff_strater]

@MaxHugen - a  follow-up question:

"I'm used to the (fit point?) splines in Inkscape, where I can vary the length of each handle of a point. I am struggling a bit with the equal length handles" - can you explain more?  I am not familiar with Inkscape at all.  But, you can change the length of each tangent handle of a fit point spline independently in Fusion (unless you make them equal with a dimension or equal constraint, which I would not recommend).

One thing to be aware of in Fusion is that fit point splines are "global" in nature.  Change any fit point or tangent handle, and you can affect the entire curve.  Control Point Splines do not have this behavior - the changes are more localize to the spans near the point you are modifying.  This is part of why some people prefer to use that type of spline.

[MaxHugen]

This might explain some of the spline node (point) options in Inkscape. IMO it's a very accomplished program.

[TrippyLighting]

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@MaxHugen wrote:

Inkscape. IMO it's a very accomplished program.

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The purpose of splines in Fusion 360 is to create 3D geometry in the form of NURBS surfaces. That necessitates a specific mathematical form of spline.

The purpose of a spline in Inkscape is to only create an arbitrary 2D curve, which allows for more "options" in curve creation.

Math matters!

[jeff_strater]

ah, I see - a picture is worth 1000 words - unequal handles per side on a single point.  I had misinterpreted this as thinking that it meant you thought that all handles across the whole spline in Fusion had to be the same length.  Makes sense.  Yes, that would be nice.