Need help with a surfboard loft

[karolisd]

Hi Fusion community,

I need some help with my surfboard design. I sketched some cross sections of a surfboard and then lofted those sections to create a solid body. I used a single point as the last loft section (nose) of the board. Here is the screenshot:

In Fusion it looked almost perfect, but when I cut this board with a CNC, i noticed the nose is very thin and sharp and has a slight corner on the deck. 

I want the nose thicker and more rounded. To address this issue, I thought I would create a small profile and use it as the last loft section instead of a single point. After that I should be able to use fillet to round it if needed. Sounds easy, right? Well......

Now my board has some strange corners on the bottom. It seems that the shape of those corners depends on the shape of the nose sketch, but no matter how I draw the nose, I can't get rid of the bottom corners. 

OK, so next thing I tried to do is go back to "loft to point" approach, but round the profile line around the point. Unfortunately, no go. Fusion complains about non-smooth neighbourhood of a point:

I would appreciate any ideas how to thicken the nose of the board.

[davebYYPCU]

You are correct, Tangent Constraint to a Spline is not available, unless using the spline end point.  Can be fudged, but not totally accurate.

A fillet in one section sketch, Lofted to a next section sketch that has no fillet is similar to a modelled variable fillet, no?

I was intending to suggest Tsplines for your new question, but they are not parametric.

Having watched your section sketches evolve, I think you should develop the base shape, (workflow) and add the rear end crease separately.

I was able to review an early file you supplied and found the nose and sketch 1320 incapable of being utilised as supplied for my suggested workflow.  I saw that the thread was updated to solved and moved on.

Might help.....

[TrippyLighting]

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@karolisd wrote:

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@TrippyLighting wrote:

I'll look at this in more detail later.

In the meantime read my last post in this thread.

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I did, but I wasn't sure I understood it well.

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Then you should by all means download the model and go through my description step-by-step.

If there is something you are not sure about, you should ask.

Before proceeding with your design we need to make sure that you have sketching down. that is particularly true if you want to later make parametric changes. that requires rock-slid sketching techniques.

As it pertains to your fillet, the default fillet is a rolling-ball fillet. Do you understand what that means?

Look at the edge you want to apply the fillet to.

At the tail end, the 2 surfaces meet as an angle. Moving to the front  angel; becomes shallower and shallower until at the very front profile the two surfaces are tangent. What is the fillet tool supposed to do ?

[karolisd]

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@TrippyLighting wrote:

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Then you should by all means download the model and go through my description step-by-step.

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I downloaded it  and went through the description. In fact the model that I uploaded last is almost identical to your example, with the exception that I use intersection curve for the rail.

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@TrippyLighting wrote:

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If there is something you are not sure about, you should ask.

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@TrippyLighting wrote:

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I would use a surface based alternative to the workflow you describe with 2D sketches

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That is a little bit abstract. There are 10+ sketches in the model. The only place where I thought a surface based approach could be used was the rail intersection curve. I asked about that a few posts ago.

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@TrippyLighting wrote:

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What is the fillet tool supposed to do ?

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Probably generate a surface by rolling a ball along the edge. While it is difficult to say what it should do internally, I know what it shouldn't do. It shouldn't freeze my computer or cause Fusion 360 to crash. I had Fusion crash 5-7 times yesterday. This is one hard way to learn to save after each change.

[TrippyLighting]

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@karolisd wrote:

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In fact the model that I uploaded last is almost identical to your example, with the exception that I use intersection curve for the rail.

• Your design starts with creating construction planes for loft profiles. Mine does not.
• Your design then proceeds to create sketches with  loft profiles. My design starts with loft rails.
• The loft profiles contain mirrored fit-point splines. My profile sketches use 3-degree and 5-degree single span control point splines, that are not mirrored.
• You use too many loft profiles resulting an a fairly uneven loft.
• I don't use an intersection curve but an extruded, trimmed surface. I've explained why. Again I use a control point spline with the least number of control points to accurately represent the shape.
•  My loft profile sketches are coincident constrained to points that were intersect-projected from the loft rails.   

I don't see too many similarities!

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@karolisd wrote:

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The only place where I thought a surface based approach could be used was the rail intersection curve. I asked about that a few posts ago.

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That is what I meant and that is also the workflow that I show in the  model you supposedly downloaded and understood.

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@karolisd wrote:

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@TrippyLighting wrote:

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What is the fillet tool supposed to do ?

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Probably generate a surface by rolling a ball along the edge. 

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Correct. How would that surface look like?

@karolisd wrote:

I know what it shouldn't do. It shouldn't freeze my computer or cause Fusion 360 to crash. 

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I agree that Fusion 360 should not crash, but I did not ask you what it should not do. I asked what It should do and you can still not answer that question.

[TrippyLighting]

Attached is another approach including a chord fillet. But that might also be changed to a constant radius fillet.

This only to demonstrate technique. You might practice with your desired geometry.

[karolisd]

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@TrippyLighting wrote:

• Your design starts with creating construction planes for loft profiles. Mine does not.
• Your design then proceeds to create sketches with  loft profiles. My design starts with loft rails.
• The loft profiles contain mirrored fit-point splines. My profile sketches use 3-degree and 5-degree single span control point splines, that are not mirrored.
• You use too many loft profiles resulting an a fairly uneven loft.
• I don't use an intersection curve but an extruded, trimmed surface. I've explained why. Again I use a control point spline with the least number of control points to accurately represent the shape.
•  My loft profile sketches are coincident constrained to points that were intersect-projected from the loft rails.   

I don't see too many similarities!

Are you sure you didn't forget to upload the design? The last upload I found was "Loft to Profile trippy.f3d" on ‎09-22-2022 05:38 PM. Most of the things you describe here are not present in that file or I don't know how to look.

[TrippyLighting]

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Are you sure you didn't forget to upload the design? 

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I did indeed forget to upload the design, but is attached to the post now.

The "trick" for the fillet is to create an edge where the two surfaces meet at a clear angle and do NOT slowly become tangent.

That is one of the reasons Fusion 360 sometimes "thinks" so long. It really tries to find  solution. Sometimes it does, sometimes it doesn't. Even if it does, when it takes long a time, its a sign that it has encountered problems and the feature may break when design inputs are changed.

For a one-off that might be OK, but for a parametric design that undergoes changes, it is better to find a more robust solution

[karolisd]

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@TrippyLighting wrote:

Attached is another approach including a chord fillet. But that might also be changed to a constant radius fillet.

This only to demonstrate technique. You might practice with your desired geometry.

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This new upload does contain the things you mentioned earlier (starting with the rail instead of cross sections etc) and yes the approach is very much different. But.... the result is a bottom that is completely flat with no concave at all. To add that concave I would probably still need to draw the cross section first.

[karolisd]

I think the answer to the concave problem would be to add the bottom curves to the sketches, loft through them and then use the new loft for the bottom instead of the extruded surface. Will play around. Thanks.

[TrippyLighting]

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@karolisd wrote:

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To add that concave I would probably still need to draw the cross section first.

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Nope!

[karolisd]

@TrippyLighting, can you explain what those pink lines are in Sketch6? They seem to match the ones from Sketch1?

[TrippyLighting]

They are projected edges from the lofts, so I can create a tangent constraint for the spline at the upper edge. On the  lower edge I don't apply a tangent constraint to make sure I have a clear angle between the two adjacent surfaces so I can create a fillet .

I've attached an updated model with concave bottom to play with.

[laughingcreek]

@TrippyLighting -

I'm getting off topic here.  looking at your file, loft 4 - profile 3 is in sketch 9, but sketch 9 is after loft 4 in the timeline?  scratching my head why this works-

[karolisd]

What can I say, this is a very nice layout! Especially for designing a new board from scratch. 

Is there any documentation about how "Tangent" and "Connected" edges behave in Fusion 360? Is Tangent something like a curvature constraint for lines?

I will try to migrate my current model into this workflow and see if I manage to get a board that is similar enough. ATM I don't see why it shouldn't be possible. One thing I am still wondering about is how to make this edge completely smooth:

The model scale is probably around 1:10 compared to the real world board size. So the 0.25mm fillet would correspond to 2.5mm fillet when scaled 1:1.  I tried to increase the fillet radius at the center, but it doesn't want to go above 0.3. If I had a choice, I would use something like 10mm fillet for the board (1mm in the scale of the current sketch). The requirement is completely sharp at the tail and completely smooth from the middle of the board and up. The area from the fins to the center of the board being the transition area. So I either need to make the center section profile smooth or find a way to apply a bigger fillet radius.

Other than that, this setup seems to be close to perfect 🙂

[karolisd]

If I suppress the sketch, the loft also gets suppressed:

Apparently Loft4 has a crystal ball and knows the future 🙂

[TrippyLighting]

@laughingcreek 

To say in Steve Job's words "It works like magic and boy have we patented it" LOL

But, honestly, I did not notice that!

While I did move some stuff around in the timeline, a loft earlier in the timeline should not be able to use a sketch later in the timeline.

@jeff_strater can you look at this, please?

[karolisd]

So I started another redesign of the same board from scratch... for the 8th time 😄

I followed the example of @TrippyLighting , had some questions but in general everything connected fine. I had the board lofted and stitched into a solid body etc. Then I started to adjust the model to fit the shape that I need, and ..... lofts started throwing errors on every change that i make! 

Here is one: Rails can not be tangent to profiles!

Tangent? i created the profiles using intersection points...

This happened when I adjusted the tail concave  shape by some 1mm, so my guess the problem should be on the tail side. If I change the same concave randomly to one side or the other, it starts working again. Sometimes I have a feeling Fusion was designed to drive people crazy.

[TrippyLighting]

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@karolisd wrote:

Sometimes I have a feeling Fusion was designed to drive people crazy.

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That isn't intentional, but I does sometimes have that effect. Lofting can be very finicky in Fusion 360!

[karolisd]

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@TrippyLighting wrote:

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@karolisd wrote:

Sometimes I have a feeling Fusion was designed to drive people crazy.

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That isn't intentional, but I does sometimes have that effect. Lofting can be very finicky in Fusion 360!

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I know!  I went to the gym to let the steam out other wise I don't think my monitor would now be standing in one piece now! I need to relax, get a coffee and try to persuade myself that I'm enjoying this. 

[TrippyLighting]

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@karolisd wrote:

The requirement is completely sharp at the tail and completely smooth from the middle of the board and up. The area from the fins to the center of the board being the transition area.

Can you make a top or side view screenshot and simply put a pointer where you want this to be sharp and where you would the fillet to start ?

I guess in the real world a truly sharp edge does not exist, so a .5mm fillet (or even .25mm) at the tail would work?