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.

[TrippyLighting]

Please share the model. Export as .f3d an attach to post,

[karolisd]

Attached.

[TrippyLighting]

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@karolisd wrote:
Attached.

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Uhmm.. nope 😉

[karolisd]

I see them available for download under the post?

[TrippyLighting]

Oops! 😉

[TrippyLighting]

Lets take this back to the beginning and talk about curves. Those aren't necessarily the root cause of the current problem, but at some point in time they will be.

You use too many spline control point and it shows in the curvature comb. They are not terrible, but they can easily be improved by using fewer fit-point spline control points. and work with the tangent handles.

For such gentle curves I find it much easier to work with control point curves. I would start with a 3-degree curve with 4-control points and if that doesn't work use a 5-degree CV spline with 6 control points.

[karolisd]

The reason for adding those control points is that the board was actually measured at those points. This is also the reason for using the fixed point splines. As the curvature display shows, there are no sudden changes of direction on any of those points and the splines are smooth.

Also, not all of the points you see are spline control points. I had to add some regular points and make them coincident with the splines to mark the edges of the board rails.

Although there are 5 slice sketches in the project, only 3 of them are used for the loft. The other 2 are just for the reference so I know how far the shape is from the board I am trying to model.

[TrippyLighting]

Are you interested in learning appropriate techniques, or not?

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[karolisd]

Yes I am.

You are saying that those splines can be created with less control points and I'm not arguing with that. I just explained why those points were created in the first place. If you prefer I can remove some control points and reupload.

[TrippyLighting]

Is the bottom of this surf board supposed to be flat?

I see, for example that the tail has a spline on the bottom.

If this needs to be truly flat, ten that should be a "regular" line with a horizontal constraint applied.

[karolisd]

The tail could be flat or almost flat, but the rest of the board has a very clear concave.

[karolisd]

Here is the board with less control points. The nose actually looks better, but in general the issue is not solved, I still get the ugly corners and I don't know how to control the loft in the front. I might want to create a completely round nose for example.

[karolisd]

Regarding that horizontal constraint you mentioned, it is applied to the handle, not the spline. The bottom is slightly curved, although not much.

[TrippyLighting]

Attached is one way to create this using surface lofts. I would not approach this with solid lofts.

I left out one of the loft profiles toward the front to achieve better surface flow.

[karolisd]

@TrippyLighting thank you for providing this example. I will have to study it a little bit more, as I have very little experience with surface modelling. Could you explain why surface lofts have an advantage over solid loft here?

I also noticed that the end result doesn't address my main concern - the nose of the board is sharp and thin, the same as in my "Loft to Point" solid example. 

[davebYYPCU]

Can’t get to a desktop for a while.  Do the board in sections.  Front one having left right and centre profiles.

We do wing tips, by dividing the last full profile at the centre line.  Create / make on the centre line at the nose a profile that reaches back to the two half profiles.

Use these 3 profiles, and rail in the outline to include all 3 profiles, or you get Loft error messages.

(ThIs is hard to put into words). 

Might help...

[TrippyLighting]

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@karolisd wrote:

 Could you explain why surface lofts have an advantage over solid loft here?

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Much better control! 

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@karolisd wrote:

I also noticed that the end result doesn't address my main concern 

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My main objective was to show you the technique.

The key her is how I created the rail that coincides and defines the lower edge of the board.

Your rail was somewhere on the outer perimeter of the loft, which is why the tip looked suboptimal

The same technique can be applied to your other design.

I still, however would structure the workflow differently. Again, the main topic for me is to have the most control over the outcome and a stable design. 

[TrippyLighting · Accepted solution]

Again, If I would do this from scratch I'd follow a slightly different strategy.:

The tip needs a better approach, but  a little sandpaper should be able to take care of it as well 😉

[karolisd]

Thanks for the update. It will take some time to digest the surface modelling approach. The "more control" part comes at a cost of "much more complicated design", but if that's what it takes to create a proper shape, I'm OK with it.

I do have an issue with the new side rail though. It's a 3d spline and from my previous experience, it is so difficult (for me) to edit those splines that I generally consider them non editable. To go around this issue, I projected the spline control points to both XZ and YZ planes, created 2x2D splines and then used their intersection curve as a side rail. This adds more complexity, but at least I can (relatively) easy edit the shape of the rail. Do you have any better suggestions how to handle this issue?