topic Re: 3D sketches constraint issue... again (sorry about that!) in Fusion Design, Validate & Document Forum

3D sketches constraint issue... again (sorry about that!)

nicolas.leduc.mail — Mon, 03 Jan 2022 18:54:36 GMT

Hi,

I'm fairly new to Fusion 360. I used to work wth Catia for CAD something like 15 years ago... Let's assume I'm a complete newbie !

I currently use Fusion for hull design of model ships. I try to perform lofting of the hull surface, from the sheer line and keel line profiles and according to station lines as rails.

1. I use a 3D sketch to draw the sheer line with splines from blueprints set as canevases. Then, I draw a keel line in the XY plane. Those two sketches intersect at two points in the XY plane.

2.Each station line is drawn as a 2D sketch in a XZ plane.

3. I use Projet> Include > Intersect to draw the intersection of each station line plane with the sheer line. Doing so, profile and rails snap to each other. So far, so good.

However, every time I want to tweak the sheer line a little, those intersections unsnap (no coincident constraint?) and I have to start the whole process again.

Is there a way to preserve the link between station line sketch and sheer line/keel line sketches?

Attached is my complete file (Please let me know if I need to reduce it?)

Any kind of help would be greatly appreciated !

Re: 3D sketches constraint issue... again (sorry about that!)

TrippyLighting — Mon, 03 Jan 2022 19:07:19 GMT

You'll need to share the model. Export it as a .f3d file and attach it to the next post.

Re: 3D sketches constraint issue... again (sorry about that!)

nicolas.leduc.mail — Mon, 03 Jan 2022 22:01:00 GMT

Of course !

Sorry about that. I thought I had uploaded the file, but well, I spend my holidays in a country with very limited bandwidth and connectivity...

I removed the canevases to reduce the size of the file.

Re: 3D sketches constraint issue... again (sorry about that!)

jeff_strater — Mon, 03 Jan 2022 22:03:20 GMT

I did a quick test, just to see whether it does work as I expect it. While I don't understand what all these terms mean, I at least know what a ship looks like. So, I created a sketch for the keel, and a few sketches for sections along the length of the keel sketch. I used Project -> Intersect to project the intersection of the keel spline into each sketch, then snapped another spline to that point. I found that I could go back and edit the keel spline, and the intersections seem to update correctly. So, the basics work. Will need more info to go beyond that.

One question, though: When you say "I want to tweak the sheer line a little", I'm curious about that "tweak". If, by chance, you do any delete/recreate of that line, then I would expect the intersections to come apart, as they are tracking the actual curves selected. If it's not that, then it could be some other workflow difference.

Re: 3D sketches constraint issue... again (sorry about that!)

nicolas.leduc.mail — Mon, 03 Jan 2022 22:30:49 GMT

To be fair, I take the following page as an example.

https://modelshipworld.com/topic/19657-an-attempt-at-hull-modeling-with-fusion-360-loft-rails/

We are currently trying to modestly improve our proficiency in CAD to enhance our skills as modelists...

I believe CNC & 3D printing would be of great value for our club.

Best regards,

Nicolas

Re: 3D sketches constraint issue... again (sorry about that!)

jeff_strater — Mon, 03 Jan 2022 22:37:04 GMT

Oh, I see the problem. This is a Direct Modeling design. Sketch Projections (regular or intersections) never update in a Direct Modeling design. Use a Parametric (History-based) design, and things should work.

Re: 3D sketches constraint issue... again (sorry about that!)

nicolas.leduc.mail — Tue, 04 Jan 2022 01:05:12 GMT

This is very interesting.

I wondered about wether this could be related. And this solution is actually very sound: it seems logical that constraints should follow a timeline to update in the propoer way.

Thank you for this answer.

Time for me to start from scratch, I guess !

Re: 3D sketches constraint issue... again (sorry about that!)

TrippyLighting — Tue, 04 Jan 2022 01:09:23 GMT

@nicolas.leduc.mail wrote:

Time for me to start from scratch, I guess !

Yep, and while you're at it, use the least amount of spline control, points, and the least amount of profiles and rails you can get away with. I followed the link you provided and the approach with all these profiles will not result in a smooth loft.

Re: 3D sketches constraint issue... again (sorry about that!)

nicolas.leduc.mail — Fri, 07 Jan 2022 19:30:27 GMT

Hi again,

With the timeline on, I started the ship design from scratch.

Every rail is connected properly with all profiles. I tried to keep the nodes for 2D/3D splines to a minimum.

Yet, error messages keep appearing when trying to loft:

- Error: There must be at least one intermediate non-point profile for a loft.

- Error: A point profile can only be used as the first or last profile of a loft.

- Warning: The selected rail does not touch all of the profiles. (which is really odd this time).

This is driving me nuts ! However I noticed that on the method discussed on the previous link, the designer seems to loft on 'open profiles', that is without enclosing the profiles as real surfaces.

Could that be the issue here?

I also tried to connect profiles with coincident dots, without success so far.

Any help would be greatly appreciated !

I prepared a screencast (which has been uploaded o my profile) but I noticed no possibility to link it to this reply. Is that normal?

A simplified F3D file with just 3 profiles and a few rails summarizes the issue.

I will try to take some time to explore this idea about 'closed surfaces' or open profiles, since I seem to lack some basic understanding about those lofts.

Best regards,

Nicolas

Re: 3D sketches constraint issue... again (sorry about that!)

TrippyLighting — Fri, 07 Jan 2022 20:53:21 GMT

Creating a boat hull with such drastic changes in curvature in a single loft is not something I'd advise. In any CAD software.

Your splines still have too many spline control points. You might be able to construct a loft but the surface quality will not be great.

All 6 sketch features in the timeline of your design are highlighted in yellow, indicating warnings.

Also, while one should never say never, I would never create a fit point spline with more than 2 points as a 3D spline. The curvature of such a spline is impossible to control.

If you want to loft from the top to the bottom (or vice versa) you need a rail on the XZ plane for the front and rear to control the loft.

You would first create the top and bottom profile.

Then the front and Rear Rails.

You would then create a couple of construction planes, and sketches for loft rails on those planes. You'd use the sketch->project->intersect function to project the points into those sketches where the loft profiles intersect those planes. You need to use those points to create the loft rails.

Re: 3D sketches constraint issue... again (sorry about that!)

laughingcreek — Fri, 07 Jan 2022 20:44:30 GMT

can you post a model with your canvases?

Re: 3D sketches constraint issue... again (sorry about that!)

jeff_strater — Fri, 07 Jan 2022 22:02:33 GMT

These errors are all relatively easy to explain:

The first two, I believe are probably caused by inadvertently selecting a Point when selecting a profile/section.

- Error: There must be at least one intermediate non-point profile for a loft.

- Error: A point profile can only be used as the first or last profile of a loft.

It is easy to do, especially in surface loft. You are trying to click on a curve, and unintentionally click on one of the fit points. Then you see a loft that goes down to a point:

If you select two of them as your profiles, you get the first error:

Similarly, if you inadvertently pick one for a middle section, you get the second error:

- Warning: The selected rail does not touch all of the profiles. (which is really odd this time).

I did not get this error with your design. I did, however, get a self-intersecting surface result:

that one is probably because of the curvature in the rails, but I don't know for certain

Re: 3D sketches constraint issue... again (sorry about that!)

nicolas.leduc.mail — Sat, 08 Jan 2022 10:08:56 GMT

Thank your for your answer.

I understand your point. But now this is getting silly: How do you select the profile without actually clicking on one of the fit points? The curve itself is not clickable when the loft panel is open?

Re: 3D sketches constraint issue... again (sorry about that!)

nicolas.leduc.mail — Sat, 08 Jan 2022 10:19:42 GMT

Thank you for the quick answer !
About your remarks on the overall strategy: I perfectly understant your point. I am well aware that surface won't be that accurate. Yet, the point is to get an overall shape for the model ship. All parts are made with wood, so we are quite accustomed to refine the shapes and to taper all of them. What other way would you use to model the hull from canvases?

To answer about loft control: I can draw 2 more rails in the XZ plane in the front and rear. Actually in my first attempt, I had longer profiles connecting with each other on the XZ plane. I can replace this with a rail.
The rest of your instructions is what I did with the current solution.

Re: 3D sketches constraint issue... again (sorry about that!)

TrippyLighting — Sat, 08 Jan 2022 11:40:47 GMT

Please share some images of the ship or boat in question. As I understand it, you already had some images inserted as canvases in your first model but removed them to save space. once we have the images we can provide better feedback and perhaps a screencast.

Until you have succeeded in creating a loft using your curves, you won't be able to fully understand what I posted. It requires some experience with the behavior of NURBS surfaces.

Re: 3D sketches constraint issue... again (sorry about that!)

nicolas.leduc.mail — Sat, 08 Jan 2022 17:02:30 GMT

Here you go.

Beware, everything is in French onnn this complete file...

Re: 3D sketches constraint issue... again (sorry about that!)

TrippyLighting — Sat, 08 Jan 2022 17:06:33 GMT

There is no file attached to your post.

Re: 3D sketches constraint issue... again (sorry about that!)

nicolas.leduc.mail — Sat, 08 Jan 2022 17:47:44 GMT

Here you go. Sorry, still bandwidth issues.

The canvases are included. they come from a relatively old monography about said ship.

I just translated everything in english. I think It should be understandable.

I also added a forward rail in the XZ plane as well as a rear rail (but 3D).

I agree that I won't comprehend fully until I have at least one loft actually functionnal... Yet, the guys posting on this nautical research guild forum seemed quite satisfied with their own results. Obtaining those may have been very time consuming though.

I'm really sorry to bother you with this.

Re: 3D sketches constraint issue... again (sorry about that!)

nicolas.leduc.mail — Sun, 09 Jan 2022 14:21:30 GMT

Hi,
Finally found out what the problem was.
As expected, it was very silly: I was actually trying to loft from the BODY/LOFT function instead of the SURFACE/LOFT function.... hence the issues...
I finally got a lofted half-hull.
It is indeed a bit wavy at the moment, some rails are not perfect and there are still some warnings. I will keep you posted about what I get, including the accuracy of length and area measurements.
I will post a few pictures as soon as I can.
And I would be really interested in what other kind of design path I should have chosen instead.

Thank you all for your help.

Best regards,
Nicolas

Re: 3D sketches constraint issue... again (sorry about that!)

nicolas.leduc.mail — Sun, 09 Jan 2022 20:10:07 GMT

Allright,

First attempts are a limited success.

Indeed, the curvature of the hull is complex.

As such, sometimes lofting fails when selecting some of the consecutive rails (self-intersecting loft). This situation can be resolved selecting a rail further located along the hull, then selecting again the previous rail.

However, the rear is too complex. I can't get satisfying results yet. I will try :

- Lofting parts of the hull then assembling

- Using more rails.

Of note, profiles and rails can inverted. results seem quite similar for the moment.