Loft problems

[jtbarker4]

Loft will work no problem from section 1 to section2 but will not solve for section 3 or 4. I have spent many hours on a solution with no luck. Any help would be appreciated. I would call myself a beginner.

Thanks

[JamesLodge01]

Hi There.

I downloaded you file, thankyou for sharing.

After preliminary inspection, it seems that you have a lot of unwanted geometry overlapping/intersecting geometry in Sections 1, 2 and 4. I have been able to generate a successful loft between 1, 2 and 3 but there also seems to be an issue with Section 4 when connecting to Section 3. 

When I originally tested the loft feature the warning a[[eared stating that there was an issue with input geometry. This prompted me to check the sketch geometry. you will notice point appearing in positions around the closed loop. These pointed are associated with unwanted geometry that overlap the required geometry creating each loop. An example of this can be seen in the attached image Intersecting Geometry.

I have also attached the file I worked on showing the loft between Sections 1, 2 and 3. This was successful after deleting unwanted intersection geometry from the Section Sketches.

Advice: Have a closer look at each sketch and ensure that the profiles are joined correctly with no unwanted geometry intersecting the profile or overlapping the profiles. Attempting to Fully Constrain your sketch geometry will also help you generate more robust sketch profiles making it easier to spot issues that sometimes occur when sketching in the future. Hope this helps 🙂

[temple_dawson]

I think the issue may be related to what each profile is comprised of. I opened your file, and the first thing I noticed was that the profiles are not curves, but many small straight line segments. It reminds me of what happens when you vectorize an image into a DXF.

I would suggest: opening each sketch profile, locking the unconstrained sketch profile, then use a fit point spline to best trace the shape, then redraw your rails (it may help to place one or two points on each of the profiles), and perform the loft. Make sure to hide or delete the line segments so that it is the smooth profiles you are using for the loft.

Edit: I saw JamesLodge01's reply after posting, and agree with his statement regarding unwanted geometry.

[TrippyLighting]

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@jtbarker4 wrote:

 I would call myself a beginner.

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One of the worst things a beginner can do is import geometry without understanding what exactly it contains and then try to work on it with more advanced features, such as loft.

These profiles are not curves but are constructed from a high number of straight line segments, which, when lofted (or extrude etc.) will create a high number of surface segments. That is not desirable.

Also, for loft to work well across all section, all those crosssections should have the same number of line segments, so Fusion has a chance to work out the mapping. That can sometimes be helped by connecting the proper mapping points with a loft rail.

My recommendation would be to use these sketches only as a visual guideline and try to replicate the profiles with Fusions native spline tools. Even then, the splines in each section should have the same number of fit points or control points.

[JamesLodge01]

I can also agree with @TrippyLighting with regards to how the rail segments are created. You will find that some of the rail segments are not constrained correctly and as per my previous post also have intersecting / overlapping line geometry. A general tidy up of the geometry is needed to get the loft feature working correctly. I'm sure it is possible but you will need to review each section sketch and clean all unwanted geometry and generate better interconnecting rails. 

[jtbarker4]

Thanks for your responses. I retraced section 3 as described  but still no luck. I ran the downloaded file with section 2 and 3 connected. I deleted the lofts and tried to recreate the loft but even on your modified file I get the error "Warning: The operation failed.
Try adjusting the values or changing the input geometry." Could you elaborate on how to look for unwanted geometry?

Just zoom in and look or are there methods? All the shapes extrude normally.

I am unsure on how to constrain a point spline shape.

The original was an imported DFX.

Thanks for the help.

[etfrench · Accepted solution]

I would redraw each section using control point splines.  They are a lot easier to get fair curves than fit point splines.

Note: I started with a small circle, which is why the curvature comb shows the abrupt endings