Unable to loft a 3D sketch with rails and then use circular pattern on it

Unable to loft a 3D sketch with rails and then use circular pattern on it

angela.peralta
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Message 1 of 10

Unable to loft a 3D sketch with rails and then use circular pattern on it

angela.peralta
Explorer
Explorer

As the title says, I am having a frustrating time trying to create a loft with 2D sketches as rails. After giving up on the planned loft and making a normal loft, I am unable to create a circular pattern.

 

When I create the loft I use the base of the surface projected ellipse to the point where the lines intersect successfully. I am not able to add the rails of the 2D sketches afterwards. Sometimes it works for 1 of the 4 sides, but it doesn't do what I want it to do. 

 

I was able to loft close to the rails by changing the point condition to "Tangent" and changing the weight to 1.7. I would like to be able to get the exact shape I want but I'm just trying to get this prototype printed at this point. The problem after this loft is that I am unable to do a circular pattern with that loft.

 

Loft 1.pngLoft 2.png

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Message 2 of 10

peterKMFDM
Contributor
Contributor
Accepted solution

This is the "exact loft" - and it will pattern.

Message 3 of 10

SharkDesign
Mentor
Mentor

Do you need to loft, or can it be done with a revolve?

Does your last message mean you've solved this?

 

 

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Message 4 of 10

peterKMFDM
Contributor
Contributor

The last message includes the part with the correctly lofted 'lump' which can be patterned.  The loft can't be constructed as a revolved feature because it is elliptical in two planes.  I ran out of time to write more than a line of explanation 😁.

Message 5 of 10

JDMather
Consultant
Consultant

Sketch7 is not fully defined?

JDMather_0-1636398600161.png

Extrude43 does not look "right" to me?

 


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Message 6 of 10

angela.peralta
Explorer
Explorer

Works like a charm! Many thanks. I will have to learn more about how you did it.

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Message 7 of 10

angela.peralta
Explorer
Explorer

I would like to be able to loft it. For the real life function, revolve won't do it.

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Message 8 of 10

angela.peralta
Explorer
Explorer
Hmm interesting.. I guess I have to learn more about how to loft properly
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Message 9 of 10

peterKMFDM
Contributor
Contributor

Hmmm - @angela.peralta  - if you can define "properly" then we might be able to help.  In my book, if you model the shape we need to make, then it you've done it "properly".  Anything more becomes cad-snobbery, and usually takes too long 😉

 

There are probably easier methods, but I like this approach because you have complete control over "everything".  Lofting this shape isn't easy because the rails and sections all meet at three points - it's almost a revolve, but not quite.  This is how I tackled it:

Sketch the profilesSketch the profiles

Note the use of construction lines for the ellipse axis and 'normal' lines for the curves.  When you extrude the curves as a surface, you don't want the axis to be included.

Extrude each curve as a surface - AWAY from the finished shapeExtrude each curve as a surface - AWAY from the finished shape

By default, the sketches are consumed by the extrusions.  This is good because you don't want to accidentally select the sketches for the loft - you want to select the "Edge" of the extruded surface.  If the loft dialog box shows any "Curve" selections, go back and hide your sketches:

Select any two sections, and one rail.Select any two sections, and one rail.

The reason for using extruded surfaces as your inputs for the loft is so you can use them to control the tangency of the loft:

Set tangency condition for all edges.Set tangency condition for all edges.

 

That's it.  From here, make the input surfaces not visible, mirror the lofted surface, and use the "Sculpt" tool if you want the resulting shape filled with solid.

 

If you missed the tangency step, then the resulting surface will look wrong because the curvature drops away too quickly from the input surfaces.  If you turn on Zebra analysis, you can see the zebra lines do not "flow" over the surface.  The step in the zebra line is where it is missing tangency:

06.jpg

 

The cad-snob in me says it should look like this:

05.jpg

Hope it helps!

Message 10 of 10

SharkDesign
Mentor
Mentor

'CAD snobbery' = less errors 😉

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