Difficulty with "Bad Geometry" while lofting.

[fliesblindthroughcrapstorms]

I attempting to create semicircular tracks for a marble machine type of kinetic sculpture. Most often to do this I will create multiple profiles and loft them.  Sweeping would be simpler but often introduces undesireable twisting. More and more frequently the loft fails with "bad geometry". Sometimes redrawing the geometry works, more often it doesn't. I have included a file with a copy of some particularly troublesom geometry. I have a version of the sketch before I expanded (rotate twice and offset) the profile(s) and one after. I see no reason this shouldn't warp and buckle the way it does. Can anyone recommend a method to solce and hopefully avoid this?

[wersy · Accepted solution]

I would use sweep.

[fliesblindthroughcrapstorms]

$&+π§€$#

My phone slipped and I hit "Accept as Solution". I can't use sweep, it introduces unacceptable rotation.

[TrippyLighting]

Please share your model by exporting it in .f3d format and attaching it to the next post.

That does NOT work by replying per email from a phone. You'll have to use the Forums web interface.

Have you tried to use a sweep with guide rail?

Scratch that. I should pay better attention 😉

If you break this down into 4 individual surface lofts and two patches on the end, it will work.

[davebYYPCU]

Hollow Pipe, 

Loft a cutter plane, for split body, to cut the top off.

From Trippys pic, seems like a lot of blue sketching, and no Rail/s.  
Not checked the file.

@TrippyLighting - one Loft, Thicken and 2 fillets doesn’t do it?

Might help….

[TrippyLighting]

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@davebYYPCU wrote:

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@TrippyLighting - one Loft, Thicken and 2 fillets doesn’t do it?

Nope, you need to check the file 😉

[davebYYPCU]

Works for me, would need different profile, but .....

Might help....

[TrippyLighting]

@davebYYPCU I'd love to see what magic trick you used to create EXACTLY the geometry outlined by the series of profiles in the OP's design.

Can you share the model so we can learn from it?

It would have already helped if you had shown tangent edges and the sketches 😉

[davebYYPCU]

Original file,

Lofted the outside curves,

thickened inside 2.5 and

4 fillet edges at 1.15.  Don't think Full Round would work didn't try it.

I mentioned that a different profile would be required, for exact match.

Might help....

[TrippyLighting]

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@davebYYPCU wrote:

...

Lofted the outside curves,

thickened inside 2.5 and

4 fillet edges at 1.15.  Don't think Full Round would work didn't try it.

I mentioned that a different profile would be required, for exact match.

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Of course that works. It just doesn't accomplish the EXACT task 😉 

I did try a full round fillet and doubtful it would work. It did not work.

I do agree with @wersy that a sweep (with  guide rail) would likely work best, but again , it would need different inputs. 

[fliesblindthroughcrapstorms]

I tried the hollow tube/cutting plane approach first - but when the track curves back on/near itself, such as with loops, this creates other problems and complications. I am looking for a loft solution beause it also allows me to control the rotation step-by-step and also allows me to make the ball carrying profile more or less than 180 degrees.

[TrippyLighting · Accepted solution]

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@fliesblindthroughcrapstorms wrote:

... I am looking for a loft solution beause it also allows me to control the rotation step-by-step and also allows me to make the ball carrying profile more or less than 180 degrees.

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A loft solution does not guarantee a consistent cross-section along the entire lofted geometry.
In fact, the more profiles you have the higher the chance is that the geometry will be inconsistent between those profiles.

A sweep with guide rail can accomplish the rotation of a swept profile along a path to arbitrary degrees, as long as the geometry does not self intersect.

[fliesblindthroughcrapstorms]

Would you believe I had never done a sweep with a guide rail before? This is going to change a lot, thank you.