Shelling without bowtie geometry

[dangartland]

Hello,

I have had problems creating shells for many of my designs due to the shape of the models.

For example, this design has a curve at the bottom, I know that if I offset this surface too far this will create bowtie geometry, and will fail.

Surface offset limit before error

I have used three processes recommended to me from my posts and from others, which were:

Using the shell tool

Surface offset then stitching

Or surface thicken

I have tried these on multiple designs to create a shell but they all run into the same problem.

Is there any feature, add-ins, or other 3rd party programs that would create a shell and remove any bowtie overlaps, similar to the way an offset of this shape in a sketch would work, as shown below.

Sketch offset removes bowtie lines

Many thanks,

Dan

[ryan.bales]

This is probably best in Design Validate, Document so i've gone ahead and moved it.

Like others suggested, if i were going for exact i'd probably stitch the whole thing and use shell on the solid body. Then if i wanted to put it back to surfaces i'd simply unstitch the body and remove/edit whatever faces/surfaces i needed. On something like you have shown it takes a few moments to do this.

Otherwise Trim in the patch toolbar is made for cleaning these up.

There are likely some others with advice here too.

[dangartland]

Thank you for your response.

From your suggestion I have tried to use the trim feature to cut out overlapping surfaces, but in this case I can not even get the bottom curve to offset far enough. This was as far as I can get, the curve will cross itself before I can reach the required distance, meaning it can not be trimmed into place.

Trimmed surfaces

This is as far as I can get before the curve crosses over itself.

Curve limit

Is there another way to get this to work?

[TrippyLighting]

This is an area where you simply will hit limits in Fusion 360. My suspicion based on my own experience and conversations with users that have much more experience in surfacing than I do is that you are at the limits of what can be done with Fusion 360.

[ryan.bales]

Like i mentioned, offset and trim is not my preferred solution for this. And i agree with @TrippyLighting that you are really running into the limits of what Fusion can do.

[dangartland]

Thank you for both of your responses. It is unfortunate to hear that this just the limit on what Fusion can do.

Just so I can confirm, there are no other ways to create a shell other than:

• Surface offsetting and stitching
• Surface thickening
• Shelling tool

Is there an add-on which could help create shells?

Or as a work around is there a 3rd party program that could be used in conjunction with Fusion to shell a model and then bring it back into the design?

Is there any plan to improve the shelling functionality in the future Ryan? Or is this a permanent limit for Fusion?

Many thanks,

Dan

[TrippyLighting]

Could you share your model ? (export as .f3d and attach to post)

Shelling and offsetting surfaces are tasks of the geometric modeling kernel. That kernel is the same in Fusion 360 and Autodesk Inventor. However, Inventor is a more mature product and possibly offers more ability here.

[ryan.bales]

There is a lot of questions to unpack in this. I would not say its a permanent limit of what Fusion can or will be able to do. Fusion is always evolving and moving forward. 

I think your summary of how to create the offset shell is correct:

---

@dangartland wrote:

Just so I can confirm, there are no other ways to create a shell other than:

• Surface offsetting and stitching
• Surface thickening
• Shelling tool

---

These all do work, the finesse and cleanliness of them is different. I'm with @TrippyLighting, and sharing a model can help to show examples specific to your model and workflow. 

[dangartland]

Interesting to know that Inventor could be useful to move onto if we need it.

I am glad to hear that this is not necessarily a permanent limit to Fusion in the future.

I have attached the file to this reply, I hope this can help.

Many thanks,

Dan

[TrippyLighting]

I've looked at this model. You may remember me from helping you with other models on this forum. You've created a number of very artful forms that are not at all simple to create in any CAD, or modeling software.

There are two kinds of limitations you are dealing with. One are the limitations of the tools in Fusion 360 that help creating such objects. Some of that can be alleviated by applying proper modeling techniques. Modeling techniques  are the second limit you need to address.

Attempting to create this object as a single loft is quite a stretch (pun intended ;-). )

 Just looking at the sketches  it was clear to me that his was unlikely to create good geometry, a prerequisite for this to shell.

The curvature map tool speaks pretty clearly. 

It might be  much easier to design this with T-Splines than with surfacing tools unless you absolutely have to adhere to tight dimensional tolerances.