Invalid result body using shell tool

Ok… I’ve got an ellipse that is 37.5mm x 76.2mm (radius). I extruded that with a draft angle of 6 degrees and a length of 165.1mm. Now, when I use the Shell tool to hollow out the walls I get the above error when I specify a thickness of 2mm. If I change the thickness to 1.1mm I do not get the error. Anything thicker than 1.1 fails with the error. Is that due to the shape of the ellipse or ?? For now I’ll stick with 1.1 and move on with my prototyping. Just wanted to ask. Thanks!


As Ellipses are altered from the basic Length to Height ratio of 2:1 [say, 100mm to 50mm] to a narrower Cigar shape, with parallel sides, it reduces the possible Shell thickness.
Factor in the introduction of sloping sides and the possibilities become severely restricted.

In the the above Post you have probably obtained the thickest possible Shell for that overall ‘shape’.
Circular and Square shapes behave much better. Lofted shapes can also be problematic.

S3D is great because usually there is a route to achieving the result required.
In this case a workaround

Hopefully you will be working from a Duplicate of your original Design?

Use the above Extruded Body, prior to applying the Shell feature.

Select this Body and hit the ✚ Icon and Move it vertically clear of the Original Body.

Deselect the Copy Body and select the Original Body
Use Transform > Scale move the Slider downward a little and type in 80 [in this case]
Note that this will also have the effect of raising the base, of the Original Body, off the Plane

Deselect the Original and Select the Copy Body, use the Arrow to lower it into position
Align the two base Faces
Use Tools > Subtract to remove the Original from the Copy Body

If you want to experiment to achieve a different ‘shell’ thickness simply hit Undo until the situation prior to the point where the Scale feature was used:

This presents a somewhat uneven ‘shell’ thickness that could be improved by adjusting the size and or shape of the Subtraction Body rather than simply Scaling?

I think that you’re probably right on here… The flatter that ellipse gets, the less able the sides are to be uniform in thickness… I tried printing the resulting object with 1.1mm thickness which was the max it would allow and the first two prints failed. I decided I needed to re-do the object with a slightly different shape to get the 2mm wall thickness I’m after. Thanks so much!!

During sleep my mind often gets ‘raked over’, like gathering leaves into a pile to reveal what may be lying on the ground.

This is an altered Base Profile used in used in my ScreenShot above, with Sketch > Offset > Loop applied and of course you can set the Offset measurement as required, The Height of the Inner Body is 300mm and the Outer Body 305mm, in this case:

The beauty of this is the accuracy of the result.
However as can bee seen the ratio is close to basic, and height increase becomes a significant factor to consider. The Draft Angle refuses to be set beyond, as yet, undefined limits.
So Experiment is the Key to success.

Credit is due to @GiddsV in:

For introducing this possibility to me.

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Thanks @Gelphyn! You’re inspiring me to try tools I’ve not yet tried! I was able to get my funky shape going… A little adjustments allowed me to define the wall thickness at 2mm (or was it 2.5?) last night without issue. I just finished it up and will attempt a print for this prototyping that I’m attempting. Thanks so much!!

Good luck with the Printing @ps23Rick

When it comes to trying different Tools it is good practice to ensure that every aspect is investigated.
Far from being boring it can be quite exciting discovering new Features. It can be quite time consuming so it would be advantageous to maximise the process. This can be achieved as described below, rest assured the benefits will outweigh the effort needed.

My MO is to work through ALL available features in ALL Menus to find out what each is capable of.
I did this first toward the end of June 2019, however S3D does not stand still for long so there is a need to revisit often. There are 'clues, within S3D Version History in the App Store, as to changes that have been made. But the detail is sadly lacking so ‘suck it and see’ seems to be the best option.