Hi Rudy -

> 1- First I did not understand Pilou's way to make that shape into a solid (See JPG)

Pilou used the "rail revolve" tool. To do that, run Construct / Revolve / Rail revolve, and then when prompted, pick the profile curve and rail curve that Pilou shows, and after that you will be prompted to pick a revolution axis line, similar to regular revolve. Pick the 2 axis points on the endpoints that Pilou shows the dotted line between, and you will get that result.


> 2- I am trying to shell the new, all curved, brick shape and cannot do it. See file
> (shell from bottom). Am I doing again something wrong?

Shelling is really pretty sensitive to small inaccuracies or irregularities in models. Similar to fillet, it can get confused pretty easily in situations where there are several small edges or corners coming together.

In this case the shell will succeed with small values (like up to 0.05 or so), but it gets confused with pieces running into each other with larger values.

Your model has these kinds of corners:



That's basically not a very clean and simple structure where the different parts are meeting up, things are kind of broken up into different little edge pieces there, that's what is problematic.

It looks like this is the result of small differences differences between your different arc curves that make up the shapes - like you've got one that is about a 53.4 degree arc and a different one is like a 53.5 degree arc. They also not quite in line with each other, the bottom of one does not quite line up exactly with the bottom of the other set: (shown here zoomed in a bit)




Everything is fairly close to being lined up, but isn't quite close enough. Small inaccuracies and little mis-alignments tend to get magnified as you do more operations to the results of the curves, and that eventually ends up creating more complex corners and little tiny edges on the final results instead of simple structures.

So to create something that can be shelled successfully, you've got to be quite rigorous about the accuracy of your original curves, things need to be aligned more precisely to get a cleaner result.

One big tip for this is if you want to create symmetrical pieces, draw one and then duplicate it using tools like Transform/Mirror or Transform/Rotate, rather than trying to sketch a close equivalent. Creating an exact duplicate will help to ensure alignment. And it is actually quicker to duplicate than to re-draw.

I've attached a reconstructed version of your model as curved_brick_3.3dm (in the .zip file), this version should now shell properly.

The way I reconstructed it is I threw away everything except for one of your arc curves. I did a Transform/Rotate with checking the "Make copies" checkbox to make one copy at 90 degrees rotation, and then did Transform/Mirror on each of the arcs to create an exact mirror image duplicate. Then I drew lines to connect them and went through the extrude + boolean intersection procedure.

This result has a nice simple edge structure because all the pieces lined up exactly, so the intersections between the different objects were very clean and predictable, and symmetrical. So the final resulting edges come right together at a single shared point instead of being slightly off.

For some purposes you don't need to worry so much about such detailed accuracy, some things can tolerate it more than others. But shelling and filleting tend to be the least tolerant.

I hope this helps!

- Michael