Hi Olga, I see... - basically the problem here is that sweep will get confused if you use a scaling rail with a sharp corner in it.

Really it is intended that the scaling rail should be a completely smooth curve, that prevents the sweep from doing any sudden jumps in shape as it is stretched out to meet the scaling rail.

In these cases the scaling rail corner happens near the bottom of your ring, that is why there is some messy areas down in that spot.

I can see that the scaling rail gives you the kind of shape that you were wanting, but it is basically not going to work right for this particular kind of thing, it is just too difficult for the bottom tip of the sweep to be formed correctly using this method.

I'd really recommend sweep more for rings where you want a single totally smooth surface. If the body should have edges like you want for this style, then it is easiest to get a clean final result by not using sweep but instead do an extrusion and then boolean away the side parts to taper it, that's the kind of style that is shown in that post that Pilou linked to above.

Here is an overview of that using your curves:

I started by discarding a few pieces and drawing a line between the curved pieces like this:



Then you can select that profile with the curves and extrude it (use Both sides option):



Now select that extrusion and use Construct / Boolean / Diff and use the lines as the cutting objects:



That will cut the object into 3 pieces (shown slightly separated here for illustration), just delete the outer 2 pieces and the inside piece is the one you keep:



The surfaces created in this way will be much cleaner and should fillet without any difficulty - sweeping has the bad side effect of collapsing down to a single point at the tip, that type of collapsing tends to be hard to control right in that tip area.

Another way to do the boolean method is to have 2 fully closed profiles:



Then you can select them both, and run Construct / Boolean / Merge:



It will basically bundle all those previous steps up for you automatically.

- Michael

yes the fillet works but is it a normal fillet?

Hi Pilou, seems to have normal fillet results over here.

Here is the model using the boolean merge method:


Here is what I get with a fillet of radius 2:



It looks like in your case you may have filleted the original curves instead of the solid?

- Michael

< It looks like in your case you may have filleted the original curves instead of the solid?
no :) (same 3dm file than above) construction lines are erased!
Maybe it's the corner angle who makes problem? straight line / curve? Continuilty maybe impossible?
Not so bad but curious :)

Hi Pilou - that is actually working normally.

By selecting just the top loop you are telling MoI that you do not want to fillet the side pieces and that those should remain sharp.

To keep those edges sharp means that the fillets will have to be constructed in the way that you show - the only way to make them rounded in that area would be to also round that side edge as well.

The only other alternative would be to open up a gap in the model, like this:



The area shaded in red there would be a hole in the model.

It isn't possible to be simultaneously sharp and rounded and connected together all at the same time...

- Michael

Ok Perfect explanation ! And not obvious at first view :)

Despite of that result is not so bad, no hole, complete volume :)

Hi Michael

Thank you very much for your reply.
The answer is simple - the rail cannot be with angles.
This pretty much solves the problem
Thanks very much for additional tips.

HI Pilou
Thank you for the tutorial. This is really easy solution.

Regards
Olga