Hi Mala, for this case where you want the break line to be going in the sweep direction it would probably be good to put in profile curves in that area and reshape the center profile to have a fin rising above it like this:







- Michael

Michael, and thanks to Frenchy too, ...the last look pretty smart and it´s near to that what my goal is.
But...hmmm´...I cannot construct a sharp profil like you did which is additionally clean and well formed. When I trimm the curve in order to make the form like I want, it seems to be cutted.
Why is the connection lost for a smooth curve? Tried all trim commands, but still got the problem...
thx, Mala

Hi Mala, I'm sorry I'm not undertanding your question:

> When I trimm the curve in order to make the form like I want, it seems to be cutted.

The Trim command does cut a curve, that's the job that it is meant to do.

Is it that you want to add some points to the curve? If so use Edit > Add pt for that, not Trim.

Is there maybe a 2D vector program that you're familiar with that uses a type of Cut tool for adding points to a curve? If so then that's a little different than MoI, MoI's trim tool is for cutting a curve into pieces, not just for adding points for point editing.

- Michael

Hi Mala, sorry also another part that I don't understand, you wrote:

> Tried all trim commands, but still got the problem...

There is just one Trim command, what are the other ones?

- Michael

If you click on CTRL during the drawing you will have "Sharp" junctions between Control Points...

Till now you can't change a "Sharp" Control Point against a "Smooth" Point ! (or inverse)
So add one like you want and erase previous you don't want...and move the new one at the previous place! :)

Else another method you can use!

The Iso Curves! (Construct / Curves / Iso)
For easy selection and moving the Control Points!
Just Loft at the end!
Just taken 3 Top Iso for the concept here! :)

"... what are the other ones?"
I meant the different options for trimming...like keep together...etc.

"If you click on CTRL during the drawing you will have "Sharp" junctions between Control Points..."
Noticed no different in sharpness-.

I guess I got it...I used now the add points tool...merci, Michael and Frenchy...Cheers, best...Mala

PS: ctrl/strg for sharp is still interesting...

Hi Mala,

re:
> > "If you click on CTRL during the drawing you will have "Sharp" junctions between Control Points..."
> Noticed no different in sharpness-.

Here's an example - this is using the Draw curve > Freeform > Control Points command, and on the 3rd point I'm holding down the Ctrl key and you can see that it leaves a "corner point" that is sharp rather than making a smooth curve at that spot:



- Michael

Ok - michael, I see. I understood while holding the crtl-key and drawing a circle, the points are changed in order to solve my gone problem...sry, for my english...

On my ring I got a new challenge that I cant do.
I would like to have filleting but the fillet command does not work.
May you take a look why, please?
Best, Mala
P.S.:what I do not understand too is the size of the file...it is so extremely hy in comparison to the others I made until now?!

Hi Mala, how are you constructing this surface exactly? The file size has grown large because the surface is extremely dense with a huge number of control points in it.

For filleting, if you hide your curves you should be able to see that there is not any edge in the area you want to fillet, the surface is smooth there although it goes through a very tightly curved bend:





You'll probably need to build this in a some separate pieces instead of all in one single sweep.

- Michael

Something similar to this, making separate outer and inner pieces.

First an outside piece which will be cut by these planes:



And then discard these areas:



And then a smaller inner piece which will be cut by these planes:



And have these areas discarded:



So now the outside and inside remaining pieces look like this:



You can select these spots and do a Loft to connect them, then Edit > Join the pieces together:



Hope this helps!

- Michael

Michael - I got it. Thank you!!!
Mala

Hi, I noticed that there is a little construction problem - different differences at the lofting parts. See it atached.
I cutted the tubes with two different sized cubes. The littler one is 26 mm for the smaller ring. The bigger ring is trimmed with cube, 28 mm. Then I had to rotate the cubes horizontally for a special winkle I need. Then I cutted the two rings with the cubes. The result, in the file, are different distances at lofting-surfaces.

How would you place at beginning the cutting objects in order to avoid the distance differents at the lofts? Ideas?

kind regards, Mala

Hi Mala, sorry I'm not understanding the problem. It's just a normal fact of geometry and
mathematics that the projection of a rotated object does not keep equal distances in the projected view.

For example if you have a square in the Top view:



If you rotate it so that the plane of the square is not aligned with the top view:



Then the projection of it in the top view will not be a square with equal length sides anymore:



Your lofts have equal distances in 3D but they are at an angle to the top view so it is normal that the
projected lengths in the top view will not be equal.

- Michael

hmmm´...ok, Michael.
I tried an other way...but the result was exactly the same. I made a offset of the two big circles and moved it for 1 degree together. Sweep along the segment.
Perhaps someone has an idea somehow...best, Mala

As a cube can't have the same direction of 2 edges from the center of the circle
only when its 90° or 180° so you can't have that you want where you are!

Sections will always inclined so difference of distances between the 2 circles!
(in fact Ellipses & Circles)

Here little cube can't have 45° of the Angle center!


Here circles are drawn on the face section for show the deformation!
(they will be also ellipses by these triming lines!

The intersection of a cylinder and a plane is an ellipse.
The intersection of torus and plane is a toric section.
I think that your smaller ring is NOT a torus.???
So make the smaller ring by revolving a circle?

I need more study:-)

Brian

Or, per Michael, slant lengths are different, in different places, by the geometry.

Conversely, if equal slant lengths are the goal, the inner ring would have to be modified,
To be squished down to an undulating "ellipsoid" (or toric section?), cross section?

You have only circle sections of a tore when the triming curve/plane is perpendicular to the big perimeter! :)