Hi andras, a couple of different things happening for your #1

First thing - for blending it is a good idea to blend between 2 open edges.

But your blend target does not have an open edge, it is a solid. I'm talking about this piece here:




There are 2 faces that are connected to an edge in a solid like that, and it will be kind of random which face will be picked to be the blend target in a case like that.

To make it not random, it is a good idea to select the top face of your solid there and delete it, that will help to clarify that the vertical face is the blend target, because that will then be the only face that is attached to that edge.

Some more info in a minute...

- Michael

Hi andras, some more information on your #1.

So when you do a blend between 2 closed edges like this for example:



Part of the controls that will come up is a "seam alignment point" that will let you adjust how the 2 closed curves are being connected together, it will show up as 2 small points like this:




If you do a the blend on your #1 case, you will notice that you do not have those points available. That's because the top edge there has a little tiny gap in it:






That's a big enough gap that the blending code does not consider that top edge to be closed.

The blending mechanism will only be able to put up an adjustable "seam point" for blending between 2 closed edges, when edges are not closed they can only be flipped to help with orientation, not "re-seamed".

How was the top edge curve created for your #1 case, was it from trimming your previous shape that you posted followed by Merge or was it from some other steps?

Whatever produced that top edge may need to be tuned up to "true up" the endpoints when there is a topologically closed loop being formed but the endpoints are slightly apart from one another.

- Michael

Hi andras, also another problem that you will kind of run into is that trying to make a blend that covers a rather large distance and between shapes that have a tighter bend in them will tend to make bunching.

That's because blending tries to keep its surface to be perpendicular to the edges.

When something is forced to be perpendicular, and also travel a fair distance, and also go through a tight enough curve all at the same time, it tends to create a kind of "bunching" like this:



That will probably create some surface artifacts like weird little wiggles in your result when there is not quite enough space for the blend to easily fit.

- Michael

yes I know this effect I have already met with this several times I keep in my mind.
The MERGE command finally worked well thank you. Just I dont understand is this an separate command? because firstly I tried between the Boolean Merge and finally with the Shortcut method... that was fine.

Hi andras,

> The MERGE command finally worked well thank you. Just I dont
> understand is this an separate command?

Well, even though it has a similar name it does a different kind of thing than the BooleanMerge command.

BooleanMerge will intersect surfaces with one another and extract all volumes that are produced.

The other Merge command is about merging 2 edges that touch one another into a single edge.

They do different things so they are different commands.

- Michael