Hi People

As shown on the Picture, i am trying to connect those 2 edges.



As i do, the new developed surface looks broken and unsmooth.




I just dont get it. Can anybody tell me how to connect those 2 edges with a smooth surface?
Is there a mistake in the construction logic?

i ve attached 2 files, one trimmed surface like in the screenshot and one untrimmed surface.


thank you

Hi ksiksu,

> Is there a mistake in the construction logic?

Sort of, yes - the problem is you've got such a long single segment curve that has those tight little corner areas in it.

It's difficult for a surface to be created between 2 such curves with nice alignment between those corner areas.

Because these are just long splines the surfacing command doesn't really know that you would like just the corner areas in particular to exactly correspond with each other, it will just kind of make connections between the surfaces using things like equal distance traveled along each of them, which makes for connections like this (here I've drawn in connection lines in red):





So that's what is producing that kind of slight twisting effect - connections happening between the curves at different locations than having each corner connected to the other corner only.

The way to solve this is to make your original curves made out of some different segments with one segment for the long straight piece and other segments for the corners. Then with 2 curves made out of an equal number of segments between them a surfacing command (like Loft for example which is probably what you'd want to use here) will know to make connections from each segment to the other segment, that will make the corners match up well.

I'll see if I can give an example.

- Michael

Hi ksiksu, so instead of all one big long curve that has some little tight corner areas inside of the single segment, you want to instead have separate segments for those corner areas.

Probably the easiest way to do that is to make your initial curve have totally sharp corner areas , either by using several different drawing commands to create it (and snapping on to the endpoints of previous segments for each new drawn piece) and then using Edit > Join to join them together, or you can also do it all within the Freeform curve command by holding down the Ctrl key (or checking the "Make corner point" option) for points that you want to make sharp.

Sharp corners will set up the base segments for the curve, since there will be one segment in between each sharp area.

Check out the attachment sharp_corners1.3dm for what this looks like.


Then you can use the Fillet command to round off those corners, each rounded fillet piece will be a separate segment.

But in your original shape some corners were very tightly bent in a small area - you may want to just have such areas be totally sharp instead of trying to put in such a tiny tightly bent area in at all.

Then to put in rounded corners with the Fillet command you would select that sharp-cornered curve, then run Construct > Fillet, then right-click to tell it you want to do all vertices and enter in your fillet radius.

That will produce a result like I've attached in the file filleted_corners1.3dm

So notice that if you select this curve and use Edit > Separate on it, it breaks apart into individual pieces for each long straight piece and each corner piece - this is the kind of segmentation that you want.

Now you would repeat that for the outer curve, or if you want to have 2 curves that are separated by a constant distance from one another you can use the Construct > Offset command to create the outer curve at a constant thickness away from this one, which is what I did.

Then I trimmed the surface with these segmented curves, to get the result in new_trimmed.3dm - note that you don't need to project curves on to the surface as a separate step before the trim, there is projection built in to Trim itself so you can just trim the surface with these 2d curves directly.

The resulting cut areas are made out of 1 edge for each segment in the original curves, and now you can select pairs of them like this:



And then use the Construct > Loft command to build a surface between those edges like this:



Go through and repeat that for every matching pair of edges, and because things are broken down into each corner as a separate matching segment you will get proper matching this way.


So the kind of key thing is that if you want to get some particular matching between some specific small region of a curve like a tight bent area, that area should be broken out into separate segments in the original curves instead of it just being some kind of interior zone of a single long curve segment.

Hope this helps!

- Michael