Hi all,
I've included a drawing of a tube with sharp angled cut planes. There is a plane which corresponds with the cut on one end. I would like to extend the tube beyond that plane but I can't figure out a way to extend it and make the tube longer.
Can anyone help me?

Thanks,
Mark

Hi Mark - you would probably normally just use the original profile that you created the tube from and extrude that profile curve to make a new longer section.

Do you not have the original generator curve saved anywhere?

If not then you can recover it by doing an "untrim" on those surfaces - see here for some more information on untrim:
http://moi3d.com/forum/index.php?webtag=MOI&msg=444.4

Basically if you select those 2 tube surfaces and turn on their surface control points with Edit > Show pts, you'll see that their underlying surfaces are already actually extended how you want - you can recover those by doing an untrim.

When you do a boolean or trim on surfaces, there are new "trim curves" that are created on each surface which mark areas of the surface as being holes or cut away regions, but the original surface is still there underneath all those trim curves and when you do an untrim as shown in that link above you can recover that full surface.

I've attached a version of your file here with those tube surfaces untrimmed and with the original full extended tube recovered. I created this version by selecting one edge of each of those surfaces, and then doing a Ctrl+A so that all the edges on each one were selected, and then pushing Delete to remove those trimming boundaries.

Hope this helps!

- Michael

Hi Michael,
I tried to duplicate what you did, but when I select the two tube surfaces and then show points I get a set of points that describe rectangles. If I delete those points, then the tubes just go away. What am I doing wrong?

I wanted to extend the tubes above that flat surface but NOT below the more complex ends on the other end of the tubes (if that makes any sense). I can't find the original generators for the tubes, and, in any event, generating the surface on the bottom end of the tubes was quite difficult. I did it sometime ago and I'm not sure I can remember how to do it again. Is there a way to extend the tubes in just one direction, ie above and away from that flat surface?

What I'm going to do is open the drawing in Rhino and then use its unwrap command to produce a flat representation of the tubes. (See attachment to see what I mean.) I've done it before but I need to extend that tube in the one direction so I can add some other details to the flat representation. (I hope this is making sense.) Does this help you to understand what I'm trying to do?

Thanks again,
Mark

I have not follow but a simple Extrude by Dir for the internal cylinder don't make the trick ?



For the external cylinder
You trim the existing cylinder by a straight line for obtain a section then extrude it again by Dir



And if you want keep your old complex ending form, copy it where you want and trim the new cylinder with it!

Hi Mark,

> I tried to duplicate what you did, but when I select the two tube
> surfaces and then show points I get a set of points that describe rectangles.

Yup, this "show points" part is just for seeing the size of the underlying surface.



> If I delete those points, then the tubes just go away. What am I doing wrong?

You don't want to delete the points, it's the trimming boundaries (edges) that you want to delete - here's the steps that I wrote above again, pay particular attention to the part in bold:

"I've attached a version of your file here with those tube surfaces untrimmed and with the original full extended tube recovered. I created this version by selecting one edge of each of those surfaces, and then doing a Ctrl+A so that all the edges on each one were selected, and then pushing Delete to remove those trimming boundaries."

So the steps are to make an edge selection, not a control point selection - turning on control points is just the way to visualize the size of the underlying surface that's underneath all the trimming information.


> I wanted to extend the tubes above that flat surface but NOT below the more
> complex ends on the other end of the tubes (if that makes any sense).

After untrimming it gets extended in both directions, and then if you want the other end to stay as it was before you can then use Edit > Trim on the new big surfaces and cut them with the pieces on the other end. Sometimes in preparation for the retrim it can be convenient to do a ctrl+c copy of the edges before you hit delete to remove them, then after they are deleted and the surfaces are untrimmed do a ctrl+v to paste them back in and then those are used as cutting objects for the Trim.

That's what I did to produce the result in the attached version - it now has the bottom trimmed off to how it was before and the top is extended, is this what you needed?

Also if you like you can just keep your old pieces exactly how they were and construct your extended piece as a separate object by duplicating the end edges of the 2 surfaces in the double-end extended piece (to duplicate edges select them and then do Ctrl+C and then Ctrl+V) and then you will have some profile curves that you can extrude however you need to build the extended part and then cut the original with the extended piece. The untrimmed + retrimmed version is kind of cleaner though since it's all one single big surface rather than made up of multiple pieces.

- Michael

Hi Pilou,

> I have not follow but a simple Extrude by Dir for the internal cylinder
> don't make the trick ?

That works too, but it will create a surface that has a kind of slanted structure to it. That's not too bad but it's kind of nice for a cylinder to be represented by the extrusion of a circle that is perpendicular to the cylinder's axis just to have the most simple kind of end result that would match up with an analytic cylinder primitive.

- Michael

I had just reloaded the unrolled_patern.3dm file, so don't know that was a filled tube! :)

And the external section was composed of some arcs sections for some reasons (?)

And don't know in what direction must be the extrusion :)

At this subject :)

here I had made a Blend or a straight Loft then Boolean Union the 3 parts (it's surfaces) why the 2 sections don't disapear?
What is the rule ? If I have 3 same rectangular faces, Boolean Union them make only one face and edges common disapear!
It's because cylinder has been trimed not in perpendicular section? (same with a normal cylinder :)

Hi Pilou, boolean union does some special work when unioning co-planar planes together that will reform them into one single big plane.

It can also do some special work for the case of unioning together 2 pieces that have the same full underlying surface to combine those together into a single surface as well.

The situation you have there does not fit into either of those special cases, so there won't be any special handling for it to make it any different from the regular generic handling, and in general booleans work by potentially cutting up surfaces into smaller pieces but for gluing things together the generic way is for the pieces to become joined.


> It's because cylinder has been trimed not in perpendicular section?

No, it's because there is special extra work done in the plane/plane case.

- Michael

Thx for the explanation :this is always a little not evident result to accept :)

Hi Pilou, also consider that in order to remove the edges between pieces it is necessary to form just one single surface out of the different surfaces that you currently have.

That's difficult to do automatically in cases where the different surfaces have different control point structures in them or meet only at internal trim edges instead of only meeting at edges of the underlying surfaces.

Planes are a special case where it's easier for the code to know that 2 planes that touch each other and have the same plane normal can be represented ok by just one single larger plane. For other kinds of surfaces it is more difficult to construct code that would be able to analyze the surfaces to determine that.

- Michael

2 same primitive cylinder Bolean union have only the internal common faces dispears but not the common section :)
But I understand that must be an headache to resolve all cases!

Hi Pilou,

> 2 same primitive cylinder Bolean union have only the internal common
> faces dispears but not the common section :)

Yup, that's normal - notice that I did not list cylinder surface combining as one of the special cases that are currently handled ?

It could be possible for that particular case to happen in the future, it would require some modifications to some pretty complex areas of the geometry library though.

In the meantime usually it is possible to solve such things yourself if you want to eliminate internal edges by creating one larger cylinder and trimming it to the proper boundaries.

Also if your 2 cylinders were made up of pieces cut out from one single large cylinder, they will combine in that case since it then is handled by the "same underlying surface" special case. So for example if you draw a tall cylinder, and then cut it in half with a horizontal line to make 2 cylinders that way, if you then boolean union those pieces together it will reform into one single cylinder piece. This can be handy sometimes, because it can sometimes be convenient to carve off a chunk of a model using boolean difference, then do some work on the individual pieces and then when you union it back you will then get surface combining - that's done in the "Crown of clubs" tutorial video for example which is why the final unioned piece does not have extra edges at the bottom of each club where they connect to the bottom part that was carved off from the whole initial revolve.

- Michael

< then cut it in half with a horizontal line to make 2 cylinders that way, if you then boolean union those pieces together it will reform into one single cylinder piece.
It's that who is very pertubating! :)
2 copy cylinders don't union + disapear, 2 cylinders from a cutting one yes! :)

Hi Pilou,

> 2 copy cylinders don't union + disapear, 2 cylinders from a cutting one yes! :)

Yes - it's because there is special case handling used for the situation of "2 surfaces that are each trimmed surfaces using the exact same underlying surface" - that case is more straightforward for the code to detect that the surfaces can be combined together.

For that case and for planes there are mechanisms in place in the booleans to try and reform the unioned result with larger glued together surfaces. For other kinds of cases like the 2 copied cylinders - that is a different case and would require different handling in order for it to work, which is certainly possible but not implemented currently in the geometry kernel.

- Michael

Michael,
Thanks for the help. I think I've got it now.
Mark