Hi all

I tried the procedure of extrude and shell/offset with simple geo w/o any problem. But with my model of this seashell it just wont work givin the faces a little thickness.
Hopefully u guys have some help for me?

Thanx,
Rogurt

Hi Rogurt,

The problem is the two last surfaces as shown in this picture.



If you zoom up on one of these surfaces you'll see the ends have a tight bend in them as shown below,
if the radius of the bend is tighter than the shell thickness then it won't work, if you apply a thickness of 0.2 it will thicken,
but if you zoom in on that area you'll see it starting to look funky, I did notice that you can apply a thickness of 1 with the
'Direction' option to 'Flip' but again you get some funky surfaces happening. If you try thickening excluding those two surfaces it works fine,
so if you tidy up the two end surfaces to have less of a tight bend it should work out.



Cheers

Thanks a lot. When the splines are lofted to the nurbs and I click "done" there´s no way tweaking the object anymore, is there? So how would you procede eleminating these problem areas?

Edit: aha. seems like I just mustn´t delete the original splines to keep it editable...

Now I cleaned up these areas. Unfortunately still offset/shell wont work (tried 0,2 + flip)...

Hi Rogurt,

I did modify the outermost curves with history enabled.
Here's my try:

Hi Rogurt,

> Now I cleaned up these areas. Unfortunately still offset/shell
> wont work (tried 0,2 + flip)...

Are you using MoI v1 or the MoI v2 beta?

I loaded your newest file shell_04-2.3dm that you attached into the latest v2 beta, and I am able to generate an offset of 0.2 units.

But there are still some problem areas with those side pieces.

The offset looks like this:



This seems to be due to a messy area right near the corner of one that surface, if you look closely you can see some irregular shading here:



That likely means that the surface is not well formed in that area, it actually has a tiny spot where the surface is actually folded back on top of itself, so the surface normal actually changes a lot in that little area.

It looks like that surface may have been created such that they are tangent to one another at the corner rather than forming a distinct corner? It can be better to avoid creating surfaces that are configured that way and instead build a larger surface and trim it.

With something complex like this, you may just want to model the inner or outer surface more directly by lofting/sweeping/whatever it as well instead of trying to offset it.

Offset is especially sensitive to areas where there are self-intersections, folding or overlapping, or tight bends in the surfaces. You need to have more simplified and regularity in the shapes for it to really have a chance.

- Michael

Hi Rogurt, see here for an example of how to make a rounded edge without making a degenerate corner:
http://moi3d.com/forum/index.php?webtag=MOI&msg=3473.3

- Michael

Hi Rogurt, also see this other post here:

http://moi3d.com/forum/index.php?webtag=MOI&msg=1127.4

For a description and illustration of what a degenerate corner on a surface looks like.

When a surface has its own control point grid organized in this way it is easy for the surface to become self intersecting as shown there, and that basically creates a micro tiny fold in the surface and that means the surface normal (which is a key thing used in offsets) can flip around wildly in that little spot.

So rather than making a surface that has that kind of degenerate corner in it, it will be better for offset to have a larger surface that has its control points in a more regular grid pattern instead of having corners of the grid bunched or stretched, and then have a trim curve that cuts away the excess area of the surface.

You can have all kinds of complex trim curves on a surface without it affecting the surface normal, but if the surface's own control points are bunched up or folded back on themselves it is a no-go for offsetting that.

- Michael

Thank you all.
@Paolo I understand these 3 samples are edits displaying the development from left to right. I tried to offset/shell the left one by 0,2 - wont work.
@Michael I am using the V1 30 days trial. I haven´t got a key so no v2 beta download.

All right. Now I dumped the whole shell attempt and duplicated the object, scaled it and did a boole. Result looks fine and calculation is way faster than "shell". So on to the next question: how can I bevel the upper edges via "filet" since I havent got continuus edges/splines I could select...

Thanx for your patience with me so far :-)

> So on to the next question: how can I bevel the upper
> edges via "filet" since I havent got continuus edges/splines
> I could select...

Hi Rogurt, I'm not exactly sure wehat you mean by not having "continuous edges" - surely you must have a set of edges that touch each other?

You can select multiple edges to be filleted, you don't only have to select a single edge at a time.

So for example here I've selected 3 different edges at the top of this object:



And then I ran Fillet to make this result:




Edges that are not smooth to one another will have "corner patches" added to them to connect them up.


One thing to be aware of though is that Fillet is also a sensitive command similar in several ways to Offset. In fact a part of the fillet calculation involves generating offset surfaces and intersecting them.

So if you have things like little folded areas or tight bends in your shapes, it is likely to cause a problem with fillet in a similar way it caused problems with offsets.

- Michael

I would also note that in a couple of his questions he is typing "0,2" as a value for his inputs (note the comma)

Is this a typo in the question or is this the value he is trying to fillet??? (It was the same value in the shell question....)

Hi Burr, in some other countries (for example France), the decimal digit separator is the comma character and not the period character like you are used to.

So for example in some countries they write the number "two and a half" in decimal form like this: 2,5


When your regional settings in Windows are set to use the comma character as the decimal separator, then you can enter in values like that into MoI.


See here for more details than you would want to know ;)
http://en.wikipedia.org/wiki/Decimal_separator


- Michael

OIC. Thanks for clarification.