Another fiilet question

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 From:  WarrenM
6008.1 
I've been trying to avoid stepping on landmines with MOI so I can get fillets to behave consistently but I feel like a blind man sometimes. This SEEMS like it should work. I built this shape up pretty slowly and checked these edges out as I went and all was OK ... until it wasn't. Basically, I can't get these edges to fillet:



Can someone look at this and tell me why the inner curves will fillet but the outer ones won't? I'm trying to get a handle on the rules.

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 From:  Frenchy Pilou (PILOU)
6008.2 In reply to 6008.1 
Take the vertical line with the 2 parts of the curve and that will work! ;)
You have a sharp angle between the 2 curves so its' difficult for the Fillet engine!
It's not a cool continuity!
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 From:  WarrenM
6008.3 In reply to 6008.2 
You mean take out that vertical line? How?
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 From:  Michael Gibson
6008.4 In reply to 6008.1 
Hi Warren, do you mean you're trying to fillet just that one single edge all by itself instead of the whole sequence of them?

It's more surprising to me that the inner one actually works - it generally should not work to fillet just one single edge of a sequence like that because you're asking the filleter to kind of open up a hole in your model and it doesn't know how to fill in that hole. Check out here for a related example:
http://moi3d.com/forum/index.php?webtag=MOI&msg=5091.4

In some situations it can fill things in by extending the surrounding surfaces, but that's a complex operation and it's difficult for that to work very well when the surrounding surfaces are meeting at a shallow angle like you've got here.

It's much better for the filleter to have surfaces that either meet each other smoothly or come to a more distinct sharper crease where they meet. Here the different arc segments that you have making up the boundary are not smooth with one another, they form a crease where they touch but it's at a shallow 15 degree angle, so somewhat close to being smooth but not actually smooth. These kinds of situations where things kind of approach being smooth with one another make things more difficult for the filleter because when it tries to extend pieces and then intersect the extensions, the extensions kind have a region of overlap with one another rather than making a crisp intersection.

Normally for a shape like you've got here you would want the pieces to be smooth to one another and then when you were filleting it you would want to select the whole ring of edges around the entire object to fillet rather than just one single edge.

- Michael
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 From:  WarrenM
6008.5 In reply to 6008.4 
Well, I WAS trying to do the whole ring but it wouldn't work which is why I was trying to identify the problem by selecting smaller and smaller sets of edges. I burrowed down to find that outside curve was the issue which is why I posted it. I want to do the whole ring, don't get me wrong. :)

I guess the problem lies in how I created the outer scallop shape in the first place then? That vertical line seems to be the fun killer. Is there a way to remove it or does it all come down to how I create things in the first place? Basically, get the first steps right or it's never going to work?

Is the general idea in MoI "large sweeping actions" rather than "small, cumulative actions"?
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 From:  mjs (MSHIDELER)
6008.6 In reply to 6008.1 
I think part of the problem is that your outer radius / circular scallop feature is not tangent with the inner radius / scallop feature.

I created, in your file, a similar profile and with a single click, put a fillet of 2 units on the whole thing just by clicking one edge. Since I made my initial sketch with tangent relationships the fillet was able to 'chain' around all the edges in one shot.

If you look at your object from the top view and zoom in close to where the outer and inner radii meet you can see that the outer rounded surface runs out just past the point of tangency while the inner radii comes up short of being tangent. What you will need to do is either make the outer radii the driver and adjust the inner radius to meet tangent, adjust the inner radii as the drive and make the outer radius match tangent or split the difference.

The image attached shows you in black lines, how your profile sketches cannot be tangent....ever. While the red line for the inner radii shows how you can use the outer radius as the driver while changing the inner radius in order to run tangent as it should be.

This isn't a MoI or other program issue but just modeling practice. I have had my knees skinned a few times too but best to learn as soon as possible.
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 From:  WarrenM
6008.7 In reply to 6008.6 
Very helpful, thank you!

I tend to create my extrusion shapes by boolean'ing together a series of 2D shapes first so I guess I need to pay more careful attention to how those shapes connect up with each other. Definitely a learning curve here and I appreciate the help! NURBs modeling isn't something I do every day...
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 From:  WarrenM
6008.8 In reply to 6008.7 
Nice, so through building with a different mindset I was able to get it to fillet. Looks awesome in 3DSMax too.

OK, so I just need to come to grips with NURBs modeling then. Gotta make room for yet another workflow in my tiny brain. :)

Thanks all!


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 From:  mjs (MSHIDELER)
6008.9 In reply to 6008.8 
Nice work.
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 From:  Frenchy Pilou (PILOU)
6008.10 In reply to 6008.7 
Yes the vertical one can permit to fill all the Curves in the same time! Of course with a very little fillet!
But of course that makes a fillet also on the vertical one! :)
But as said previous your curves were not well reccorded! :)

EDITED: 4 Jul 2013 by PILOU

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 From:  Michael Gibson
6008.11 In reply to 6008.5 
Hi Warren, it sounds like you've got this figured out now, but just in case:

> I guess the problem lies in how I created the outer scallop shape in the first place then?
> That vertical line seems to be the fun killer. Is there a way to remove it or does it all come
> down to how I create things in the first place?

The vertical line is a problem because the surfaces on either side of it are not smooth to one another, they come to about a 15 degree angle and these kinds of shallow angles where things are sort of close to being smooth but not quite actually smooth tends to make things difficult for filleting.

It isn't necessary to totally remove those vertical lines, but what you want is for the surfaces on either side of it to be tangent to one another rather than only slightly creased to one another.


> Basically, get the first steps right or it's never going to work?

Yeah it helps avoid a lot of problems if your original curves that were extruded were tangent to one another.

For filleting it's usually best if things meet at a sharp angle to one another or are smooth where they meet. Things that are just kind of close to being smooth but not actually smooth (like say 5 or 10 or even 15 degrees off like in your case here) make things a lot more difficult for the filleting mechanism. That's because anytime you have pieces meeting sharply to one another at all the fillet segments that follow them will not line up directly to one another and will need to be trimmed or have corner juncture pieces put in place, and when things at at shallow angle the various calculations that go into that become more difficult.

- Michael
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 From:  Michael Gibson
6008.12 In reply to 6008.5 
Hi Warren,

> Is the general idea in MoI "large sweeping actions" rather than "small, cumulative actions"?

It kind of depends on the particular circumstance. But it can make things easier for filleting if you have larger pieces because a single large non-segmented curve or large surface piece will be all smooth inside of it. So that can tend to avoid ending up with things meeting up at some slight shallow angle.

Slight shallow angles between pieces will tend to cause problems with filleting.

- Michael
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 From:  ed (EDDYF)
6008.13 
" ... I tend to create my extrusion shapes by boolean'ing together a series of 2D shapes first"

I've had good luck building smooth 2D profile closed curves by drawing the critical segments first, then use Blends to bridge the gaps. That is, use Blend to create the radius transitions to complete the closed curve.

This has given me no problems when it comes time to extrude and fillet the resulting solid.

Perhaps Michael can chime in and explain if a Blend on two line segments will always be tangent where they join.

I may be drawing curves in a more complex way than necessary, but I find Blend works well for 2D drawings.

Click image to enlarge.

Ed

EDITED: 4 Jul 2013 by EDDYF

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 From:  mjs (MSHIDELER)
6008.14 In reply to 6008.13 
A great way of creating tangent relationships.
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 From:  Michael Gibson
6008.15 In reply to 6008.13 
HI ed,

> Perhaps Michael can chime in and explain if a Blend on two line segments
> will always be tangent where they join.

Yup, a blend between 2 line segments will be tangent to each line segment.

- Michael
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 From:  Frenchy Pilou (PILOU)
6008.16 
Does this the same in the 3D Space when curves are and come from anywhere orientation ?
I suppose yes but ...

EDITED: 4 Jul 2013 by PILOU

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 From:  Michael Gibson
6008.17 In reply to 6008.16 
Hi Pilou,

> Does this the same in the 3D Space when curves are and come from anywhere orientation ?

Yes, the blend will still be tangent to each curve even if the curves are not in the same plane.

The blend part itself will not be flat in cases like that, it will bank around to meet up with the curves.

- Michael
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 From:  Frenchy Pilou (PILOU)
6008.18 In reply to 6008.17 
Thx now I am sure! :)
---
Pilou
Is beautiful that please without concept!
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 From:  WarrenM
6008.19 In reply to 6008.14 
Nice! That's really helpful, thanks for the Blend tip.
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