Despite all the forum threads I keep as pdfs in my MoI tutes file I still don't seem to have got my mind into gear about the doos and donts of filleting.

Has anyone done a collection of "Filleting Rules"?

(As you get older the "black holes" of what the mind wont register grows larger!)

Brian

Hi Brian, could you please post the .3dm file of your object as well? That would help to see what might be going wrong in your particular case.

It looks like you may have some pretty tight bends in there, one thing to look out for is that it does not work well to ask for a fillet radius that is larger than the radius of the tightest curve in the edge to be filleted.

There is some description and illustration of that one in the fillet documentation:
http://moi3d.com/1.0/docs/moi_command_reference7.htm#fillet

- Michael

Thanks Michael.
I have been through that Help Manual and --maybe--something is not sinking in?--or, I am expecting something outside the limits?

Sorry to worry you

Brian

Brian,
Not that I am a pro, but the front edge of your main airfoil seems to intersect the fuselage at a very tight angle, I suspect the filet radius on that kind of geometry would be the issue. Dont forget that filets are a way to save time for designers, but at the end of the day, if you are actually planning on using this model to make an aircraft, you probably want to fully control the interface between those two b-reps so that you can better control the aerodynamics of that structure. If your just doing this for fun, try opening up that front interface angle and reducing your filet radius.

Hope this helps,

Adam.

Adam

Thanks for the response but "nomenclature" problems---

"----interface between those two b-reps" ???

"--try opening up that "front interface angle"???

Is my age showing?

Brian

PS----YES, I am doing it for FUN!
I think I deserve a design medal when compared to the Spitfires I used to draw in my school books in the early 1940s!

Hi Brian, thanks for posting the model, that really helps to see what is going on.

One thing that is really going to mess up the filleting in this situation is the back edge of the wing which already tries to come in kind of smooth to the main body, it is at a very very shallow angle, kind of practically pre-filleted already:





When you want to set up something for filleting, it will actually tend to mess it up a lot if your surfaces are partly blending together as if they were filleted already, that's kind of what you've got in the above situation.

Instead, the spot that you want to fillet should have the surfaces meeting at more of a sharp crease, kind of a more distinct edge rather than partially smooth already.

More like this for example:



Then fillet will work a lot better on the more distinct edge:




Basically if the edge to be filleted has surfaces that are already partially smooth together, that creates a difficult situation for it.

So don't try to make it so smooth initially, you can make it approach it somewhat but not to the degree at the spot where I showed above. Instead let that area be more of a sharp edge and let the fillet smooth it out instead of trying to build it partially smooth already.

Hope this helps!

- Michael

Thanks as usual Michael.

The thing is that I didnt "---- try to make it so smooth initially"

The design concept well---sort of have happened "visually." When (I) get those concepts it's very hard
to visualise in depth the problems that may occur later (?obviously with a lot of my work).

Is something similar a problem with the tail? I got the vertical part to fillet!

Brian

PS---
Doing a sweep approach is just so simple ---but!

Hi Brian, the tail is something different.

It is definitely meeting at a good angle, not at all similar to that other problem.

It looks like what happened there is that you didn't quite push the tail through the body quite far enough for it to punch all the way through, here is a view down into the inside of that section:



Notice that area looks like it did not fully punch through the outside surface:



I think that one would probably fillet fine if those parts got pushed a little bit more in when they were booleaned so they fully punched through the outer skin instead of only partially, although there is not very much room left there until it runs into the fillet on the vertical part.

- Michael

Hi Brian, actually there is one other issue with that tail as well, which is that it isn't very good to try and fillet a very thin "knife edge" type situation like that.

You can see that the vertical section did fillet, but it did not produce a very good result in the back:





It is tough for the filleter to produce a nice corner in such a sharply angled "knife edge" situation like that.

If you want to fillet that well, it would probably be necessary to first fillet that very sharp edge so that it was a slightly rounded edge first (probably actually best to put a small rounded piece in there early on from the initial sweep actually), and then boolean the pieces together, then do a fillet where they met and it would then not have that "knife edge corner patch" type issue.

Filleting things that come to a very sharp angle generally can cause problems for MoI's filleter. You may have some better luck with those particular knife-edged ones in ViaCAD instead of MoI.

- Michael

Ahhhhh!

Thanks Michael.

Brian

Hello

As you're talking about it, will Viacad (pro) be a better alternative than rhino to extend my actuall MoI toolset ?
For the moment I switch time to time to rhino for :

- the surface continuity option with the sweep or network tool
- the patch tool
- sometimes to use the sweep tool when Moi's distribution failed to give a nice result.

Of course Rhino do the right job for this, but it's a bit expensive for the 3 tools I use.

As I'm still a noob in this cad world, I don't really get the difference between viacad and Moi/Rhino nurbs library.

You suggest to give a try to viacad, is difference so huge about filleting stuff. It happends in some case that I'm stuck
with some fillets, even if it happends less and less. And most of the time if a fillet failed in MoI, Rhino will not really help either.

Viacad pro seems to have some nice tools in :

http://www.punchcad.com/products/viacadpro_features.htm

- Bending Along Curve ... well why not (are they using construction history to handle this ?)
- Offset Surfaces : would it be a little better than MoI's one ?
- Skin with Guide Curves ... don't really get the concept
- Surface Matching ... sounds cool, and seems to be performed after the surface creation, not sure if it will work on imported models
- Tangent Covers ... well seems to be a patch tool right ?

Would like to have an advice about it, the workflow seems really different from MoI and I'm affraid by the learning curve :S

Michael
Sorry for being a pain.
I went through everything I thought I had learnt.
I tried all sorts of options.
And still can not get a fillet.

When you can spare a moment please.

Brian

Not an expert here,
But I suspect that this shading change result from a lost of continuity in the wing, and that give some trouble to build the fillet.


Looking at the profile curve of the wing, there is indeed probably a discontinuity in this area, the 3 points (red lines) should fit on one line.


So with the help guide, I draw a line going throuth the 2 first curve control points


and move the third one on the same line


I don't really get how you build the wings, so I reuse the 3 curves in the file, using the network ... seems to give something pretty close from
the original one


Now it's time to clean this part, separate everyting and delete the wing


Select the body and click on the show points command


Select the hole edge curve


and hit delete.


rejoin everything.


Don't forget to cap the wing with the make planar command


Booelan union


Fillet should work !


Sorry for all the spelling mistakes, did it really fast ;)

@Pac
In France Viacad is here ! http://www.cobright.fr/
Many video in French (more for Shark ) but it's same prog for basic functions!
Article on DVF http://www.3dvf.com/modules/publish/Logiciels_1895_1.html

The more important! Comparaison between all products!
http://www.punchcad.com/products/PunchCADFeatureCompareV1.pdf

Thanks Poilou for the the reference, the 3dvf review was instructive !

So I did a quick try in viacad, and the fact that I wasn't able to cross over the red line make me thing that was maybe the problem in MoI too.
Indeed I was able to come very close from what viacad can do on this particular shape -> 0.425 was the limit I find for this wing.

Heurm ... round 2 ... Via was able to do a little bit larger, but seems to add an extra edge too Oo



I think I'll stop here as :

-I'm talking to myself
-I'm starting to be a little bit lost too :P

Hi PaQ,

> As you're talking about it, will Viacad (pro) be a better alternative
> than rhino to extend my actuall MoI toolset ?

Well, it all depends on what you want to do.

Viacad would be better for things along the "Mechanical CAD" or "Solid modeling" direction (for example, shelling & fillets), while Rhino would be better for stuff along the "Industrial Design" and "Surface styling" type direction (flowing surface type stuff).

Neither one really covers the other area very well.


> For the moment I switch time to time to rhino for :
>
> - the surface continuity option with the sweep or network tool
> - the patch tool
> - sometimes to use the sweep tool when Moi's distribution
> failed to give a nice result.

This is the kind of surfacing stuff that would do better in Rhino. I think that some of this is present in ViaCAD as well, but is kind of like an afterthought over there and not really set up very well (in my opinion).


> As I'm still a noob in this cad world, I don't really get the
> difference between viacad and Moi/Rhino nurbs library.

Well, they all use different libraries. So they tend to have different sets of bugs and different weak and strong areas.

The one used by ViaCAD is used by many "parametric solid modeling" / Mechanical CAD programs though and has a lot more development time spent in the areas of filleting and shelling in particular.


> You suggest to give a try to viacad, is difference so huge about filleting
> stuff. It happends in some case that I'm stuck
> with some fillets, even if it happends less and less. And most of
> the time if a fillet failed in MoI, Rhino will not really help either.

No, it is not very likely that Rhino will help out for filleting. There probably are a few cases where Rhino could do a fillet where MoI had problems, but much more of the time I think it is the other way around where MoI handles fillets that Rhino has problems with.

And Rhino does not currently even have a shell function at all, so it is zero help for that. Shelling is a pretty good area of ViaCAD though.


> Viacad pro seems to have some nice tools in :
>
> - Bending Along Curve ... well why not (are they using
> construction history to handle this ?)

No, they use some code in the ACIS "Deformable modeling" library to do this, being able to bend things depends on a bunch of code that calculates the bent object, having construction history doesn't really have anything to do with it.

But this is an area that would probably be handled better by Rhino, that have a nice set of new tools in v4 for deforming objects.


> - Offset Surfaces : would it be a little better than MoI's one ?

Yup, this would be a strong area of ViaCAD.


> - Skin with Guide Curves ... don't really get the concept

I think it is their version of 2-rail sweep.


> - Surface Matching ... sounds cool, and seems to be performed
> after the surface creation, not sure if it will work on imported models

Should work fine with imported surfaces, but probably again I'd go for Rhino with this kind of "surface styling" oriented task.


> - Tangent Covers ... well seems to be a patch tool right ?

I think so.


> Would like to have an advice about it, the workflow seems really
> different from MoI and I'm affraid by the learning curve :S

Yeah, one downside of ViaCAD is that it is kind of based off of an older line of programs, it has a lot of legacy remnants in the way that it works. It would probably take a bit to get used to actually creating things from scratch in it.

I'd generally recommend to use it mostly for filleting and shelling pieces, if you just focus on those particular tools that would probably get the optimal use out of it with least frustration.

- Michael

Hi Brian, no problem. I'm sorry that filleting gives so much trouble it is unfortunately a quite sensitive and complex calculation involved with it.

It looks like PaQ has given some great steps above there for how to make a more totally "fillet friendly" shape.

I took a look at your model, and it actually your existing model seems to fillet ok for me at a small radius value like radius of 0.2 .


So after doing that, here is a look at that front edge that PaQ was referring to:



Zooming in:




You can see there that since those pieces do not meet smoothly, it forces the filleter to try and splice in a kind of corner connection piece between them. Making those smooth to one another will eliminate that and helps makes a more simple fillet structure there, that can help.

Then the other thing is notice how this "seam" edge is pretty close here:



Probably the #1 problem with fillets currently is that it will not cross a nearby edge like that, it will only approach it. So currently it tends to be best to make your part actually cut through the seam instead of come close to it, that avoids that issue.

- Michael

PaQ, Michael
Thanks for all that brilliant help.

WOW!

The study/think cap is going to be busy again today.

Brian

As a PS side note!

I saved the MoI file as an OBJ file and took it into a polly modeller to try filleting there.@#%&**

MoI is GREAT!

Brian