Fillet trouble on converging edges

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 From:  Branden (BRANDROID)
6479.1 
Seems to be a common theme with me and MOI, but I can't get a fillet to calculate on the edges shown. I've tried tiny values and all the different types. I'm guessing MOI doesn't like the area where the two edges converge on the sides of the solid. Any obvious fixes that I'm missing here?





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 From:  Michael Gibson
6479.2 In reply to 6479.1 
Hi Brandroid, yes the fillet engine in the geometry library that MoI uses has a lot of trouble with this type of "disappearing fillet" type case where one side not only converges together but also is converging to a shared tangent area.

My best advice is to get ViaCAD to help out with these kinds of fillets, its fillet engine tends to handle this stuff much better. Export your model out to an SAT file, then import it into ViaCAD, and then bring it back into MoI. ViaCAD is available for $99: http://www.punchcad.com/p-9-viacad-2d3d-v8.aspx .

That would certainly be the easiest and most time effective method.


A couple of things that might help in MoI - the scale of the object is getting kind of small, that can be problematic when pieces that need to be generated are particularly small in size, say less than about 0.05 units or so, and also I'm not sure if the 2 halves of your object are fully smooth where they meet up, when you have 2 surfaces coming together which approach pretty closely to being tangent to one another but are actually about 3 to 5 degrees or so off from tangent that tends to make for filleting difficulties as well since it tends to require little slivery juncture pieces between fillet segments. Fillet surfaces only naturally join up end-to-end along fully smooth edges.

You've also got an area that's got a tight bend in the surface already, sometimes things like that can tend to be better to leave as sharp edges initially and then use filleting to round them off as well rather, you may be far enough away from that area right now, but trying to put an additional fillet that has to turn around a tight bend can also be problematic as well.

Those are some general tips, but I would really recommend seeing if you can just import into ViaCAD and get your fillet job done there and then bring it back into MoI.

- Michael
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 From:  Michael Gibson
6479.3 In reply to 6479.1 
I'm also not entirely sure what kind of shape you're really hoping to end up with at the convergence side...

A regular fillet is going to eat up a whole lot of space from that lip area - you may be looking for something called a "variable radius fillet" where you can give different radius values at different spots along the edge rather than having the whole thing done as one single radius.

Moi does not currently have a variable radius fillet method in it, so that's another thing you'd want to go into ViaCAD to do as well.

- Michael
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 From:  Michael Gibson
6479.4 In reply to 6479.1 
Yeah you might be looking for a "variable radius fillet" here, if you want the fillet to shrink down as it approaches that converging area.

With a regular fillet, the fillets from both sides will collide into one antoher some distance from that, see the attached 3DM file.

I constructed these fillets using surface/surface filleting, that's where you can break your model down into individual surfaces and then select 2 surfaces a time to fillet, rather than selecting edges.

Surface/surface filleting can sometimes help to construct some fillet surfaces to use for further construction where the edge-based filleter gets confused. But you then have to manually deal with trimming things up and also filling in corner juncture areas where fillets collide into one another.


But anyway, if you wanted something where the fillets shrink down to little pointy ends rather than just running into each other as in the attached model that would be a variable radius fillet that you'd want there.

- Michael
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 From:  Michael Gibson
6479.5 In reply to 6479.1 
I'm not entirely sure if it's what you're looking for, but I've attached here a version with those surface/surface fillets from the previous post above trimmed into place, then with a 2-rail sweep used to fill in the juncture area.

- Michael
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 From:  Branden (BRANDROID)
6479.6 In reply to 6479.5 
Thanks Michael, as always, your explanations are very helpful to understanding my problem. I was right in assuming that the junction of those edges was my problem area. The second file that you attached (mq-8b_top3.3dm) was quite close to what I was hoping for. I was able to recreate the surface-to-surface fillet you created in your first example (had no idea I could do fillets like this). However, I'm not sure how you did the subsequent trim and sweep to fill in that triangular patch. Can you elaborate on those two steps a little?

Cheers,
Branden
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 From:  Michael Gibson
6479.7 In reply to 6479.6 
Hi Branden,

> However, I'm not sure how you did the subsequent trim and sweep to fill
> in that triangular patch. Can you elaborate on those two steps a little?

There were a few kind of tricky steps along the way there.

First of all when doing the surface/surface fillet generation it will try to trim the surfaces but in this case makes a bad trim, so you only want to keep the fillet and not any modification to the surface. You do that by selecting the fillet, doing Ctrl+c to copy it to the clipboard, and then undo to restore things to their previous state, then do a paste. You can use this sequence "copy, undo, paste" anytime you want to preserve just one piece of a generated result but not any other modifications that happened.

After doing that on both fillets, you now have 2 fillet surfaces, one of which extends a ways past the other. You need to trim the longer one so that it ends at the same spot. This is done by selecting it and using the Trim command, with the Isocurve option. That allows you to pick one of the surface's own U or V directions as the cutting location, this works well for cutting fillets since one of those directions is the rounded direction. Snap the isocurve cutting location onto the spot where the fillet edges intersect with one another, and discard the excess end. Now you have the fillet surfaces all set up, the remaining thing is to trim a hole in the main object to make room for them.

The tricky part about the trim is that you have to cook up some kind of shape from the converging point onto the ends of the fillet. I decided to use curve blending to do this - in order to do curve blending between the edges of the fillet and the edge that ends on the converging point, you need to duplicate the edges to have regular curve objects, because if you try to run blend on edges it will generate a surface/surface blend. Curve blends are only generated between 2 "standalone" curves, not between 2 edges. So I duplicated the edges into regular curves by selecting them and doing copy / paste. Then I selected the ends of those curves and did Construct > Blend to make a smooth blend between them. Then switched to the top view and grabbed a corner of the edit frame and squished them down to be planar with "flat snap". Then used Construct > Curve > Project to project those now-planarized curves onto the surface to be cut. With that done that now fills in the empty space so that there is now a boundary that runs across the entire area so it can now be trimmed to that boundary.

So quite a lot of stuff going on there, let me know if you are stuck at any of these steps and I can explain that one in more detail yet.

- Michael
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 From:  Branden (BRANDROID)
6479.8 In reply to 6479.7 
Thanks Michael! Those steps worked perfectly. I was able to recreate your work easily. I've got to learn to start approaching NURBs modeling like this when I hit these roadblocks.
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 From:  Barry-H
6479.9 
Hi,
I have added a blend option for this problem that's not to complicated.
First split the edges you need to fillet at the point you wish the fillet
to start to taper.
Draw a circle the radius you require and sweep the edge you want
the fillet to be constant. Now sweep the edge to taper and add the
option for pointy end.
Trim using the sweeps and then blend faces of the constant edges.
The pointed end is then trimmed back to this position and the profile
of the blends and connecting flat face are used to sweep into the
corner.
Barry-H












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 From:  Branden (BRANDROID)
6479.10 In reply to 6479.9 
Thanks Barry. Always nice to have more than one approach to solving these sorts of things. I was able to create much of what you have in your example. For some reason though, I'm getting some pinched edges at the tip of that triangular patched area. Tried this a couple times and got this result each time. It looks like you've got better edges in your example.









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 From:  Barry-H
6479.11 
I joined the blend edges and the straight and swept it with the 2 rails
with the maintain height unchecked (see photo)
It also works as a network.
Barry-H
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 From:  OSTexo
6479.12 
Hello,

You might want to try no having the fillets converge at a point, rather carve out your desired curves and create a network patch at the pointy end of the fillets, allowing the patch to end it.
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 From:  Andrei Samardac
6479.13 
Brandroid, 30 seconds to solve your problem! Blend G2 - 0.5




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EDITED: 4 Feb 2014 by ANDREI SAMARDAC

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 From:  Branden (BRANDROID)
6479.14 In reply to 6479.13 
Andrei, thanks for the video. I think I tried this approach earlier on, but I wasn't getting good results. The difference was that I was trimming away a larger portion of the surface before blending. The trim I made was a segment all the way through the back of this solid. When I blended, I got some lumpiness on the back where the flat plane blended with the top. Your trim yielded a better blend, although I wasn't able to join the resulting surfaces into a solid. I made an adjusted trim line and blended that, and I was finally able to get a solid in about 30 seconds of work. This piece has been a headache, but I've learned a lot!
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 From:  Andrei Samardac
6479.15 In reply to 6479.14 
Brandroid I did not understand you, you could not join model using my method? I joined it in video and made solid everythink was ok)

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My Portfolio: www.samardac.tumblr.com
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 From:  BurrMan
6479.16 In reply to 6479.15 
ANdrei,
In your video, you did not trim the top surface "all the way back"... You started at the back seam edge.

When he trimmed it all the way back, he was having issues.

The 2 surfaces at the back (converging area) are not really tangent, or equal, so the blend back there is producing the poor results.

He fixed it by trimming out a larger portion of the top, AND bottom. That is kindof "hiding" the stressed surface.

The best thing would be to re-create that object, and have the back "converged" area come from "one initial piece". Either the bottom piece, or the top piece. One or the other.
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 From:  Branden (BRANDROID)
6479.17 In reply to 6479.16 
BurrMan is right, although initially I replicated everything Andrei did in his video. My first trim line was the same as his, and still I could not get a solid after blending the resulting surfaces; only a joined surface.

Then I cut through entire piece above and below the lip and got an acceptable result.
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 From:  OSTexo
6479.18 
Hello,

The back edges of the original model are not fitting too well, rebuilding the base model from scratch leaves a better end result.

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 From:  Andrei Samardac
6479.19 
Good, understood.
I made new tutorial about Collapsing fillet (disappearing fillet). You can check it here:
http://moi3d.com/forum/index.php?webtag=MOI&msg=6058.30

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My Portfolio: www.samardac.tumblr.com
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A lot of my Tutorials!
-----------------------------------------
Russian community of MOI 3D: www.vk.com/moi3d
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