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

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

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.

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

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.

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

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.

Brandroid, 30 seconds to solve your problem! Blend G2 - 0.5




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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!

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)

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.

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.

Hello,

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

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