# Variable radius fillet near zero radius points - fillet is separate from polysurface

I am learning rhino and created a simple 2 rail sweep. One rail is along xyplane and the other along xzplane and intersect at a point on x axis. A smooth cross section curve starts at a point on 1 rail and ends on the other rail and is swept along both rails. The result is a polysurface that I mirror and join to create a closed polysurface with a bottom that is planar (along xy plane). I am trying to create a fillet on the bottom edge (planar). I know that the intersection of the rails causes the cross section to create a bit of a â€śpoleâ€ť where the zheight dimensions go to zero at that point. That is why I am using variable radius fillet(_filletedge) and setting the radius of that point to zero.
However, when I run filletedge along the bottom, a fillet strip is created but rhino cannot seem to trim the polysurface and leaves both the polysurface and the created fillet strip as separate objects when the command finishes (even though trim/join was set to yes). I am guessing that this is due to the point that goes to radius zero.

My thought was that I should use the fillet strip to trim the original polysurface but the fillet strip does not seem to intersect the polysurface (Zooming in, the fillet strip comes close and intersects at some points and not others by small tolerance amounts).
Question: In order to do a manual fillet I have to intersect the fillet with the 2 surfaces. The fillet strip just misses that surface by small tolerance amounts. Is there an easy technique to make this fillet strip (created with filletedge) to intersect with the 2 associated surfaces? Like extend edge to nearby surface?
Question: ultimately, I want to be able to fillet near a point with zero radius. Is there a simpler way than manually doing the fillets?

Can you upload an example file? Use the vertical arrow in the toolbar above where you type your post.

[quote=â€śvinchanity, post:1, topic:37928â€ť]
(Zooming in, the fillet strip comes close and intersects at some points and not others by small tolerance amounts)
[/quote]This may be due to too coarse a display mesh setting.

Hi David,

Ive uploaded the file and sorry if it is just an arbritary shape which is part of my lesson. Please note that I also tried to use the fillet strip to split the polysurface and it would not due to the areas where the fillet strip doesnâ€™t reach the polysurface.

It would appear that fillet can be touchy because sometimes when I do the filletedge rhino gives me an â€śinvalid geometry createdâ€ť and I press the report bug problem but then the result is that the fillet is performed with trim/join of the polysurfaceâ€¦albeit with some naked edges. If I donâ€™t get the invalid geometry created popup, then I get the situation shown in the file uploaded.
filletproblem.3dm (427.4 KB)

You should refine the mesh setting in DocumentProperties https://wiki.mcneel.com/rhino/meshfaqdetails That will not solve your problem but it will clean up some of the â€śgapsâ€ť which you are seeing.

Hi Vince - I think Iâ€™d make another less convoluted shape curve out near the tip to help control the sweep out there. FIlletEdge still does not want to trim on its own but you can trim by hand with the edge curves of the fillet surfaces.

filletproblem_PG.3dm (396.4 KB)

-Pascal

Thanks Pascal. Interesting. So you added a crosssection near the tip. I used this and had to use sweep 2rail twiceâ€¦once for tip and once for the body. Then made a solid and this time FilletEdge was able to trim and join?! I noticed however that the filletedge this time used 2 control points at the small tip cross section instead of 2 stacked control points at the tip. I think this did the trick. I uploaded my file. A couple questions.

1. Pascal, my question still stands regarding a fillet strip that doesnâ€™t quite intersect the surface at some points. Is there a way to â€śnudge growâ€ť the fillet surface to force an intersect or just to grow the fillet strip to intersect and trim?
2. how come my swept surface leaves an isocurve crosssection at the tip whereas, the one you did does not? Am I not using sweep 2rail wrong in having to do 2 commands (both sweep2rails) to do tip and body?

forgot to upload my fileâ€¦here it is.filletproblem_VC.3dm (667.9 KB)

Hi Vince - once should do it - use the Point option to force the sweep to converge on the tip, then add the cross section curves.[quote=â€śvinchanity, post:6, topic:37928â€ť]

1. Pascal, my question still stands regarding a fillet strip that doesnâ€™t quite intersect the surface at some points. Is there a way to â€śnudge growâ€ť the fillet surface to force an intersect or just to grow the fillet strip to intersect and trim?
[/quote]

Iâ€™d use the edge curves to trim. Since a fillet, naturally, just barely touches the surfaces, the intersection between the fillet and the surface can be spotty - trim fails. But if you force using the fillet edge curves, no surface-surface intersection is needed, the curve is pulled to the surface and the trim has a much better chance of working. Force usig the curve by

1. DupEdge first and use the curve to trim
2. Type CRV and Enter when trim asks for trimming objects, then click on the fillet edges - the CRV filter will ensure that the edge curve and not the surface are selected as the trimmer.

-Pascal

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Thanks for your comments David. The fillet strips genuinely did not intersect and it wasnâ€™t a display mesh issue. However, thank you for the great info on the display mesh adjustments. Iâ€™ll look through that.