FIN surface at other angles

Hi, I have a double-curved, saddle-shaped surface and I would like to take the edge and extrude it relative to the surface normal. No problem, just use the “fin” command. But I also want to add a 5-degree draft angle to the fin as this will be for a mould. It would be great if the Fin command also had an angle option between 0-180 degrees. I can imagine doing this in GH but it would be hard to maintain tolerance efficiently. Does anyone know a native Rhino command that does this? Obviously the corners won’t match anymore, but I can manually resolve that.

The closest I can get is using Pipe on the surface edge, drawing the line profile at the correct angle and then doing sweep2 using the surface edge and the edge of the Fin. I can tell this isn’t accurate as the new surface edge doesn’t lie on the pipe. Essentially I want to rotate the edge of the Fin around the original surface edge and then loft.


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Hi Steven - the idea of an angle in Fin I understand, but associating a draft angle to Fin seems problematic since this angle has nothing to do, usually, with the surface normal that Fin uses. You can use ExtrudeCrv Tapered. Did I miss the point?


Hi Pascal, sorry I should have been clearer, what I want is the surface normal plus an angle; not a straight extrusion with an angle. This way you can choose any angle between the normal and the tangent. The following shows roughly what this might look like in GH. There’s a curve drawn on the surface and the script is generating fins at -45, 0 and 45 degrees to the normal of the surface. Would be nice if there was an equivalent in native Rhino.

Draft angles for moulding are not changing with surface normals and can be acquired exactly in the way Pascal suggested (extruding the edge in the desired direction).

Anyway the command you are looking for is part of the toolset of the Autodesk Shape Modeling plug-in.
Look for the “Flange” command (see picture)

No native Rhino solution and not exactly a cheap plug-in, I know.
But well worth a look and, if you have use for its whole feature set, well worth the money.

Cheers, Norbert

Thanks Norbert, yes that looks like what I’m after. I probably should’ve avoided using the word ‘draft’ as that seems to have caused some confusion. The thing is, we are making thin, curved architectural panels and as modeled, the sides are normal to the face. There is slight entrapment of the panels in the mould though, so we are just adding 5 degrees to the edges (from the normal) to help them out of the moulds. Hence, I would still call this ‘draft’. Would be good to add this to the wish list to expand the capability of the fin command please Pascal!

Hi Steven - I see, so the actual object would be made flat with the draft angle, and then curved on assembly, is that it, and you need to model the curved version?. One way would be to flow angled surfaces from a base plane to the target surface - trimming will require a dose of CreateUVCrv beforehand - see if the attached file helps.

DraftToNormal.3dm (238.0 KB)


Hi Steven,

you could try the MoveUVN Command. Turn on the points of your fin surfaces, select one point along the edges you want to change. Then _SelU to get all edge points selected. Now for example if you want to add 5° to a fin with a height of 100mm you’ll have to move the points along their normal vector for 8.75 mm (= tan(5)*100).

Enter 8.75 to _Scale in the MoveUVN interface and drag the slider to the limit in the direction you want.
No rocket science in precision but might work for you in this case…


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Thanks Pascal, yep that looks like a good work around!

I have and reread these posts and am still not getting it. Is the pull direction up or down on that part? Also does the 5 deg. Make the flange stlightly more or less than the surface? Thanks ,Mark

Hi Mark - the part is to be flexible and molded flat, but the user would like to model the part as installed, and not flat, is how I understand it.