Extrusion tapered incorrect

A problem for Rajaa.
I wanted to make a tapered extrusion; rhino apparently unable to do so, but at the red edge you determine a problem (if you zoom in on the red border you see the defect).
Whit Autocad this extrusion is successful, it keeps the red edge and perfectly closed surfaces.

You could check you?
Extrusion tapered incorrect.3dm (177.6 KB)

With autocad succeeds:

There are two things you are doing wrong.

First your tolerance is way too loose to create the features you want. You can’t make a .03mm wide surface with your tolerance set to .05mm

The other mistake is to use extrude surface command in the solids menu. Like most of the other solids tools in Rhino this will almost always produce garbage. The only time it will reliably work correctly is when the edges of the surface are composed of tangent lines and arcs.

If you want a correct result in Rhino then you have to use the surface modeling tools. This means extracting the edges and using ExtrudeCrvTapered and then extending the surfaces and trimming
and joining.

ExtrudeTaper.3dm (131.7 KB)

Apart from what you say is right, but I wanted a sharp edge (red border). Autocad manages to create this tapered extrusion, if you look in the video. The edge must be clean, not at 0.03.

I used the command extrusion tapered curve, but rhino fails to realize and close all surfaces (lacking the surfaces of red edges).
I wanted to make a sharp edge!

You need to explode the curves so that each is extruded individually and then do all the extending and trimming and joining the surfaces manually.

If you want it to come to a sharp edge then extrude the 2 surfaces that you want to come to a sharp edge high enough so that they intersect and then extrude all the other curves to that same z level as
the intersection. You can copy the bottom planar surface to that z level also to make the top cap. Then do all the extending and trimming and joining necessary to make it a closed solid.

Thanks Jim.
The problem is not to get what they want in manual mode, that’s easy to do with Rhino.
I opened an issue of command “Extrude tapered” because Autocad can do this and Rhino not.

It could be a bug to fix in the command?

It is definitely a bug and users have been complaining about it for at least 18 years.

Lots of users don’t understand that if you want things done correctly you are going to have to become adept at making things in manual mode.

I think is a simple bug to fix.
If someone spends money to buy a license is right that Rhino is able to perform certain simple operations, such as this one. We are not asking for anything complicated and impossible! They have solved the most difficult things

Making a calculation: 18 years means 3 versions of Rhino, it seems strange that in all these years some major bugs have been resolved.

Yes, but while making stuff manually is fine when you’re working on one object, when you have to automate stuff - a typical job for me might be making 500 -1000 of these tapered roofs at a time via a script, or even just a couple of dozen without a script - the “manual method” is simply out of the question.

The AutoCAD example simply shows the strengths of the ACIS solid geometry kernel which apparently has been designed to do this stuff…

–Mitch