# Offset surfaces gives me naked edges

Hello.

I am doing an offset surface (solid) and just realised the model has several naked edges.

Is this related to the tolerance ? I used 1 in order to get the same results to my original surface (single span).
I noticed that if I leave the tolerance 0.0001 my offset surface gets much more iso-curves. Not a problem with that, just that the filleting of edges gets really hard to control.

I guess Its a matter of trial an errors, but I wanted to know the theory/concept behind it.

Thanks a lot

Hello- for the naked edges, it’s impossible to say without a file… Offsets in general, except for special cases - planes, cylinders, spheres, are more complex than the input - there is usually no offset that has the same structure as the input so the offset needs to be fit to a tolerance.

-Pascal

Thanks Pascal. I figure it out that the reason of my naked edges was that I extended surfaces after offset them.
When using extend surface all my edges moved. I guess has to do with the option “smooth” activated.

The second question, If I may, is: Why my “offseted surface” gets shorter than my “original” one.

I understand the offset uses the normal directions of the original sfc, but in this case the “offseted srf” should be aligned in my Z axis. I will try to make a sample in Rhino since I can not share my actual model (unfortunately).

Thanks a lot for clarifying (always).

Edit: Please find the screenshot showing the difference between original and offeseted alignment.

In general an “exact” offset surface of a NURBS surface will not be a NURBS surface. (There are some exceptions such as those which Pascal mentioned.) That is how the basic math works. The tolerance option in NetworkSrf lets the user trade how close the result is to the exact offset surface and the number of control points.

A solid in Rhino is a collection of surfaces with edges that coincide (within the absolute tolerance) with another edge which are joined together. When OffsetSrf is used with a looser than default tolerance the edges of adjoining offset surfaces may not be close enough to be joined

Thanks David. My question is, for ex, why the line is not straight. I am not using solid. I am offseting a surface. Shouldn’t the line be still 90 degrees ? If you check my screenshot you can see how the second surface…has a line that is not coincident with my 0 axis.

Without a .3dm file with your geometry it is difficult to determine what is happening. You can post the file by either clicking on the vertical arrow icon above where you type a post, or by dragging the file into the area where you type.