Offset and Trim to Create "Lip"

How to Create Lip.3dm (315.5 KB)
I need to create a “Lip” surface from the larger surface. I offset the inner curve 2 mm inward and 2 outward. Then I tried using trim or split to remove the outer sections leaving only a 4 mm wide lip. Nothing worked. Then I noticed some strange features on the inner and outer curves.

How to Create Lip.3dm (315.5 KB)

Hi Ronald - ‘lip’ seems a bit too open to interpretation - do you have an image that shgows the sort of feature you are after?


Hi Pascal,

The Lip will be used to hold the hatch in place. The attached file shows a completed hatch with lip.

How to Create Lip.3dm (766.8 KB)

Is this what you want? I used Trim with ApparentIntersections=No in 8.4.24009.13521

How to Create Lip DC1.3dm (2.1 MB)

Hi David … That is what I want, but I still cannot figure out how to use Trim with ApparentIntersections=No. When I try, the entire surface is cut away. Were were the specific steps you used to trim away the outer and inner surfaces, leaving just the lip?

@pascal Trim command in both V7 and V8 produce strange results when used to trim the surface in the file in the first post. (Not the file in the second post with the same name.)

Open the file.
Select the inner and outer offset curves.
Depending on the order of selection of the parts of the surface to be trimmed unusal results occur including:

or the entire surface vanishing.

I do not have time to pursue further.

Yeah, I don’t love the merged surfaces with the kink - I imagine that is causing some trouble - I’ll investigate… I split it up again and exploded and can trim the two surfaces OK.


Hi Ronald - something like this is what I think we are shooting for, correct? (half)




We are using a lip that extends 2mm under the aerostructure and 2 mm out of the aerostructure. The aerostructure is 1 thick. The hatch is 1 mm thick (same as aerostructure). The lip is 1.5 mm thick.

Split, explode, and trim sounds like the right approach. I will also try David’s suggestion with different orders of operation.

Normally we would offset the outer surface inward by 1 mm to create the aerostructure, extract the inner surface, project the 2-d hatch on the inner surface, trim the inner surface, select the edge, offset by 2 mm inward and outward and then offset inward by 1.5 mm to create a solid.

With this center section, the process does not work.

Completed Hatch, Lip, Pillars, and Posts.3dm (1.7 MB)
This is a completed hatch with lip, pillars, and posts.

How to Create Lip (3).3dm (776.0 KB)
This is the upper aerostructure (after offset the outer surface inward). If I could extract the inner surface, select edge, and join edges to form a curve, I could then offset by 2mm inward and outward to form the lip. So perhaps what I need help with is how to extract, split, explode, trim, and join the inner surfaces.

Here’s what I think I’d do - since the curvature is relatively slight I might just work with a flat rounded rectangle.- (if the design allows a vertical pull for the hatch)

Offset it twice.
Offset the outer surface twice as well, - wall thicknes and then 2x wall thickness.
Extrude all three rectangle straight through the surfaces. Now all the surfaces are in place that you’ll need

-it is a matter of chopping up all of this and re-joining the bits that make up the surfaces you need, deleteing the rest.

  • Pascal

Hi Pascal,

I think you are on to a great approach! I can use this approach to cut the opening, create the hatch, build the lip, and create the internal wing box.



Main Hatch With Lip.3dm (1.1 MB)
Using what I think was your method, the students were able to quickly create a hatch, hatch opening, and lip. Unfortunately the final step of BooleanUnion of the Aerostructure with the Lip failed for no apparent reason.