Inward thickening

[jean.thil]

One can get inward thickening by offsetting a surface with a negative value.
The problem is that if there is a thin part, instead of just filling in the offset, Freecad create protruding stuff outside the original surface (look at the tail of my tadpole). I do understand that this behavior is the exact translation of « thicken my stuff » but this is not what I want, and I guess what would ask most of the users in a similar situation. Is there a way to get rid of this unwanted part of the volume ?

TIA

OS: Debian GNU/Linux 8.7 (jessie)
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.17.9766 (Git)
Build type: Unknown
Branch: bspline_stage1b_2017
Hash: 4b501f23288d6ba33f36aa8314fc0621092013c7
Python version: 2.7.9
Qt version: 4.8.6
Coin version: 4.0.0a
OCC version: 7.0.0

[microelly2]

The simplest way is to create a outward thickness too and subtract it from your part

[jean.thil]

Thanks.
I will try it

[jean.thil]

I tried it but didn't succeed.
I made an outer offset. The picture below shows the state of the screen during the dialog for creating the second offset.

tadpole_two_offset.jpeg (37.09 KiB) Viewed 2691 times

When I subtracted the outer offset from the inner, the operation failed.
I guessed this is because the two extrusions have a common face so I tried to use a intermediary offset (tadpole_3_offset) but it failed two.

[NormandC]

Your profile is a closed B-Spline with a very pointed end. It's not easy to offset such a profile and it seems like OCC can't handle it.

In the commercial CAD program I use at work, when I create an offset of a B-Spline curve, the resulting B-Spline has an extremely high number of poles, much higher than the original.

[microelly2]

what you need is a function like erosion in image processing
http://docs.opencv.org/trunk/d9/d61/tut ... l_ops.html

I wonder if this is already is implemented for point clouds in FreeCAD.
Discretize the curve, create a closed face
discretize it to get the inner bound

[NormandC]

The solution is Part 2D Offset! (new in 0.17)

FC017_jean.thil_tadpole_01.png (21.31 KiB) Viewed 2657 times

1. Use 2D Offset on Sketch
2. Extrude both Sketch and Offset2D object with solid option enabled
3. Apply Part Cut
4. Voilà

Thanks go to DeepSOIC for adding this tool.

[microelly2]

The solution is Part 2D Offset! (new in 0.17)

thank you for this tipp.one more very useful tool.

[Willem]

I was not aware of the 2D offset function either. I think it is not logical that this function is not located in the Sketcher and/or the PartDesign workbench, the logical workbenches for 2D functions, but in the Part workbench, which is the ultimate 3D workbench

[jean.thil]

Thanks for your help. It works for this example because the shape is an extrusion of only one profil. If the shape were a loft or a sweep of non constant profile, the 2D normal to the profile wouldn't be the same as the projection of the 3D normal to the surface. I'd like to find a way that works for most shapes. I have tried some other way but without success.