# Offset Face / Surface Impossible?

**URL:** <https://discourse.mcneel.com/t/offset-face-surface-impossible/176818>\
**Category:** Rhino\
**Tags:** windows\
**Created:** [February 28, 2024, 7:44pm UTC](https://discourse.mcneel.com/t/offset-face-surface-impossible/176818 "2024-02-28T19:44:19Z")\
**Posts on this page:** 6\
**Page:** 1

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**Author:** ![PetrVacek](https://sea3.discourse-cdn.com/mcneel/user_avatar/discourse.mcneel.com/petrvacek/32/513119_2.png) [@PetrVacek](https://discourse.mcneel.com/u/PetrVacek)\
**Post date:** [February 28, 2024, 7:44pm UTC](https://discourse.mcneel.com/t/offset-face-surface-impossible/176818/1 "2024-02-28T19:44:19Z")

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Hello everyone

I was having a hard time offseting faces of a polysurface. This is why I want to share the issue with you to ask for your approach and ask McNeel whether it is possible to implement a different “Surface offset” library. Or what is the reason for such a huge difference between Fusion360 and Rhino? Maybe it’s just me and I am doing the whole thing wrong…?

The goal - create a casting mould. Shape created in Rhino, received as STEP. I have Rhino 8, exported as Rhino 7 file: [OffsetSurfaceRhinoFusion.3dm](https://discourse.mcneel.com/uploads/short-url/kFoBtnb9RbAp4T5Pll8oDz4BDoo.3dm) (477.7 KB)

**Steps to do:**

1. Offset sides +5 mm.
2. Offset the whole surface +5 mm and work with these shapes further (not important).

**Fusion approach - straightforward, easy, two steps.**

1. Offset sides  
 ![image](https://global.discourse-cdn.com/mcneel/uploads/default/original/4X/4/4/1/44154a3601d33693b953057c8255dae9597fcf9e.jpeg)
2. Offset the whole shape  
 ![image](https://global.discourse-cdn.com/mcneel/uploads/default/original/4X/a/4/b/a4b37ba56f354a69f261401e83666291ff0ce5ac.jpeg)

**Rhino attempt:**

1. ExtractSrf, Join - why is it not possible to extract surfaces joined?  
 ![image](https://global.discourse-cdn.com/mcneel/uploads/default/original/4X/a/3/1/a31f93005c109e27c9cc34ee5ec3fd9579531edd.jpeg)
2. OffsetSrf - resulted in somehow messy srf  
 ![image](https://global.discourse-cdn.com/mcneel/uploads/default/original/4X/b/f/e/bfe91fabd868b575e56c91b0e9e8356c2b190773.jpeg)
3. Boolean union (uuuf, this time it worked)  
 ![image](https://global.discourse-cdn.com/mcneel/uploads/default/original/4X/6/5/2/65227e706f9955c88099e572cdea521e2eedc729.jpeg)
4. Offset srf - waited almost 10 seconds for a result…wait…wut?? 🤯  
 ![image](https://global.discourse-cdn.com/mcneel/uploads/default/original/4X/9/2/8/92860c952e91e472655105719e83a3cb79fed579.jpeg)

Fusion result for comparsion 🤔

 ![image](https://global.discourse-cdn.com/mcneel/uploads/default/original/4X/4/d/9/4d97a5a9f90904e9229ee9ed4ecfee5cfc550347.jpeg)

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<div class="post-metadata">

**Author:** ![lander](https://sea3.discourse-cdn.com/mcneel/user_avatar/discourse.mcneel.com/lander/32/511244_2.png) [@lander](https://discourse.mcneel.com/u/lander)\
**Post date:** [February 28, 2024, 8:03pm UTC](https://discourse.mcneel.com/t/offset-face-surface-impossible/176818/2 "2024-02-28T20:03:03Z")

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> [@PetrVacek](#):
>
> what is the reason for such a huge difference between Fusion360 and Rhino?

fusion is a parametric solid modeler based on the cloud.

Rhino is a freeform surface modeler based on awesomness 🙂

> [@PetrVacek](#):
>
> why is it not possible to extract surfaces joined?

what?

> [@PetrVacek](#):
>
> OffsetSrf - resulted in somehow messy srf
> 
> ![image](https://global.discourse-cdn.com/mcneel/uploads/default/original/4X/b/f/e/bfe91fabd868b575e56c91b0e9e8356c2b190773.jpeg)

😂 interesting how it solved it tho 😅

> [@PetrVacek](#):
>
> Boolean union (uuuf, this time it worked)
> 
> ![image](https://global.discourse-cdn.com/mcneel/uploads/default/original/4X/6/5/2/65227e706f9955c88099e572cdea521e2eedc729.jpeg)

what lol

> [@PetrVacek](#):
>
> offset srf - waited almost 10 seconds for a result…wait…wut?? 🤯
> 
> ![image](https://global.discourse-cdn.com/mcneel/uploads/default/original/4X/9/2/8/92860c952e91e472655105719e83a3cb79fed579.jpeg)

lol dang 😂 😭

> [@PetrVacek](#):
>
> Fusion result for comparsion 🤔
> 
> ![image](https://global.discourse-cdn.com/mcneel/uploads/default/original/4X/4/d/9/4d97a5a9f90904e9229ee9ed4ecfee5cfc550347.jpeg)

fusion model looks like it’s hiding isocrvs 🧐 🤔

Found some naked edges

 ![image](https://global.discourse-cdn.com/mcneel/uploads/default/original/4X/a/6/d/a6d0a96ccb54e850bd38c0d657d7ef7848338a88.png)

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<div class="post-metadata">

**Author:** ![Gears\_Gears](https://sea3.discourse-cdn.com/mcneel/user_avatar/discourse.mcneel.com/gears_gears/32/695143_2.png) [@Gears\_Gears](https://discourse.mcneel.com/u/Gears_Gears)\
**Post date:** [February 28, 2024, 8:17pm UTC](https://discourse.mcneel.com/t/offset-face-surface-impossible/176818/3 "2024-02-28T20:17:43Z")

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Perhaps tolerance setting could be to blame?

Though unrelated, 🦏 \> confusion 360 🤪

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<div class="post-metadata">

**Author:** ![jim](https://sea3.discourse-cdn.com/mcneel/user_avatar/discourse.mcneel.com/jim/32/570126_2.png) [@jim](https://discourse.mcneel.com/u/jim)\
**Post date:** [February 28, 2024, 8:22pm UTC](https://discourse.mcneel.com/t/offset-face-surface-impossible/176818/4 "2024-02-28T20:22:06Z")

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> [@PetrVacek](#):
>
> **Steps to do:**
> 
> 1. Offset sides +5 mm.

The reason it fails for an offset value that is any bigger than about 2mm is that to do the offset to a sharp corner Rhino has to offset the surfaces and extend them then trim everything. The problem with your model is the trimmed spheres are arranged so that the extending must go past the singularity of the sphere and Rhino chokes on that.

If you untrim the spheres and rotate them 90 degrees and retrim so that the singularities are no longer involved, then offsetting by 5mm will work.  
[offsetx.3dm](https://discourse.mcneel.com/uploads/short-url/ncFpiKOBDfWbFHWRNix2Rg1EgJ7.3dm) (146.4 KB)

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<div class="post-metadata">

**Author:** ![PetrVacek](https://sea3.discourse-cdn.com/mcneel/user_avatar/discourse.mcneel.com/petrvacek/32/513119_2.png) [@PetrVacek](https://discourse.mcneel.com/u/PetrVacek)\
**Post date:** [February 28, 2024, 9:02pm UTC](https://discourse.mcneel.com/t/offset-face-surface-impossible/176818/5 "2024-02-28T21:02:08Z")

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That is a great insight, thanks.

Yet mi question is why Fusion can do this operation with ease, but Rhino can’t on the first try without sphere surfaces modification? This is what I would love to know and also hopefully see in a near future enhanced in Rhino…

By the way, I like using both softwares even tho my number one is Rhino. But for instance, making threads or simple mechanical assemblies Fusion is better to do in Fusion.

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<div class="post-metadata">

**Author:** ![jim](https://sea3.discourse-cdn.com/mcneel/user_avatar/discourse.mcneel.com/jim/32/570126_2.png) [@jim](https://discourse.mcneel.com/u/jim)\
**Post date:** [February 29, 2024, 12:11am UTC](https://discourse.mcneel.com/t/offset-face-surface-impossible/176818/6 "2024-02-29T00:11:32Z")

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> [@PetrVacek](#):
>
> Yet my question is why Fusion can do this operation with ease, but Rhino can’t on the first try without sphere surfaces modification?

Well, I already did explain. This is a special case. Its only on rare occasions that the extension of a surface runs into a singularity. Rhino doesn’t handle this special case very well. Fusion handles it better.

That said, I don’t particularly like how Fusion handles this special case. I don’t like what Fusion does either.  
The fact is that the result you get in Fusion chops the sphere’s offset surface into multiple pieces. That is completely unnecessary as the model I posted earlier demonstrates. Chopping the sphere up into pieces may or may not make any difference in the long run, but when it does cause problems down the road I like to have software that can deal with that contigency.

It is also a special case that the surfaces in your model with singularities happen to be spheres. If they were not spheres I very much doubt Fusion would do any better than Rhino in this scenario. Knowing what is beyond a singularity on a sphere is dead simple. In the general case what lies beyond a singularity is somewhere between difficult to impossible.