# Boolean union failure

**URL:** <https://discourse.mcneel.com/t/boolean-union-failure/219206>\
**Category:** Rhino\
**Tags:** mac, rhino8\
**Created:** [May 20, 2026, 9:58pm UTC](https://discourse.mcneel.com/t/boolean-union-failure/219206 "2026-05-20T21:58:29Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![Nico\_Salimena](https://sea3.discourse-cdn.com/mcneel/user_avatar/discourse.mcneel.com/nico_salimena/32/742742_2.png) [@Nico\_Salimena](https://discourse.mcneel.com/u/Nico_Salimena)\
**Post date:** [May 20, 2026, 9:58pm UTC](https://discourse.mcneel.com/t/boolean-union-failure/219206/1 "2026-05-20T21:58:29Z")

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Boolean union keeps failing on this file and i cant figure out why. Both are closed polysurfaces and the internal section was split by the curve of the exterior so they should be intersecting. anyhelp is appreciated

[shellsecond.3dm](https://discourse.mcneel.com/uploads/short-url/pGfdUrXa3F4cb4CnVnc5a5VaLhG.3dm) (14.2 MB)

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<div class="post-metadata">

**Author:** ![theoutside](https://sea3.discourse-cdn.com/mcneel/user_avatar/discourse.mcneel.com/theoutside/32/770924_2.png) [@theoutside](https://discourse.mcneel.com/u/theoutside)\
**Post date:** [May 20, 2026, 10:16pm UTC](https://discourse.mcneel.com/t/boolean-union-failure/219206/2 "2026-05-20T22:16:23Z")

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everything you need to know about why your boolleans don;t work can be reveled by running the **intersect** command on these two parts.

see the resulting curves- notice that they are not closed.

this means your intersections are not able to create a closed intersection which will immediately make a union fail.

To fix it, increase the overlap between your two parts so that they intersect completely. Either scale you inner part up a bit, your outer part down a bit or extend the “legs” of your inner part a bit so that they are a bit longer.

 ![image](https://global.discourse-cdn.com/mcneel/uploads/default/original/4X/2/6/3/2634dd519d0a2c7569d8b89f516aca88ff9de570.jpeg)

a tiny scale in the length and width made this work-

 ![image](https://global.discourse-cdn.com/mcneel/uploads/default/original/4X/7/d/c/7dcbeebab59e058e704d223601c3b2c8b52fd981.jpeg)