# Struggling to make a solid after boolean union

**URL:** <https://discourse.mcneel.com/t/struggling-to-make-a-solid-after-boolean-union/214880>\
**Category:** Rhino\
**Tags:** windows\
**Created:** [January 22, 2026, 12:21am UTC](https://discourse.mcneel.com/t/struggling-to-make-a-solid-after-boolean-union/214880 "2026-01-22T00:21:36Z")\
**Posts on this page:** 4\
**Page:** 1

<div class="post-metadata">

**Author:** ![Roy6](https://sea3.discourse-cdn.com/mcneel/user_avatar/discourse.mcneel.com/roy6/32/722092_2.png) [@Roy6](https://discourse.mcneel.com/u/Roy6)\
**Post date:** [January 22, 2026, 12:21am UTC](https://discourse.mcneel.com/t/struggling-to-make-a-solid-after-boolean-union/214880/1 "2026-01-22T00:21:36Z")

</div>

I have build this “lid” - I was not able to join the open polysurface, but I was able to “Union” the two objects (eye hook \> lid structure)

I need to turn this into a solid for 3D printing. Can you help?

[Create Solid Failure.3dm](https://discourse.mcneel.com/uploads/short-url/uNWOnhHDttFH82VVfvGxTQJDBnC.3dm) (696.3 KB)

---

<div class="post-metadata">

**Author:** ![Normand](https://sea3.discourse-cdn.com/mcneel/user_avatar/discourse.mcneel.com/normand/32/476050_2.png) [@Normand](https://discourse.mcneel.com/u/Normand)\
**Post date:** [January 22, 2026, 10:52am UTC](https://discourse.mcneel.com/t/struggling-to-make-a-solid-after-boolean-union/214880/3 "2026-01-22T10:52:43Z")

</div>

Hi @Roy6

Impossible to say where you went wrong, but there are a few minor mistakes. The trim curve for the bottom face of the upper part is bad, giving you naked edges. Untrim and re-trim to fix it. Also there are a lot of really skinny surfaces/slivers all over the model - see screen grab. Be careful of precision when building you curves and geometry!

 ![image](https://global.discourse-cdn.com/mcneel/uploads/default/original/4X/e/7/6/e767333a0cc9942f186cc2c9c5ac0b7603e2b620.jpeg)  
And then there’s an inside corner missing, which is easily mirrored from the other side. The existing corner has a small triangular overlap, which is easily trimmed away with the edge of the underlying surface. Here’s a closed solid for you 🙂  
[Create Solid\_JN.3dm](https://discourse.mcneel.com/uploads/short-url/qVgbY9D6U8l03ntMsE41kyE0oBe.3dm) (1.3 MB)  
HTH, Jakob

---

<div class="post-metadata">

**Author:** ![Roy6](https://sea3.discourse-cdn.com/mcneel/user_avatar/discourse.mcneel.com/roy6/32/722092_2.png) [@Roy6](https://discourse.mcneel.com/u/Roy6)\
**Post date:** [January 22, 2026, 11:04am UTC](https://discourse.mcneel.com/t/struggling-to-make-a-solid-after-boolean-union/214880/4 "2026-01-22T11:04:00Z")

</div>

Hi Jakob,

Thanks for replying. I actually managed to fix the issue thank you!

---

<div class="post-metadata">

**Author:** ![Normand](https://sea3.discourse-cdn.com/mcneel/user_avatar/discourse.mcneel.com/normand/32/476050_2.png) [@Normand](https://discourse.mcneel.com/u/Normand)\
**Post date:** [January 22, 2026, 11:04am UTC](https://discourse.mcneel.com/t/struggling-to-make-a-solid-after-boolean-union/214880/5 "2026-01-22T11:04:43Z")

</div>

Well done 🙂