# Creating Joints on assembly meshes

**URL:** <https://prepomax.discourse.group/t/creating-joints-on-assembly-meshes/2139>\
**Category:** General Questions\
**Created:** [November 2, 2024, 7:29pm UTC](https://prepomax.discourse.group/t/creating-joints-on-assembly-meshes/2139 "2024-11-02T19:29:32Z")\
**Posts on this page:** 1\
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**Author:** ![Sound\_Spinning](https://yyz2.discourse-cdn.com/free1/user_avatar/prepomax.discourse.group/sound_spinning/32/4239_2.png) [@Sound\_Spinning](https://prepomax.discourse.group/u/Sound_Spinning)\
**Post date:** [November 16, 2024, 1:45pm UTC](https://prepomax.discourse.group/t/creating-joints-on-assembly-meshes/2139/23 "2024-11-16T13:45:26Z")

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Hi there,

I tested last year extensively exactly what you are after: assemblies in structural FEA in Calculix.  
It won’t do it as a general method for assemblies & joints.

If you read the ccx help docs carefully, you’ll find that the couplings (2 x types):  
‘soft’ [RBE3 (Nastran) or distributing (Abaqus)] &  
‘rigid’ [RBE2 (Nastran) or kinematic (Abaqus)]  
don’t handle properly rotations / moments for both loads and constraints, or merged at ref\_nodes to other mesh.

That means that all joints will be incorrect as a general method, only translations will be handled.  
But it gets worse: Calculix, I believe, doesn’t handle either 6DoF\_springs [CBUSH (Nastran) & connector cartesian+rotation (Abaqus)].  
This means that we cannot connect reference nodes on pairs of couplings with 6 K values for rivets, bolted areas, etc.

Even if you try beams instead of 6DoF\_springs they’ll disconnect the rotations at the shared reference node on couplings either end. Some codes have MPCs, but these will most likely over-constrain the model up at some DoF with some assumed inf. stiffness; they can also fail later when moving into non-linear FEA.

Below is a fig showing a tiny test model with a bearing and a shaft that Calculix couldn’t handle, while all other commercial codes will do via couplings + 6DoF\_springs.

 ![image](https://global.discourse-cdn.com/free1/uploads/prepomax/original/2X/d/df8fd23148efe66b6bfab80dc2c27fcbff97088a.jpeg)

I’ve recently reviewed all this for structural assemblies with joints (only way to build realistic FEA models) with several open source FEAs and none of them do it, except code\_aster.

I hope this helps.

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