# Problem with creating surface by 'comp' command in CGX

**URL:** <https://calculix.discourse.group/t/problem-with-creating-surface-by-comp-command-in-cgx/116>\
**Category:** CalculiX GraphiX\
**Created:** [August 12, 2020, 1:47am UTC](https://calculix.discourse.group/t/problem-with-creating-surface-by-comp-command-in-cgx/116 "2020-08-12T01:47:20Z")\
**Posts on this page:** 1\
**Showing post:** 10

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**Author:** ![Tombs42](https://avatars.discourse-cdn.com/v4/letter/t/43a26b/32.png) [@Tombs42](https://calculix.discourse.group/u/Tombs42)\
**Post date:** [July 24, 2026, 1:14am UTC](https://calculix.discourse.group/t/problem-with-creating-surface-by-comp-command-in-cgx/116/10 "2026-07-24T01:14:26Z")

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Hi @fethio,

I’m glad to be able to maybe contribute. From the documentation, I understand that there are two ways. But, as you mentioned, they are all a relative displacement between the split surfaces.

The first is to apply a constant force using Cload to the node using PRE-TENSION. For example:

Let’s say that the top is SSurface\_from\_nodes.

\*PRE-TENSION SECTION, SURFACE=SSurface\_from\_nodes, NODE=Ref\_Node  
0., 0., -1.  
…  
\*Cload  
Ref\_Node, 1, 490000.0

Secondly, apply a displacement with a fixed Boundary, using the previous step with op=MOD.

\*PRE-TENSION SECTION, SURFACE=SSurface\_from\_nodes, NODE=Ref\_Node  
0., 0., -1.  
…  
\*Boundary, op=MOD  
\*Boundary  
Ref\_Node, 3, 3, 0

I have used both. First, in the second step of my analysis, I applied force and displacement to simulate other loads applied to the structure. However, I’m still working on it to achieve better results.

This example was the best for me: [Bolted Connections - #5 by JuanP74](https://calculix.discourse.group/t/bolted-connections/2548/5)

Please let me know if this answers your question, and we can discuss finding a better solution.

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