# Problem with Boundary Layer (Bolt Connection) **URL:** \ **Category:** Bug Reports\ **Created:** [February 22, 2022, 9:15am UTC](https://prepomax.discourse.group/t/problem-with-boundary-layer-bolt-connection/74 "2022-02-22T09:15:31Z")\ **Posts on this page:** 14\ **Page:** 1
**Author:** ![PhilippTheEngineer](https://avatars.discourse-cdn.com/v4/letter/p/3ab097/32.png) [@PhilippTheEngineer](https://prepomax.discourse.group/u/PhilippTheEngineer)\ **Post date:** [February 22, 2022, 9:15am UTC](https://prepomax.discourse.group/t/problem-with-boundary-layer-bolt-connection/74/1 "2022-02-22T09:15:31Z")
Hi all, there is a Video on YouTube showing a bolted connection. I redesigned the example and wasn`t able to create the boundary layer for the section. ![image](https://global.discourse-cdn.com/free1/uploads/prepomax/original/1X/56ed20a5eb3c14a198103219dcfc08c6fea67be3.png) When you open the pmx try to create a boundary layer on the white screw part : ![image](https://global.discourse-cdn.com/free1/uploads/prepomax/original/1X/4c7820f229142403bf367d99d21a12238c77028e.png) Prepomax gives me the error " The given Key was not present in the diccionary" Try for yourself and let me know if i miss something I also did the example from the YouTube video and there I was able to create Boundary layers on both sides of the section cut. However in my example it is not working. I also experienced this issue with big assemblies with more than one screw. .pmx Data (PrePoMax 1.2.0): [ScrewedConnection.pmx](https://prepomax.discourse.group/uploads/short-url/AeKiqLVe7NGWUZbOycBede4qJnY.pmx) (1.6 MB) ---
**Author:** ![FEAnalyst](https://yyz2.discourse-cdn.com/free1/user_avatar/prepomax.discourse.group/feanalyst/32/688_2.png) [@FEAnalyst](https://prepomax.discourse.group/u/FEAnalyst)\ **Post date:** [February 22, 2022, 12:55pm UTC](https://prepomax.discourse.group/t/problem-with-boundary-layer-bolt-connection/74/2 "2022-02-22T12:55:42Z")
I’ve checked your model and here are some notes: - it works for the upper region of the screw - each region of the screw has a different mesh since they are separate parts. I merged them into a compound part (like in Matej’s video) but the same error still appears. - it seems that your model was imported as an STL file, I would try with STEP format too This indeed seems to be a bug. ---
**Author:** ![PhilippTheEngineer](https://avatars.discourse-cdn.com/v4/letter/p/3ab097/32.png) [@PhilippTheEngineer](https://prepomax.discourse.group/u/PhilippTheEngineer)\ **Post date:** [February 22, 2022, 1:11pm UTC](https://prepomax.discourse.group/t/problem-with-boundary-layer-bolt-connection/74/3 "2022-02-22T13:11:24Z")
Hi Jakub, thank you for your insights. I used an step file, unfortunately i cant upload it here because it is not supported. I got this error quite often in assemblies, so i think it is a general bug. Maybe you can further look into it Best regards ---
**Author:** ![FEAnalyst](https://yyz2.discourse-cdn.com/free1/user_avatar/prepomax.discourse.group/feanalyst/32/688_2.png) [@FEAnalyst](https://prepomax.discourse.group/u/FEAnalyst)\ **Post date:** [February 22, 2022, 1:31pm UTC](https://prepomax.discourse.group/t/problem-with-boundary-layer-bolt-connection/74/4 "2022-02-22T13:31:39Z")
It should be possible to upload ZIP files here so you could add your STEP model in such format. ---
**Author:** ![PhilippTheEngineer](https://avatars.discourse-cdn.com/v4/letter/p/3ab097/32.png) [@PhilippTheEngineer](https://prepomax.discourse.group/u/PhilippTheEngineer)\ **Post date:** [February 22, 2022, 1:33pm UTC](https://prepomax.discourse.group/t/problem-with-boundary-layer-bolt-connection/74/5 "2022-02-22T13:33:08Z")
Thanks for the tip ! The step is attached here : [Bolting\_two\_flanges\_test.zip](https://prepomax.discourse.group/uploads/short-url/dinkjp2omfojwWI8mGkCr4TTfAs.zip) (6.3 KB) ---
**Author:** ![FEAnalyst](https://yyz2.discourse-cdn.com/free1/user_avatar/prepomax.discourse.group/feanalyst/32/688_2.png) [@FEAnalyst](https://prepomax.discourse.group/u/FEAnalyst)\ **Post date:** [February 22, 2022, 2:08pm UTC](https://prepomax.discourse.group/t/problem-with-boundary-layer-bolt-connection/74/6 "2022-02-22T14:08:19Z")
I can confirm that the same behavior is observed for the STEP format. However, it still might be a fault of CAD software. I wonder why it’s hollow after import. Can you say more about the geometry preparation process - which program did you use and how did you prepare the model for export (especially how did you split the screw into 2 separate parts) ? ---
**Author:** ![PhilippTheEngineer](https://avatars.discourse-cdn.com/v4/letter/p/3ab097/32.png) [@PhilippTheEngineer](https://prepomax.discourse.group/u/PhilippTheEngineer)\ **Post date:** [February 22, 2022, 2:13pm UTC](https://prepomax.discourse.group/t/problem-with-boundary-layer-bolt-connection/74/7 "2022-02-22T14:13:37Z")
I also checked the .Stp and it`s not hollow at all at when i import it. 🤔 Could you provide a screenshot ? The Software i used for geometry preparation was Siemens NX and i used simple planes to split the solid in two parts… Best regards ---
**Author:** ![FEAnalyst](https://yyz2.discourse-cdn.com/free1/user_avatar/prepomax.discourse.group/feanalyst/32/688_2.png) [@FEAnalyst](https://prepomax.discourse.group/u/FEAnalyst)\ **Post date:** [February 22, 2022, 2:23pm UTC](https://prepomax.discourse.group/t/problem-with-boundary-layer-bolt-connection/74/8 "2022-02-22T14:23:50Z")
> [@PhilippTheEngineer](#): > > I also checked the .Stp and it`s not hollow at all at when i import it. 🤔 Could you provide a screenshot ? Sure, here’s how it looks like on my side: ![hollow](https://global.discourse-cdn.com/free1/uploads/prepomax/original/1X/40372ba8b56e59fd993d4ffe59f682b0d07166a2.png) ---
**Author:** ![PhilippTheEngineer](https://avatars.discourse-cdn.com/v4/letter/p/3ab097/32.png) [@PhilippTheEngineer](https://prepomax.discourse.group/u/PhilippTheEngineer)\ **Post date:** [February 22, 2022, 2:31pm UTC](https://prepomax.discourse.group/t/problem-with-boundary-layer-bolt-connection/74/9 "2022-02-22T14:31:58Z")
As you might know the Section Cut which is implemented in Prepomax is not able to show solids correctly. This is the normal view you get when you have solids. When you mesh the parts and cut it afterwards then you will see a closed surface Best regards ---
**Author:** ![FEAnalyst](https://yyz2.discourse-cdn.com/free1/user_avatar/prepomax.discourse.group/feanalyst/32/688_2.png) [@FEAnalyst](https://prepomax.discourse.group/u/FEAnalyst)\ **Post date:** [February 22, 2022, 2:39pm UTC](https://prepomax.discourse.group/t/problem-with-boundary-layer-bolt-connection/74/10 "2022-02-22T14:39:11Z")
I almost never use the Section Cut tool before meshing (after that there are no problems with such visualization) and I thought that it used to show solid geometry correctly but I can be wrong. FreeCAD has the same effect with cut views. Anyway, the problem with boundary layer appears to be a bug so let’s wait for Matej’s response. ---
**Author:** ![Matej](https://avatars.discourse-cdn.com/v4/letter/m/a698b9/32.png) [@Matej](https://prepomax.discourse.group/u/Matej)\ **Post date:** [February 23, 2022, 7:28am UTC](https://prepomax.discourse.group/t/problem-with-boundary-layer-bolt-connection/74/11 "2022-02-23T07:28:11Z")
The section cut feature in the Geometry module is working as described. It only cuts the geometry and does not create a filled surface for the solid parts. It is a missing feature not easy to add. On the other hand the prismatic boundary layer obviously has a bug. This feature is quiet complex in order to keep all other geometry features such as vertices, edges and surfaces and visualisation items numbered with the same ids. I will try to fix it as soon as possible. ---
**Author:** ![PhilippTheEngineer](https://avatars.discourse-cdn.com/v4/letter/p/3ab097/32.png) [@PhilippTheEngineer](https://prepomax.discourse.group/u/PhilippTheEngineer)\ **Post date:** [February 23, 2022, 8:16am UTC](https://prepomax.discourse.group/t/problem-with-boundary-layer-bolt-connection/74/12 "2022-02-23T08:16:33Z")
Hi Matej, thanks for the reply. To fix the section cut in the Geometry module is not that important i think. The prismatic boundary layer is very useful, so an fix would be highly appriciated. Best regards ---
**Author:** ![Matej](https://avatars.discourse-cdn.com/v4/letter/m/a698b9/32.png) [@Matej](https://prepomax.discourse.group/u/Matej)\ **Post date:** [February 23, 2022, 7:56pm UTC](https://prepomax.discourse.group/t/problem-with-boundary-layer-bolt-connection/74/13 "2022-02-23T19:56:27Z")
Ok, I have found the bug. The problem was bigger than I thought and hidden in the function that imports the mesh after meshing the geometry in PrePoMax. It had no connection with the prismatic boundary layer directly. It also caused other problems that prevented some edges to be selected properly and maybe some problems that I am not even aware of. That is why I will release an updated 1.2.0 version of the PrePoMax tomorrow (1.2.1) with only this bug fix. ---
**Author:** ![Matej](https://avatars.discourse-cdn.com/v4/letter/m/a698b9/32.png) [@Matej](https://prepomax.discourse.group/u/Matej)\ **Post date:** [February 23, 2022, 7:56pm UTC](https://prepomax.discourse.group/t/problem-with-boundary-layer-bolt-connection/74/14 "2022-02-23T19:56:31Z")