# problem in using vtkextrusion for 3D files
**URL:** https://discourse.vtk.org/t/problem-in-using-vtkextrusion-for-3d-files/5236
**Category:** Support
**Created:** [February 23, 2021, 2:13pm UTC](https://discourse.vtk.org/t/problem-in-using-vtkextrusion-for-3d-files/5236 "2021-02-23T14:13:28Z")
**Posts on this page:** 2
**Page:** 1
### Author:  [@Amir\_Hossein\_Zeydi](https://discourse.vtk.org/u/Amir_Hossein_Zeydi)
#### Post date: [February 23, 2021, 2:13pm UTC](https://discourse.vtk.org/t/problem-in-using-vtkextrusion-for-3d-files/5236/1 "2021-02-23T14:13:28Z")
I used vtkextrusion to extrude a 3D STL of bone. But after using the code below it just duplicated it for me.
this is my code:
```
import vtk
filename = "the file"
#First STL file
reader = vtk.vtkSTLReader()
reader.SetFileName(filename)
extrude = vtk.vtkLinearExtrusionFilter()
extrude.SetInputConnection(reader.GetOutputPort())
extrude.SetExtrusionTypeToNormalExtrusion()
extrude.SetVector(0, 50, 1)
extrude.Update()
mapper = vtk.vtkPolyDataMapper()
if vtk.VTK_MAJOR_VERSION <= 5:
mapper.SetInput(extrude.GetOutput())
else:
mapper.SetInputConnection(extrude.GetOutputPort())
actor = vtk.vtkActor()
actor.SetMapper(mapper)
# Create a rendering window and renderer
ren = vtk.vtkRenderer()
renWin = vtk.vtkRenderWindow()
renWin.AddRenderer(ren)
# Create a renderwindowinteractor
iren = vtk.vtkRenderWindowInteractor()
iren.SetInteractorStyle(vtk.vtkInteractorStyleTrackballActor())
iren.SetRenderWindow(renWin)
# Assign actor to the renderer
ren.AddActor(actor)
# Enable user interface interactor
ren.ResetCamera()
iren.Initialize()
renWin.Render()
iren.Start()
```
and here is the output
---
### Author:  [@lassoan](https://discourse.vtk.org/u/lassoan)
#### Post date: [February 23, 2021, 4:36pm UTC](https://discourse.vtk.org/t/problem-in-using-vtkextrusion-for-3d-files/5236/2 "2021-02-23T16:36:33Z")
STL files cannot store surface normals. You need to insert a vtkPolyDataNormals between the STL reader and the extrusion filter. Note that you may get self-intersecting mesh near sharp edges. If you really need to grow a shell around the entire bone then it is more robust to do the margin growing on the segmentation and then convert to mesh.
If you plan to generate 3D-printable patient-specific surgical guides then you may be interested in participating in this project: [https://github.com/lassoan/SlicerBoneReconstructionPlanner](https://github.com/lassoan/SlicerBoneReconstructionPlanner). It is being actively developed, but we can already create surgical plan and generate cutting guides like this automatically:
