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Google Sketchup free 6.4.112

new try
Now I have made that
Erase the Up and down facetts rounded
then select for up and down the outlined internal then Planar = only one "facet" for each up & down
Export SKP
Result :in Sketchup all is fine except the Uper face is inversed so inverse it and all is fine

Are you sure of the construction of your Cylinder?