How do I shell this model?

Hi,

I'm facing some problems with the shell function. I'm trying to shell this model I made of a styrofoam packing.

I want to shell it from the bottom (bottom face is face to remove)

For some reason it doesn't work.

- I tried extruding an extra bit on the bottom of the model, but that didn't help.

- I checked the minimum radius of curvature, which is 0.419616 mm. What should I do with it?

What do I need to change to shell this object?

thanks,

Jip

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