@chris fullmer said:

My guess is that the faces are too small. You might try scaling everything up by 10 or 100, then scale it down afterwards. Can you upload the model here?

You are so right!! I drew a bolt of 10 meters and it worked fine.
The only hitch was sketchup itself. It crashed while scaling it down.
But it has a nice autosave, so ...
This was my result.
It's cool!!!

This is too small to start

Hai Chris
First I must say I am impressed with your work on Sketchup. I was very enthusiastic about your Shapebender. But I stumbled on some problems with it. I tried to make a “real” metric bold; a M10. That’s a 10mm bold with a thread of 1.5 mm /turn. I wanted to use the method of “fret2424” (http://www.youtube.com/watch?v=MKrWDNDd62c )
So I started with half a circle with a radius of 5 mm and I lifted one end 0.75 mm. That is not exactly right, but it was just to try.
I got some very strange results you might like to investigate.
Perhaps I am doing something wrong, but then I would like to know what.
Thanks