Hooray! Extrusion now realized.

Thanks for your advice TIG, much appreciated.

Summarising:

1. All Profiles and Rails must be welded curves - even straight lines must be converted.
2. Use plugin weld.rb to weld
3. Convert a straight line to a welded curve by select > divide > segments ~30 > weld
4. For small objects best to scale up > process/extrude > scale down.

Having some difficulty with this plugin (in Extrusion Tools).

It will not let me select the profile in the attached file (the narrow ends) - will let me select the long edges OK (my intended rails) but this is not much use. Have no idea what the issue is - have also updated SketchyPhysics as there was a comment that earlier versions of this caused a problem.

Any thoughts appreciated, its driving me nuts!

Off_the_Rails.skp