OK, it's not made of metal, but it does replicate a steam engine model. Ed Bertschy's Paper Steam Engine designed this years ago, but the link (on several sites) is dead. A friend, Bill Jones, in British Columbia too, found a copy on a backup disc and kindly sent it me to post. So - for all of you who have been looking for this too - here's a link to the four files which make up the package:
formatting link
great project to do with your children (or give them a copy while you work on yours).
Mike Gray in Beautiful British Columbia