Thanks for the replies. I followed up Zeamon on YouTube and found this video:
He has made a 3D pdf of his orrery which can be downloaded and explains how to view it in Adobe. It can be downloaded here:
http://www.zeamon.com/download/ZeamonOrrery.pdf
I never realised you could use Adobe in this way. It's really clever but not much help if your trying to build one. I've looked but can't find a set of 2D drawings in the 3D pdf. Can anybody who is familiar with 3D drawing tell me if it's possible to extract a set of dimensioned 2D drawings from the 3D pdf?
Thanks,
Alan C.