[MrFlippant]

I've now added dwg, stl, obj, & 3ds files to the allowed attachments on the forum, so you should now be able to upload files in those formats. I'm away from home at the moment, so I haven't been able to check out whether it all works, and bizarrely obj and 3ds files still don't have a standard MIME type associated with them in spite of them having being around for donkey's years. So it's a bit of an experiment.

The file size limit is currently 5mb, but we'll see how this goes, and adjust if necessary.

3MF would be a worthy addition.