We are making a small update to our design rules for how to put multiple parts in a file. Ceramics does not have a start up fee, so it is ok to put multiple parts (non-interlocking) into one file. However, there are a few things you should keep in mind when you do:
Parts should not be nested
The longest dimension of all parts must be on the same plane
Individual parts in an STL should have bounding box where the dimensions add up to above 120mm.