The process to create a pre-designed 3d product is as follows:
1. Duplicate your base 3d model (so that you retain a 'clean' version for future use / duplications)
2. To check the print dimensions, edit the product and go to the Print Area Section. The print dimensions are given in mm in the print width and print height text boxes. (see image below)
3. Upload a 300dpi image file at those dimensions under the Artwork Tab (see Fig 1.). This file should match the print dimensions specified in the print area. Make sure to use transparency where necessary (particularly if the 3d model has been set up with colour change).
Important Note: Once the artwork file is uploaded, make sure that you tick 'Update Texture / View Background' before you click save so that the texture that the 3d model uses is stamped with the artwork and will be seen by the user on-screen.
4. Add any image or text personlisation areas to match the artwork (if necessary)
5. Print test the model so that what the user sees on-screen is reflected in the final print output.