Keep in mind, while there are some known issues with printing on plotters, various improvements and fixes have already been implemented. Unfortunately, not all plotters can be tested. As a quick workaround, it is recommended to download and install PDF printer, print the model to PDF, and then send the PDF to the plotter.
But here are some configurations that should help with printing large diagrams, i.e. to plotter.
1. Install PDF printer. The PDF printer of my preference is PDFCreator (http://www.pdfforge.org/pdfcreator).
Then run Toad Data Modeler and open your model.
2. Click File | Page Setup... and select the printer to use (i.e. the PDF printer). Then set page size, i.e to Ledger or use Customize, depending on the printer options, and settings like enable "Fit to Page" and "Portrait" orientation options.
More information about page formats can be found at: http://en.wikipedia.org/wiki/Paper_size
3. Click File | Print... and uncheck options on the Settings tab (i.e. "Print Page Numbers" and "Print Frame").
4. Print the output and see result.
5. Zoom-in to see how graphics and fonts are displayed.
6. Then print out the PDF file via the PDF printer/viewer software. Most plotters are bundled with software that supports PDF format.