Hi John
I hope you have managed ok today with your blade settings. Although the 680 is 180-200 micron thick, it is still quite a soft vinyl so when ever we have cut it on our flat bed plotters we have not needed to alter the blade depth too much.
I am not too familar with the settings of drum plotters but the way we test cut is to cut a small 20mm sq box with a 5mm inline a close to the edge as possible, we weed this and then alter the blade to suit (I hope that made sense!!!)
Sorry I can’t be more help to you than that. If the job you have been doing is needing the extreme of your vinyl then you could possibly get a A4 sample piece added to an order do test cuts on.
Gill