William,
I could reach for my calculator to make the imperial>metrics>imperial conversions but I won't.
Estimated, if I have a 609 mm wide roll , set the normal printing mode not borderless, there will be 5 mm printer margin at the sides so a usable size of 598x430 mm if I create a print page size in the HP PCL3 driver of 608x440mm (I always use 1 or 2 mm less than the official inch widths). This will give an inch paper waste at the width and 10mm paper waste in the roll length, in total. On long runs of the same sizes I might nest more images on one print page, reducing the 10mm per image on the length of the roll to 0, not the first and the last image of course that still has a 5 mm print margin at leading or trailing edge. Or give at least some slack that I can cut Qimage's edge marks off instead of through the middle. Manual trimming afterwards then.
If you do not use the (defualt) automatic roll cut setting in the driver, some margin is added when you hit the cutter button on the printer panel. You could move the paper backwards first from the printer panel but it will be a hit and miss operation as it adds that extra margin nevertheless. You could make two markings at the front of the printer and move the paper back that distance. Probably taking more time than manual trimming.
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Met vriendelijke groet, Ernst
http://www.pigment-print.com/spectralplots/spectrumviz_1.htmApril 2014, 600+ inkjet media white spectral plots.