The CUPS drivers that come with the printer include a utility for adding custom paper sizes.
Open a terminal and type:
brpapertoollpr_ql570
And you will see the usage examples for adding and removing custom sizes:
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LPRng Paper Size Tool (v 0.1) Copyright by 2005
Usage: brpapertoollpr_xxxx -P QL-xxxx Printer Name [-n add a Lable Format Name (<=32 bytes) -w Media Width(unit:mm) -h Media Height(unit:mm)]/[-d delete Lable Format Name]
For example:
1. Add a new Label Format with "New Label Format" name and 29mm width and 70mm length:
"brpapertoollpr_ql570 -P QL-570 -n New\ Label\ Format -w 29 -h 70" [enter]
2. Remove the Label Format with "New Label Format" name:
"brpapertoollpr_ql570 -P QL-570 -d New\ Label\ Format" [enter]
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As an example, I did
brpapertoollpr_ql570 -P QL-570 -n long_label -w 62 -h 200
to set up a custom paper size called "long_label" which prints on 62mm continuous roll, a 200mm long label