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How to set up a custom user defined paper size for your inkjet printer with Photoshop CS5 CS6 CC on a Mac
For Red River Paper greeting cards, scrapbook 12x12 sheets, panorama printing, and other special projects, you need to define a custom paper size in the Epson printer properties.
HANDLING 13x38 and 6x38
Newer OSX versions, 10.6 and up, have issues with handling custom sizes correctly. If your printer prints only a portion of the image, the image but in a smaller form, or will not print at all, you likely are seeing a custom paper size error.
For 13x38 or 6x38
Set paper width to 12.95"
This avoids problems with the 3800/3880 max print length of 37.5". You'll still have room for a full 12x36 or 5.5x36 print.
Margins must be set to 0.2" or larger. Smaller numbers may result in OSX designating your size as a roll and the printer will not print.