The Epson V7000 default media size contains implicit margins, built into the media size:
These are okay for regular printing, but with double sided printing these can cause a 5mm discrepancy between the A & B side, when the sheet is turned or tumbled.
If you want to print double sided, you should create a new media size without built-in margins. To do this:
1. Select the printer with the cursor in your RIP:
2. Go to File -> Output Device -> Edit Media Sizes...
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3. Click the + button:
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4. Create a media size with margins at zero- > Click OK.
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5. Restart Layout: Now this newly created media size will be available in the drop down menu: