That is true, the machine does not have an DADF unit, which means you will have to turn the paper around and run it through the machine once more, though it will combine the output for you.
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The 6505dn comes equiped with the duplexing unit - it prints double sided document without any issue.
However, it does not copy double sided documents to double sided, even though I follow instructions in the manual.
The link you provided was how to make double sided prints - not double sideded copies.The following link says it is not supported: http://www.support.xerox.com/support/workcentre-6505/support/enus.html?objGUID=8154
Thank you for using the Support Forum. Please make sure that you have the optional duplex unit installed. If you have the duplex unit installed follow the instuctions in this solution to make a duplex copy. If you do not have the optional duplex unit installed then please follow the instructions in this soltuion for manually duplexing. If none of this information helps please consider contacting your support centre for further assistance.
Does the WorkCentre 6505dn support copying double sided documents? It has the menu option, but when I select it (either flip on short or long edge), it only copies the one side.