How to do two sided copies - Sharp AL-1641CS All-In-One Laser Printer

Two sided copying... When copying from one-sided originals to two-sided copies, copying orientation can be selected between Turn on Long Edge and Turn on Short Edge...... When making two-sided copies from the document glass, the paper size must be letter...Non-standard size paper cannot be used...When making two-sided copies, the multi-bypass tray cannot be used...... A A... A A... Turn on Long Edge Turn on Short Edge... Select two-sided copy mode.
When copying in a one-sided to two-sided mode:
Use the original to copy key to select the desired one-sided to two-sided
copying mode (Turn on Long Edge or Turn on Short Edge) Using the document glass
1 Press the start key.
The original is scanned into the unit's memory and the number of the
copy quantity blinks in the display.
2 Place the original that you wish to copy onto the rear side of the
paper, and press the start key again.
Copying begins.
Using the SPF
Press the start key. Copying begins in the selected two-sided copy mode.

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Thanks, Joe

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On page 52 and on page 53 of this pdf manual you will find your answer.

http://files.sharpusa.com/Downloads/ForHome/HomeOffice/PrintersFaxMachines/Manuals/cop_man_AL1641CS_1631.pdf