There is an adjustment for skew, and I'm very familiar with both the Xerox 700 and the KM C7000 - you should be getting similar registration from both.
Please read through this thoroughly even if you've been walked through this process as there are small details that may be causing the issue you are having. Once you are familiar with it it will not take more than 5-10 minutes and you won't have to do it very often once it is set up properly in the media catalog. PM me with any questions.
The C6000/C7000 have the ability to tie all of the registration settings I'm about to walk through to individual media catalog entries. If you do not currently operate using a paper catalog I would suggest you set one up so you can save the proper registration settings for that paper.
In the PF602, loosen the side guides and place 5 or so sheets in the drawer and keep the drawer open - do not tighten the side guides. On the left side of the drawer, you will see a blue tie-down knob that can slide laterally inside a groove. When left loose, the knob will be forced to one side of the groove - slide it to the other side and tighten it to lock it in place. Close the drawer. You'll hear the tray raising up and once it does, open the drawer and it will be locked in the feeding position. Tighten the side guides to be firm enough against the sheets to not have any lateral movement if you place your hand on it and try to move it, but make sure it is not so tight that it is bowing the paper. Loosen the blue knob on the left side to drop the tray back down and load the rest of your stock. This will eliminate lateral movement or whipping at the feeding position.
Once the paper is loaded, go to the "Paper Settings" menu on the UI, hit "Change Set", and hit "Both Sides Adj". There are adjustments for Magnification, Image Shift, and Registration Loop which should all be set to 0 if you've never done this before. You'll see options for "Front" and "Back" along the top, keep it set on "Front" and hit "Chart Adjustment". On the next screen, select "Print Mode" on the bottom. You can select a quantity of sheets by using the number pad hard buttons below the touch screen on the UI - YOU MUST PRINT AT LEAST 3 SHEETS AND TAKE MEASUREMENTS FROM THE THIRD SHEET to properly adjust registration, as it takes 2 sheets to actively register to the paper position. Once the fuser comes to temp the "Start" button will turn blue, hit it, and grab the top sheet. With a mm ruler, measure each line to either where it intersects with the adjacent line or to the edge of the sheet if it does not intersect. Input these measurements and hit "Adjustment Start". This will center the image on the sheet and adjust for proper magnification of the image. When you get back to the Both Sides menu you'll see the 0's have been automatically changed to the proper adjustment.
From the Both Sides menu, hit the "Back" button and repeat the chart adjustment process. After properly centering and scaling the image with the front chart adjustment, the back chart adjustment will allow you to align the back side to the front side (its basically a cross hair in each corner and you input how far off the back is from the front on the X and Y axis in each corner). This measurement is additive, so if you don't get it right the first time you can print out another set of charts to tweak it further. If you can get one corner lined up and see skew in the other 3, move on to the Registration Loop adjustment below.
Once you get back to the Both Sides Menu, the last adjustment is the "Registration Loop" setting. The Registration Loop Adjustment will allow you to adjust skew. The registration unit has 2 sets of nip rollers - a drive roller that is continuously feeding into a registration roller that is timed to turn on and off intermittently. The timing is such that the drive roller will feed a sheet into the stationary registration roller which lags prior to feeding. As the drive rollers continue to feed against the stationary registration roller, it will cause the paper to "loop" or rise up in the center and snap perpendicular to the registration roller eliminating skew in paper. This concept is very similar to a gate system if you are familiar. When set at "0", heavier paper will simply pass through the roller system without snapping. If set too high, you will see wrinkling or jamming in the registration unit as the paper won't be able to feed through it, so you want to set it high enough to effect skew but not so high that the paper can't feed.
To save these to the paper catalog entry (as they will be different for 80# text vs. 100# cover for obvious reasons), hit "Register", pick the name of the paper you are working on if it is already created to overwrite it, or type the name of the paper if it is your first time, and save it. If you've done these adjustments and you still get poor registration, you need to escalate it through your local service department.
