help with a new sharpener

I went to lowes to get a knife sharpener and got this.

I've tried it on some kitchen knives, and it seems to make an improvement, but on my dull folders they can not get paper shredding sharp, but close to it.
Is there any technique or style of sharpening for this that will get it very sharp?
Right now I am doing a couple passes on each end of the blade at a 20-30 degree angle, and its getting sharper, but once I reach that point where its almost paper shredding sharp, no matter how many times I try, the blade won't get any sharper.
All help appreciated!

Here's a page with videos on how-to sharpen.

http://www.dmtsharp.com/general/basicsharp.htm

You might want to look on bladeforums.com in this sub-forum for advice.

http://www.bladeforums.com/forums/forumdisplay.php?f=794

Keeping the angle consistant is one trick to getting a good edge. I use the lansky sharpening system as I am not good at maintaining a consistant angle freehand.

Yep, biggest things are to keep a consistent angle and to not use too much pressure.

Rod and Guide systems help to take the guesswork out of getting the right angle.