larger print problems

Any advice on printing larger stuff. For some reason as the print goes on when it gets to about an inch or 2 above the plate it drags a lot on the surface of the print then dragging the print off the table. Is there something I'm missing?

 

I came here looking for an answer to the same problem and found a few posts in troubleshooting. Haven't tested any of the recommendations yet.

Can't post links, but titles and poster to follow; search Extruder Drag and should be in first few pages.
Extruder drags through print - Craig Muth
Z not raising during printing - Dan Smullen

 

sounds like the bed is sagging in the middle.. when printing very long items any sag is very big deal.. I had a .1mm difference in the middle than the ends.. I created this to fix it..

http://www.thingiverse.com/thing:1190174

see the washers, I ground down the face of the top one to get the perfect height.
The 8mm bar was left over from when I extended my bed to 330mm http://www.thingiverse.com/thing:1154745