There are any number of web pages that demonstrate how to calibrate your extruder. Basically you will be heating everything up, making a mark on your filament 100mm up from the entrance to your extruder and then extruding 100mm using your control software. You'll measure how much actually extruded by measuring the mark on the filament and adjusting your e-steps until the amount you tell it to extrude equals the amount actually extruded. esteps can be adjusted by sending g-code commands. You don't have to reflash your firmware.

Here is a link to one set of videos: http://zennmaster.com/makingstuff/re...part-1-e-steps There are many more out there and maybe other folks will chime in with their favorites. It has been a long time since I learned how to do this so many more examples now.

BTW, if you haven't already, you should check your x,y and z calibrations as well. This is much different on a delta than on a cartesian bot. Google it and you will have plenty of examples to use.

You can actually hear your extruder skipping. It sounds like clicks and if you look close you will see the stepper kind of stopping and starting. Usually the print fails before completion when this is happening so maybe this isn't what is going on with yours.

Cheers,

KDog