Filament gaps, and inconsistent under extrusion  

Filament gaps, and inconsistent under extrusion

For the benefit of others, here is my issue that took a week to figure out.

I printed a new extruder housing for the MK2 after having printed a perfect one once before. The second one was crap. Under extrusion all over the place. Printed Jeff's 75x75 calibration surface and it was near perfect. Print it again and stringy lines that pulled apart. This continued over and over. One good, two bad.

So, I installed a new nozzle figuring I had clogging issues. Just as a precaution I also installed a new piece of PTFE tubing. Nothing worked. I gave up for a few days and contemplated possible other issues. I printed another 75x75 calibration surface that had numerous random gaps. I was about the tear down the entire extruder housing again when I noticed a grub screw had fallen out and was on the counter. It came from the heater block and was the screw that holds the temperature thermistor in place. BOOM, problem fixed. The loose thermistor caused who knows what type of temperature swings that was causing all of my problems. Thank goodness the grub screw fell out. I am not sure how long it would have taken me to figure out trying to tighten it as a possible fix. I had tried just about everything else, but this screw being tight had not crossed my mind.

A tightening of this screw and all is well again.