donaldkwong 2017-3-6 08:23 edit
I spent a good chunk of time today trying to use the 9-point calibration to level out the build plate. For some reason, the right side of the build plate is off by about 1.6mm from the left side, which resulted in wavy rafts like this: http://imgur.com/H1tCYmE.
However, after multiple attempts and multiple scratches on the build plate, I wasn't able to completely fix the problem. That's when I decided to try to tackle it from the hardware side and ended up finding a way to fix it for good there. Here's a quick write up of what I did, in case it's helpful to others.
My goal was to get the y-axis arm to be parallel to the build pate, since that was where my offset was, and here's what I did:
Turned the power off, since I'm going to be relying on gravity to pull the y-axis arm down later.
Disconnected the extruder to give me more room to work with.
Loosened this bolt: http://imgur.com/X7Isrys. This will allow the right end of the y-axis arm to move up and down slightly. Mine was able to move almost a centimeter.
Placed a level on the build plate and let the y-axis arm rest on top of it: http://imgur.com/oKNnDlT. You can use whatever object you have available that is solid and square. This will make the y-axis arm parallel with the build plate.
Tighten up the bolt from step 3.
Reconnect the extruder.
After doing this, I reset the calibration offsets and just did a calibration on the #5 center point. Now I get nice, clean rafts on all 9 of the calibration points on the build plate: http://imgur.com/iwYfli9.