A few things you might consider, If you only got a 6 degree rise in 20 min run time, that isn't much. You could most likely stand for a bit more bearing preload. Another question is what type of cutting tools are you using? If your using carbide insert type, try turning up the spindle speed, other wise use HSS, and make sure you tool is on cenre of coarse. You might want to go over the gib adjustment too, make sure everything is snugged up. The finish on your test cuts looks pretty rough, almost as your spindle speed is to low, and the feed is to fast. But, I would check all these things first.