1. Take care to level the machine properly. You will save a lot since you reduce wear of guideways significantly. And this is the wy to reach good accuracy.
2. Re-adjust ATC after the leveling. Simple to do and you will save a lot preventing your spindle nose againsta damage.
Questions:
1. Do you have the blue box with installation disquettes? Is it just Dutch or is English as well?
2. Do you have the OSP Data Management Card?
3. Have you the ( paper books ) manuals?
4. What is your tool shank?
Concerning suspicious spindle. Check the spindle run-out. Radial shuld be about 1?m.
I would check the mechanical condition of spindle first.
Concerning the ambient temperature. Shouldn't be the root cause in my opinion. Check your spindle cooling system.
Post note:
You are on the right path addressing this chat
Congratulations!