If you built or are building the KRMx02 or any of the CNCRotuerParts machines you may want to upgrade your Z-axis 5-start ACME nut.
The new nut has an aluminum housing that wont distort so its much stiffer. It also has a steel spring for anti-backlash.
Here I am installing the new nut assembly on my KRMx02 build.
http://www.youtube.com/watch?v=QJxxAl_QW84]5 Start dumpsterCNC ACME Nut Assembly - YouTube
You can pick up one of the nuts here.
My KRMx02 Upgrade page can be found here:
KRMx02 ACME Nut Upgrade
Author of: The KRMx01 CNC Books, The KRMx02 CNC Books, The KRmc01 CNC Milling Machine Books, and Building the HANS Electric Gear Clock. All available at www.kronosrobotics.com