The spindle box adopt square ram. The Z-axis is four-face closed encircling sliding guide way. The guide way is cast iron bonding Turcite-B with better vibration damping to afford steady machining. It is especially suitable for spindle extension to make heavy milling, boring large holes and five-face machining with angular head. The inserted steel guideway realize anti-bending and anti-torsion of beam. The spindle saddle moving parts have guide way unload mechanism to reduce the sliding friction and benefit to increase the positioning accuracy.