Often a spindle requires a “kiss” or “breeze” grind. This is a light grinding that does not require subsequent plating and regrinding. Just enough material is removed to correct minor imperfections. This is most often done on ID tapers and shaft faces to ensure perfect tool holder interface. If the spindle taper does not exactly conform to the tool holder taper, the tool may be able to move slightly. This can cause poor part quality and bad tolerance. A perfect match is an absolute must for high quality machining. Verifying taper quality at HST is SOP.