the reciprocal value of the stiffnessis calledflexibledegree C（mm／N）：
C?1Ksystem?YsystemFYAstheyaremeasuredunderstaticcondition,theyarealsocalledstaticstiffnessandflexibility.Staticstiffnessistheattributionoftheprocesssystemitself,itcanberegardedasindependentwiththeexternalforces.
（1）workpiecestiffness
the stiffness of regular and simple workpiece can be calculated with formula. For example, the slim shaft in Fig.6.12(a) is a simple support beam model,
FYx(L?x)Y??3EILwhereL——lengthoftheworkpiecemm；
22x——distancefromthecuttertotherightcentermm；E——materialelasticmodelN／mm2；I——inertial matrix of the section mm4。
（2）component stiffness of the machine tool
The clearance between the coupled parts will influence the deformation of the components, and finally influence the stiffness of the machine tool
Fig.6.13
1-center shaft, 2-force imposing device,3-force inspector,4-micrometer 5-force imposing screw
Fig.7.15 the static stiffness measurement of the headstock and tailstock
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