3-2-1零件找正是建立零件坐标系的最基本又常用的方法。然而，在实践中我们曾多次发现一个不容忽略的找正步骤小误区。这就是喜欢测完全部找正特征后再创建找正程序，并称其“自动建坐标系”
然而，这种找正方式不是随便就可用的。因为，“自动建坐标系”是有条件的。
诸如上面的4种找正方法，若由于找正步骤不当，就可能影响到找正精度。理由是不建第1轴，那么用于旋转第2轴的直线和圆的测量就不可能有正确的投影平面。元素都测错了，建轴方向和原点还能正确吗？
两种方法如下：
一。分步建立坐标系
MODE/MAN
F(PLN1)=FEAT/PLANE,CART,31.5458,35.7296,0.0000,0.0000,0.0000,1.0000
$$ Measurement points are created through nominal points
MEAS/PLANE, F(PLN1), 4
PTMEAS/CART, 2.5609, 59.6350, 0.0000, 0.0000, 0.0000, 1.0000
PTMEAS/CART, 4.4214, 6.4864, 0.0000, 0.0000, 0.0000, 1.0000
PTMEAS/CART, 57.7665, 4.8560, 0.0000, 0.0000, 0.0000, 1.0000
PTMEAS/CART, 61.4343, 71.9410, 0.0000, 0.0000, 0.0000, 1.0000
ENDMES
D(CRD1) = DATSET/FA(PLN1), ZDIR
F(LN1)=FEAT/LINE,BND,CART,5.0291,0.0000,-2.2324,63.4836,0.0000,-1.7494,0.0000,-1.0000,0.0000
$$ Measurement points are created through nominal points
MEAS/LINE, F(LN1), 2
PTMEAS/CART, 5.0291, 0.0000, -2.2324, -0.0000, -1.0000, -0.0000
PTMEAS/CART, 63.4836, 0.0000, -1.7494, -0.0000, -1.0000, -0.0000
ENDMES
D(CRD2) = ROTATE/ZAXIS, FA(LN1), XDIR
F(PT1)=FEAT/POINT,CART,0.0000,5.1310,-2.5965,-1.0000,0.0000,0.0000
MEAS/POINT, F(PT1), 1
PTMEAS/CART, 0.0000,5.1310,-2.5965,-1.0000,0.0000,0.0000
ENDMES
D(CRD3) = TRANS/XORIG, FA(PT1), YORIG, FA(LN1), ZORIG, FA(PLN1)
$$ Set.CAD2PCS.CADM_1
二：投影平面：二维元素投影
即测量需要投影平面的特征时，就可在投影平面后面框中拖放实测平面，使其能按照正确的投影平面进行计算；
MODE/MAN
F(PLN1)=FEAT/PLANE,CART,36.3775,40.2480,0.0000,0.0000,0.0000,1.0000
$$ Measurement points are created through actual points
MEAS/PLANE, F(PLN1), 4
PTMEAS/CART, 62.1684, 72.2680, 0.0000, 0.0000, 0.0000, 1.0000
PTMEAS/CART, 14.7020, 76.9748, 0.0000, 0.0000, 0.0000, 1.0000
PTMEAS/CART, 8.5794, 7.5293, 0.0000, 0.0000, 0.0000, 1.0000
PTMEAS/CART, 60.0601, 4.2200, 0.0000, 0.0000, 0.0000, 1.0000
ENDMES
F(LN1)=FEAT/LINE,BND,CART,6.7136,0.0000,-2.6360,61.8148,0.0000,-4.3394,0.0000,-1.0000,0.0000
$$ Measurement points are created through actual points
MEAS/LINE, F(LN1), 2
PTMEAS/CART, 6.7136, 0.0000, -2.6360, 0.0000, -1.0000, 0.0000
PTMEAS/CART, 61.8148, 0.0000, -4.3394, 0.0000, -1.0000, 0.0000
ENDMES
F(LN_PROJ1)=FEAT/LINE,BND,CART,6.7136,0.0000,0.0000,61.8148,0.0000,0.0000,0.0000,0.0000,1.0000
CONST/LINE,F(LN_PROJ1),PROJLI,FA(LN1),FA(PLN1)
F(LN2)=FEAT/LINE,BND,CART,0.0000,5.7992,-2.1853,0.0000,57.2509,-2.7268,-1.0000,0.0000,0.0000
$$ Measurement points are created through actual points
MEAS/LINE, F(LN2), 2
PTMEAS/CART, 0.0000, 5.7992, -2.1853, -1.0000, 0.0000, 0.0000
PTMEAS/CART, 0.0000, 57.2509, -2.7268, -1.0000, 0.0000, 0.0000
ENDMES
F(LN_PROJ2)=FEAT/LINE,BND,CART,0.0000,5.7992,0.0000,0.0000,57.2509,0.0000,0.0000,0.0000,1.0000
CONST/LINE,F(LN_PROJ2),PROJLI,FA(LN2),FA(PLN1)
F(PT_INTER1)=FEAT/POINT,CART,0.0000,0.0000,0.0000,0.0000,0.0000,1.0000
CONST/POINT,F(PT_INTER1),INTOF,FA(LN_PROJ1),FA(LN_PROJ2)
D(CRD1) = DATSET/FA(PLN1), ZDIR, ZORIG, FA(LN_PROJ1), XDIR, FA(PT_INTER1), XORIG
D(CRD1) = TRANS/ZORIG, -0, YORIG, FA(PT_INTER1), XORIG, -0
$$ Set.CAD2PCS.CADM_1
