Octagon-cutting may reflect very comprehensively the displacement precision of machine tool coordinates, the stability of guide wheel revolution, the X, Y system return difference and the fidelity of feeding and actual displacement. Any problem related to the precision of machine tool can be incarnated while cutting octagon, which is unable to be concealed artificially.

The octagon cut should be analyzed according to the following several aspects:

1 The two straight faces parallel with X axis, have smaller size and low feeding speed, showing that the guide wheel axial shakes quite a lot, the joint-cutting becomes bigger.

2 The two straight faces parallel with Y axis, have smaller size and low feeding speed, showing that the guide wheel radial shakes quite a lot, the joint-cutting becomes bigger. 

3 The two parallel inclines of 45°, have smaller size, showing that the Y axis system return difference is big, the D-value is about as two times as return difference.

4 The two parallel inclines of 135°, have smaller size, showing that the X axis system return difference is big, the D-value is about as two times as return difference.

5 The 45°and 135°inclines appear washboard stripe which takes the lead screw pitch as cyclical, the X or Y axis appears distortion of the feeding displacement, showing that the working end surface of X or Y axis that the lead screw impels the carrier appears beats and distortion. This kind of relation between texture and cyclical can be only discovered in 450 and 1350 inclines.

6 The washboard strip on 45°and 135°inclines takes the electric machine gear as cyclical, showing that the electric machine gear is nonuniform or off-center, this kind of problem can not be seen while cutting straight line and also cutting circle can not distinguish its cyclical relations.

7 The washboard stripe on two straight faces which parallel with X axis is heavy, showing that the wire doesn’t walk along one path in the direction of Y axis when moves up and down. (The elongation line of "V" shape groove of up-down guide wheel is not a beeline, therefore while the wire reversing, the cyclical washboard stripe occurs.)

8 The washboard stripe on two straight faces which parallel with Y axis is heavy, showing that the wire doesn’t walk along one path in the direction of X axis when moving up and down, the tension has big difference when moving up and down. (Therefore while the wire reversing, the cyclical washboard stripe occurs.)

9 The angle by the incline with 45°and incline with 135°is over or less than 90°, showing that the verticality of X, Y guide rail is bad, which creates that the four straight faces are not vertical by each other but the two opposite faces can be parallel, its D-value is about as two times as the verticality error in this stroke.

10 Both up and down ends of cutting face are inconsistent, showing that the "V" shape groove of one of the up-down guide wheel for locating molybdenum wire obviously become bad.

As the above statements, octagon-cutting is truly a good means to examine the comprehensive precision of machine tool, any other shapes of cutting are very difficult to expose these syllabify. But determine the precision of machine tool with octagon-cutting, must pay attention to the following points:

a. Prevent the distortion of cutting route or material itself.

b .Mark the cutting direction and upper and lower face.

c. Any craft parameter or conversion speed can not be adjusted during octagon cutting.

d. Complete it in one time, the engine can not be closing down on the midway.

e. Proofread the molybdenum wire, guarantee its verticality.

f. It’s prohibitive to establish the gear backlash and clearance expiation.