As the spindle rotation accuracy is not high and its bearing slide rail surface shape error institutions such as the motion of the beating occurred , the cutting process inhomogeneity and cutting materials such as discontinuities caused by fluctuations will involve cutting tool, the workpiece shift change, thus the thickness of the cutting , the cutting force or cutting width is changed , so in many cases, these factors may induce the unstable self-excited vibration from the processing system , the amplitude of the relative change in position is more enlarged , which affects knife back to eat the amount of change , so that the surface roughness increases.

It can be seen , to reduce the surface roughness , the area must be reduced residual eliminate BUE scales and spines to reduce the plastic deformation of the workpiece material and the cutting process of the vibration , in order to reduce the residual area , the tool should be compared large nose radius , the smaller angle deputy ; especially the sub angle of 0 ° wiper , very effective in reducing the surface roughness ; but wiper not too long, otherwise it will cause vibration , but the surface roughness increases, generally as long as slightly larger than the amount of feed can . In addition, there is a tool wiper wiper must ensure that the machined surface parallel with the installation , otherwise ineffective.

Rake angle generally have little effect on roughness ; But for large plastic material , the use of large rake angle of the tool is to reduce BUE scales and spines , thereby reducing the surface roughness of effective measures . For example broaching 1Cr18Ni9Ti stainless steel broaches, rake angle from 10 ° ~ 15 ° to 22 , the surface roughness can be reduced to Ra2.5 ~ 1.25um from Raum

And cutting edge flank surface roughness , roughness has a direct impact on the workpiece surface. As the tool surface roughness is reduced, help reduce friction and thus inhibit BUE scales and spines generation, therefore , the degree of growth BUE is different ; therefore all material between the tool and the workpiece material large friction coefficient, bond in serious cases, the surface roughness on bigger. When cutting carbon steel, under otherwise identical conditions , in accordance with the high-speed steel cutting tools , carbide cutting tools , order or titanium carbide -based ceramic cutting tools carbide cutting tools , workpiece surface roughness in turn decreased. But after a high-speed steel cutting tools TiN coating reduces the coefficient of friction and adhesion between the workpiece material and make BUE with barbed scales significantly reduced , thus significantly reducing the surface roughness .

Furthermore, strong wear of the tool will also increase the surface roughness ; particular boundary wear on the secondary cutting edge , on the machined surface roughness is more serious.