Page 299 - Modular design for machine tools

258 Engineering Design for Machine Tool Joints

Frequency, Hz
270 180
90 30
16
12 Shaped
temp. 27°C
8
4

0
75 125 188 250 312 375
160 Ground
Joint stiffness 10 6 lbf/in 120 temp. 25°C

80

40

0
75 125 188 250 312 375

160
Scraped
120 temp. 24°C

80
40

0
170 281 422 563 704 845
Joint preload, lbf/in 2
Corrected for material stiffness, cast iron, dry, area 36 in 2
Figure 6-30 Relationships between joint stiffness and static pre-
load when excitation frequency is varied (courtesy of Thornley).

2. Lubricants. When there is oil between the joint surfaces, the in-phase
and quadrature components increase in all the cases, although their
rate of increase depends upon the surface topography, oil viscosity, joint
material pairings, static preload, excitation frequency, and hardness
of joint material. Figure 6-31 shows the marked effect of the oil on
the dynamic joint stiffness. The higher the oil viscosity, the higher
stiffness. It is, however, difficult to have the clear tendency for the
effect of each kind of oil.