Fixed locating supports (rest pads)

Fixed locating supports (or rest pads) are usually hardened (case hardening steels ≈0.10% C) and ground finishing and small in size. The locating surface of the support will be milled (knurled - see figure above) or with round head (cylindrical connections - see figure below) in order to locate workpieces from unprocessed datum surfaces. To locate workpieces from processed datum surfaces needs flat-headed supports and supporting plates (see figure below). The reliefs between their locating pads provide space for chips and dirt as the workpieces are wrung onto the pads. The shaft-hub connection types are made a press fit in the body of fixture and are replaced when worn out.

Typical dimensions for fixed locating supports locating from flat datum surface (dimensions are in mm):

D=6-40;  d=4-25;  H=10-76;  h₁=6-40;  h₂=10-25;  R=4-40;  L=60-220;  w=16-35;

When designing a fixture with locating elements (flat head, round head, etc.) choose type, size and number accordingly to the maximum load P:

• For round-headed support of diameter D:
  D, mm  10   16   25   40
  P, KNt      2    5   12   30
• For milled-headed supports of D (or dimensions DxD):
  D, mm  10   16   25   40
  P, KNt     4   10   25   60
• For smooth surface supports and on supporting plates the maximum admissible load is 5 Nt/mm².

The above data holds for workpieces made from steel and iron. For nonferrous metals the maximum admissible load should be 30-40% less.