20
7.3 Usage of the reading microscope
7.3.1 There are 100 grid lines and numbers around the reading drum wheel, each grid for 0.005
mm.
7.3.2 The eyepiece has two blocks of glass, one with 0~8 digits, digital interval for 1 mm and the
other with a movable line.
7.3.3 Example: Brinell hardness test with
φ10mm
ball indenter under 29420N (3000kg) test
force
7.3.3a Put the hardness block or specimen which has Brinell hardness indentation on a stable
table and place the reading microscope on the hardness block or specimen, with the long
lens barrel faced to natural light or illuminated with light. Rotate the eye guard on the
eyepiece and make the indentation edge clear.
7.3.3b Use any digit on the fixed glass of the eyepiece as the starting line (case grid 2), hold the
reading microscope in position and then rotate the drum wheel so the filar aligns with
the other side of the indent.
7.3.3c Read from the eyepiece, the integer value is
6, 6-2 = 4mm, and accumulate the remaining
fraction from the dial. For this example, the
method is as follows: read from the drum
wheel, it’s 41 grids, and each grid for
0.005mm, then 41×0.005mm = 0.205mm, the
indentation diameter is 4mm+0.205mm =
4.205mm. Check the “Brinell hardness
control table”: 205HBW10 / 3000
7.3.3d If the right tangent edge of Brinell
indentation diameter is more than half
grid and the drum wheel is 36 grid, then
plus 0.5mm when calculating the
indentation diameter and the Brinell hardness indentation diameter is:
4mm + 0.5mm + (36×0.005) mm = 4.68mm.
Fig.7
