Grinding wheels
A 46 K 5 V is an aluminium oxide wheel of F46 grain (medium), grade K (soft), structure 5 (52 % grain by volume) in a vitrified bond. Type the marking from a wheel’s label, with or without spaces, and each position is read: the maker’s own type and bond codes too, and a maximum operating speed. Give the wheel’s Ø and the speed for the fastest the spindle may run: a 300 mm wheel rated 50 m/s, 3,183 rpm.
The drawing magnifies the wheel: the grains at the grit’s size, packed to the structure, held by bond as firm as the grade.
A 46 K 5 V- A
Aluminium oxide
For steels; makers sell several varieties under their own type symbols.
- 46
Grain size F46: medium, grains about 370 µm
The F number of the sieve series: a higher number is a finer grain.
- K
Grade K: soft
How firmly the bond holds the grains, A the softest, Z the hardest. Grades are not the same from one maker to the next.
- 5
Structure 5: about 52 % grain by volume
The spacing of the grains, 0 the densest: a higher number has more pore room for chips and coolant.
- V
Vitrified bond
How it’s calculated
with the rim speed v in m/s and the wheel’s Ø D in mm. Grain content by volume is 62 % at structure 0, 2 % less for each number up (50 % at 6).
| Grain size | Band | Grain, about |
|---|---|---|
| F5 | coarse | 4.13 mm |
| F6 | coarse | 3.46 mm |
| F7 | coarse | 2.90 mm |
| F8 | coarse | 2.46 mm |
| F10 | coarse | 2.08 mm |
| F12 | coarse | 1.76 mm |
| F14 | coarse | 1.47 mm |
| F16 | coarse | 1.23 mm |
| F20 | coarse | 1.04 mm |
| F22 | coarse | 885 µm |
| F24 | coarse | 745 µm |
| F30 | medium | 625 µm |
| F36 | medium | 525 µm |
| F40 | medium | 438 µm |
| F46 | medium | 370 µm |
| F54 | medium | 310 µm |
| F60 | medium | 260 µm |
| F70 | fine | 218 µm |
| F80 | fine | 185 µm |
| F90 | fine | 154 µm |
| F100 | fine | 129 µm |
| F120 | fine | 109 µm |
| F150 | fine | 82 µm |
| F180 | fine | 69 µm |
| F220 | fine | 58 µm |
| Structure | Grain by volume |
|---|---|
| 0 | 62 % |
| 1 | 60 % |
| 2 | 58 % |
| 3 | 56 % |
| 4 | 54 % |
| 5 | 52 % |
| 6 | 50 % |
| 7 | 48 % |
| 8 | 46 % |
| 9 | 44 % |
| 10 | 42 % |
| 11 | 40 % |
| 12 | 38 % |
| 13 | 36 % |
| 14 | 34 % |
What do grade and structure change?
The grade is how firmly the bond holds the grains, A the softest and Z the hardest; it is not the hardness of the abrasive. The structure is how far apart the grains sit: a low number is dense, with more grain and many points cutting at once, and a high number is open, with fewer grains and more pore room to carry the chips and the coolant away.