NUTOOL BT1550 - Page 23

23
GB
render them useless. Soft wheels give themselves up while
grinding.
When grinding, only a small amount of material is removed,
and the wheel releases grains a little at a time, presenting new
cutting edges. This releasing activity helps to keep the tool from
heating up and gives a finer grinding result.
Table 2 shows wheel hardness and uses.
TABLE 2
WHEEL HARDNESS
(GRADE)
USES FOR DESIGNATED HARDNESS
DESCRIPTION OF HARDNESS
A B C D
Not used very often
Very soft
E F G H I J K L
Use these soft wheels to sharpen high-speed-steel tools,
such as router bits, drills, and tool bits.
Soft to medium
M
N O P Q R S T
Use these wheels for rough grinding on soft materials
Medium to hard
U
This hard grade is used for dressing sticks to dress grinding
wheels.
Hard
V W X Y Z
Not used very often
Very Hard
The following table 3 should help you to select the correct
grinding wheel for the job.
New bench grinders are supplied with grey wheels. All
other types of grinding wheel are available from your
tool stockist.
TABLE 3
TYPE OF TOOL
TOOL MATERIAL
RECOMMENDED WHEEL TYPE
Drill bits
High-speed steel
Aluminium oxide (grey)
Spade boring bits.
High-speed steel
Aluminium oxide (grey)
Masonry drill bits
Cutting edge is carbide
Silicon carbide (green)
Lathe tool bits
High-speed steel
Soft aluminium oxide (Pink or white)
Chisels
High-speed steel
Soft aluminium oxide (Pink or white)
Router bits
High-speed steel
Soft aluminium oxide (Pink or white)
High-speed steel carbide tipped
Cutting edge is carbide
Silicon carbide (green)
Rotary lawnmower blades
Non heat-treated steel
Aluminium oxide (grey)
Scissors & snips
Hard steel (but not file hard)
Aluminium oxide (Pink or white)