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GENERAL
Numa button bits are designed for fast penetration and long life. Keeping the carbide
buttons sharp has a direct effect on both the penetration and the tool life.
As the bit wears flat, spots develop on the carbide buttons. These flat spots increase
stress on the buttons causing the bit to work harder, which may cause button failure. Bit
sharpening can minimize these problems.
Gauge buttons will usually show the most wear and should be used to determine the
frequency of bit sharpening. When the flats on the gauge buttons become a maximum of
1/8" (3 mm) wide it is time to resharpen. Refer to figure 7-1.
SHARPENING
The following tools are required to resharpen the bit:
• Hand grinder (20,000 r.p.m.)
• Silicon carbide wheel 1" (25 mm) diameter, 60 - 80 grit
• Bit stand
• Pencil
Place a mark on the center of the button flat. Grind the button to its original shape
leaving the mark untouched. Refer to figure 7-1. It is important to leave the center of the
flat untouched to insure concentricity.
02/09/23
SECTION VII
BUTTON BIT MAINTENANCE
1/8" MAX (3 MM)
FLAT
SIDE VIEW
SHARPEN TO
OVAL SHAPE
SIDE VIEW
Button Resharpening
Figure 7-1
Patriot
125/125HD
TOP VIEW
ORIGINAL SHAPE
Page 19
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