Diamond Products CB744 Operator's Manual page 14

control and spins, it will immediately unplug its own cable.
ABOUT DIAMOND BITS
The diamond impregnated segments in a wet type (sintered) diamond core bit operate on a principle of
controlled erosion. The bond matrix holding the diamonds is continually worn away by abrasion with
the work piece, exposing the harder diamonds to stand proud from the bond matrix. A bit with good
diamond exposure is a sharp bit.
This erosion process causes heat and particles, which require water to cool and rinse free. Without
adequate water, the bit would overheat and be destroyed.
With too much water and not enough feed pressure, there would not be adequate erosion of the bond
matrix (the diamonds not exposed) and the bit becomes dull (diamond segments polish smooth). This
is called glazing and luckily the bit can be de-glazed (sharpened). If the bit seems to refuse to cut anymore,
you know that it is glazed.
See below: "SHARPENING A GLAZED BIT "
Never use a sharp motion or the bit will be damaged. Conversely, don't feed too gently or the diamond
segments will become glazed. Keep the bit steadily working, but don't be abusive or give the bit shock
impacts into the work surface.
If the cut is very deep, the core plug may be obstructing the flow of cooling water. In this case, stop drilling, and
chisel out the core plug before continuing.
CAUTION: If the bit gets stuck, do not try to rock it loose by turning the switch on and off. That is
hazardous and could damage the motor. Rather, unplug the machine and use a wrench on the bit
mounting to work it loose.
If embedded steel such as rebar is encountered take special care. When the steel is encountered, the water
will generally go clear and vibration will begin. Change to a lower gear if available. Reduce the feed pressure
by about 1/3 and let the bit go at its own pace, if there is too much vibration the bit will be destroyed.
Once the steel is passed, continue normally. A properly sharp bit with good diamond exposure should
be able the cut through rebar if handled well.
When the cut is finished keep the motor running until the bit is removed from the cut to avoid it getting
stuck.
CAUTION: Drilling operations are very stressful to the motor and at the end of the cut, the motor
temperature will be very hot, always run the motor at no load for a few minutes until the temperature
returns to a normal range before shutting off. Turn the water feed down to a very small amount of flow
(not off), just enough to keep the water seals from overheating when you perform this step.
Then turn off the switch and allow the coasting bit to stop before setting it down.
RESHARPENING A GLAZED BIT
If the bit becomes glazed, the ideal way to resharpen and true it up is by dressing with an appropriate alumina
oxide or silicon carbide dressing stone. Simply drill into the stick as many times as necessary to restore its
cutting performance.
If it is only slightly dull, while cutting, you may first reduce the water flow by about half until the water exiting
the kerf is really muddy.
Another method is to stop and add about 6mm (1/4") of coarse silica sand in the kerf and and drill for a few
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