9
WARNING: Take care that the bit does not come crashing down when the height adjustor is
loosened.
6. Diamond Core Drilling
WARNING: When coring through a oor, the core will fall down. Take precautions to avoid
injury or damage below.
NOTE: When cutting with a new bit for the rst time, use less than normal feed pressure for
a time until it breaks-in.
a. With all connections ready and secure, place the machine in the exact position desired.
With the bit raised or removed, hold the centering aid pointer in the fully open position
against the spring tension. It will indicate the exact center of the cut. Double check
position, then turn on the vacuum pump and push down on the base to allow it to build
vacuum. Allow it to achieve at least 10psi (0.7 bar) or more of vacuum.
b. Turn the machine on, open the water valve slightly and very gently begin the cut.
Use very light feed pressure to prevent the bit from wandering until the bit is fully
penetrated into the cut.
c. Make adjustments to the water feed as needed. The water leaving the cut should
have a solid color. If the exiting water is clear, then reduce the water .
If the exiting water is thick and muddy, then increase the water. It’s very important
that the water has enough pressure to ush cutting debris out of the cut.
d. Once in the cut, use steady feed pressure for about 30 seconds, then back off the bit
for about 10 seconds to allow cutting debris to escape the kerf (cutting area) and for the
bit to cool. Then repeat this cycle until nished.
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. Make the bit work, but don’t be abusive
or give the bit shock impacts into the work.
If the cut is very deep, the core plug may be obstructing the ow of cooling water. In this case,
stop drilling, and chisel out the core plug before continuing.
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. Feed very gently
and let the bit go at its own pace, if there 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.
