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Core drilling made simple
There are a lot of factors that affect core drilling.
Knowing what these factors are can allow you take action
to minimize your cost while maximizing your efficiency.
Core Drilling is mostly about power & speed
The smaller the hole, the faster the required RPMs As the diameter of the hole increases the need for more horsepower also increases. If you're looking to purchase a new motor or rig to core drill, the most important question is what diameter hole(s) are required.
Match the motor to the Core Bit.
Use the Bit Size to find the motor

How to get started Core Drilling

  1. Determine the size of hole(s) required.
  2. Use the above chart "Core Drill Diameter RPMs & HorsePower" and write down the "Min RPM" "Best RPM" and "Max RPM" for each size hole you anticipate drilling.
    1. These RPM numbers represent the capabilities needed for the core drill motor you will need to use.
      • You may see RPM's represented as "Loaded" or as "No-Load" RPMs. Generally "Loaded RPMs represent approximately 60% of the "No-Load" number. The RPM numbers required for each hole need to be "Loaded RPMs" as drilling requires "loading" the motor with force in order to actually drill the hole.
    2. Are any of the holes you will be drilling larger than 3" in diameter? 3" diameter holes and smaller may be drilled using a Hand-Held Core Drill Motor. Larger holes require a Core Drill Rig setup in order to ensure drilling accuracy. Attempting to drill holes larger than 3" in diameter with a hand-held motor increases the odds that the drilled hole will be "off-center" and inaccurate. In other words you will have a very difficult time fitting a 4" pipe into a 4" hole drilled without a core drill rig. When precision drilling is required, always use a core drill rig.
    3. With the above in mind, select the best core drill motor, or core drill rig assembly with motor for your budget and job needs.
  3. Finding the best core drill bit for the job.
    1. All wet cutting core bits require water for cooling and performance.
    2. Know what you're cutting. Select a core bit most suited to the material being cut. When you click on the core bit size you're looking for you'll see the core bits shown by what they're cutting. General Purpose Bits, Hard Material / Reinforced Material, and Soft Abraisive Materials (Asphalt).
    3. Core Bits can also be special ordered. Special orders can modify production bonds to either harden the bond for more resistence to soft abrasive materials prolonging a bit's life, or softening the bond to more aggressively attack harder materials accelerating cutting speed.

How Diamond Core Bits Work

Diamond blades don't cut they grind! The exposed diamond crystals do the grinding work. The metal matrix or bond holds the diamonds in place. Trailing behind each exposed diamond is a "bond tail" which helps to support the diamond. As the blade rotates through the material the exposed surface diamonds grind.

After several thousand passes through the material being cut the exposed diamonds begin to crack and fracture. The matrix holding the diamond also begins to wear away.


Eventually the diamond completely breaks up and it's fragments are swept away with the material that it is grinding.

As the old diamonds are worn down they are replaced by new ones and the process continues until the blade is worn out.
Factors that greatly effect core drilling
Speed
(RPM) - If the speed is too high the bit will polish. If the speed is too low the job will take too long. You will know if the bit is "Polished" or "Glazed" when it stops cutting, you have segments left, and you don't see exposed diamonds. To open up the diamonds try drilling in soft abrasive material like a cinder block. Be careful to not drill very much as you will be wasting diamonds.
Power
Necessary to maintain the proper cutting speed. Efficient cutting means keeping the bit at the right speed.
Water
Not too little and not too much. The right amount removes slurry and keeps the cut clean. Slurry water should look like "Coffee with cream"
Aggregate
You can't see it until you're done, but a good driller can feel the right speed and pressure to cut varying types of aggregate.
Steel
Slows down the cutting process. Maintaining drill motor speed is important. Don't push the bit too hard. Maintain even speed with even pressure.
Bond Specs
Too hard and it takes too long. Too soft and it costs too much money. Remember Hard bond for cutting soft abrasive materials, soft bond for cutting hard materials. "Hard on hard" won't cut, and "soft on soft" won't last.
Proper Alignment
Necessary for good bit life. This means the rig must be properly anchored. A rig can be anchored with concrete anchors, vacuum or a post jack. Standing on the rig is DANGEROUS and not acceptable
Core Rig Maintenance
Performance, speed and bit life will mean little if your rig has bad shims, bearing and hold down devices.
Wet Core Bits by Size