Core Drilling Tips:

  • For operator safety, most manufacturers recommend drilling over 67mm be done with the drill mounted in a stand.
  • Ensure there are no power lines or water pipes where you are going to drill
  • Always turn on the water (always use clean water) before turning on the motor. Otherwise the water jacket seals on the drill can overheat, which will cause them to leak.
  • For best results, apply water until the slurry looks like heavily creamed coffee. Too much water flow washes away the abrasiveslurry which is needed to keep wearing away the steel matrix and keep fresh diamonds exposed. Too little water can cause the diamond segments to overheat
  • When the slurry changes colour (usually to gray) or the drill motor speed drops, you are most probably cutting steel. Drop the motor speed down and relax pressure by about 1/3. If you don't the segments will overheat and bend inwards (occasionally outwards), and stop cutting. The barrel may also crack. Some operators reduce water after exiting the steel to redress the blade again, but don't forget to turn the water up again afterwards.
  • Similarly, if you are drilling concrete with a high strenth (or MPA), or with very hard aggregate in it, the bit may glaze up and need redressing. Do this by reducing the water by half for a few minutes, or by drilling into an abrasive material like limestone, a cinder block or similar. A bit of Ajax down the hole can also have the same effect.
  • Be aware, no two coring jobs are ever the exactly the same. Variables include (but are not limited to)– what age is the concrete, what hardness and size of stone was used, the quantity and type of chemicals added to produce harder MPA's, how much steel reinforcing rod will be drilled etc.
  • If your 127mm bit binds in limestone, United Diamond Tools have a limestone barrel specifically designed not to bind. We also sell 127mm bits with and without spirals, as well as 127mm bits for concrete and laterite.
  • When removing the bit, turn the water down and back the bit out while the drill motor is still running.
  • You can avoid stuck core barrels by:
    1. cleaning the core hole often
    2. don't try removing too large of a slug
    3.  good water pressure will help flood the sediments up from deeper holes.  Relieve the pressure on the core bit for a few minutes now and then.
    The driller's experience in deep coring is essential. The slurry from the cutting of asphalt or concrete is distinct and consistent. As soon as the core drum cuts through the bottom of the asphalt or concrete into the base, the slurry coming up to the surface will look different. Watch for the change, and then you will know you are through.
  • Need to drill dry for environmental reasons but only have a standard water-cooled core drill and bit? There have been cases of operators connecting up air to the drill instead of water, but this may not suit all applications, and air is not as efficient at cooling as water. It also may lead to damaged seals in the drill in prolonged use. But it may be ok for a small job.
  • Waterproof grease on the drill spindle thread will make bit changing easier
  • Always read your drill's operation manual before use
  • Wear correct PPE (personal protective equipment)
  • Use the drill and bits only in a safe manner as described in the operation manual
  • Be aware if  using a vacuum assembly to anchor a core drill stand to a surface, the operator may risk injury if the vacuum pump fills with slurry, or the power goes off. This can cause loss of vacuum, which can result in the drill stand breaking free and rotating round the drill.
  • If excessive vibration or 'snatching' at the core barrel is detected – stop, remove the core drill, remove the core and investigate. Remove any lose  material, pieces of cut steel rod etc. When drilling brick walls,  wall ties maybe encountered -  remove them with pliers. Failure to fix these problems may result in segment damage or loss.
  • If the drill speed is too high, the diamond segment will skip over the grinding surface. This means the core barrel bond will not wear away to expose new diamonds and the cutting edge becomes blunt or glazed over
  • On smaller diameter holes, there is a tendency for the core barrel to  wander away from the true center. This is because there is no pilot drill system to lock the barrel in the drilling position. A piece of heavy timber is sometimes used (on the outbound rotational side) to steady the bit
  • Drilling with diamonds (an abrasive technology), when compared to SDS percussive drilling, is the slowest of all cutting methods. Concrete drilling  with embedded steel can take many times longer. Have realistic expectations as to the time it requires.
  • If the drilling is slow, the blade may have glazed up. Redress the bit by reducing the water by half for a few minutes, or by drilling into an abrasive material like limestone, a cinder block or similar. A bit of Ajax down the hole can also have the same effect.
  • If your internal 1/2" thread is rusted, and won't clean up, you can still use 1/2" bits by buying a 1 1/4"UNC to 1/2" adaptor (cross over sub) from us. See them here 

Trouble Shooting:

Problem Cause Remedy
Segment bent over  Too much pressure by operator when cutting reo  Replace barrel, decrease pressure when cutting reo
Loss of Segment   Bit is too hard, causing barrel to bounce Decrease drill speed, or use softer bond
Overheating Increase water flow
Drill not held rigidly allowing vibration Hold drill firmly, or mount drill on a stand
Segments crack  Bit is too hard Decrease drill speed, or use softer bond
Drill not held rigidly Hold drill firmly, or mount drill on a stand
Barrel Cracking  Too much pressure by operator Reduce pressure
Bit is too hard Use softer bond
Belled Barrel Too much pressure by operator Reduce pressure
Bit not cutting Too little pressure by operator causes the bit to glaze up  De-glaze bit (see above) then re drill with more pressure

Core Drill Bits Speeds:

(These core drill speeds are suggested only. Always consult your drill manual for recommendations to suit your machine)

Diameter mm Drill speed
8-29mm 3,000RPM
30-45mm 1,500RPM
46-65mm 1,200RPM
66-89mm 900RPM
90-125mm 600RPM
126-200mm 450RPM
201-400mm 300RPM

Disclaimer: the information on this website is provided in good faith and believed to be reliable and accurate at this time. However, the information is provided on the basis that the reader will be solely responsible for assessing the information and its veracity and usefulness. UDT shall in no way be liable, in negligence or howsoever, for any loss sustained or incurred by anyone relying on the information, even if such information is or turns out to be wrong, incomplete, out-of-date or misleading.

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