Basic Drilling Hints

  1. Do not start rotation with the drill bit on the bottom of the hole. Always start flushing, then rotation, and then the feed slowly until the drill bitstarts to take weight on the bottom of the hole. Gradually increase the RPM and the weight on the drill bit until an acceptable rate of penetration has been achieved. Do not over feed as this will lead to the diamonds polishing and excessive weight having to be applied.
  2. BEWARE VIBRATION. Vibration destroys the diamonds and hence will destroy the drill bit.
  3. Ensure that there is adequate flushing to lubricate the drill bit and rod string and effectively flush the cuttings from the hole. NOTE variations in the flush pump pressure indicate leaking or cracked rods. IMMEDIATELY cease drilling and check the rod string.
  4. At the end of the feed stroke always allow the rod string to rotate long enough to reduce the compression on the rod string.

 

Reading the Drill Bit:

  1. The ideal drill bit face wear should be reasonably flat with well developed comet tails behind the diamonds and a low degree of diamond "pull-out".
  2. CONCAVE wear on the face indicates over-feeding. In this case either reduce the weight on the drill bit or increase the RPM.
  3. CONVEX wear pattern indicates under-feeding. In this case either increase the weight on the drill bit or reduce the RPM.
  4. Sheared or broken diamond indicates excessive vibration. Check rod lubricant and adjust RPM until vibration disappears.
  5. Highly exposed diamonds indicate that a tougher bond should be used, or alternatively a higher RPM can be used. A good rule of thumb is that  A) the higher the RPM - the harder the bond reacts and B) the lower the RPM the softer the bond reacts.