ODDS’N’SODS — The detachable drill bit

I well remember the good old days when the “integral” drill rod was employed in mining. After use, each rod was carefully carted to the blacksmith’s shop where the bit was thrust into glowing coals to be resharpened or reshaped on the ram.

Each drill hole was started with a shore “starter” rod, and there followed an 18-inch increase in the length of each followup drill rod in the hole, with a slight reduction in bit diameter. At the end of the shift, a minimum of 10-12 sets of dull drill rods had to be removed from each workplace. At the Sheep Creek mine in Salmo, B.C., the “bull” quartz vein was so tough that it required the use of four bits to “collar” a hole. In those days, the mine needed servicemen — or “nippers,” led by the “King Nipper” — to handle the volume of drill rods taken into the mine each day.

Then came a change: the detachable bit appeared. This was a “one-pass” steel bit threaded on the end of the drill rod (or wedged on the tip, as the case might be). Brand names such as Craig and Liddicoat pass through my mind. They were not foolproof — some broke and were lost in the hole, and the mines charged the bits against the “bonus” system. However, the introduction of these bits greatly reduced the weight of steel transferred each day into the mine.

Copco came out next with the tungsten-carbide bit, set up on an integral rod. It was a major change because, with a bit sharpener in the workplace, the same rod and bit could be used again and again without any transport. Meanwhile, the speed of drilling increased with the use of the hard, tungsten-tipped steel. Rounds were drilled off in short order. Then came yet another innovation — a detachable tungsten-carbide bit on a much-strengthened drill rod.

A mere dozen bits, of varying diameter, were taken by the miner on a wire sling to his workplace and were sufficient to complete the day’s drilling. They were returned, at shift’s end, to the shop for resharpening. All bits are subject to excessive wear, owing to the abrasiveness of the rock. Consequently, great skill is required, on the part of the miner, as regards the use of water to remove the sludge, correct alignment and maintain steady pressure on the face of the bit while drilling.

As such practices illustrate, the detachable bit changed the drilling process for all time.

— S.J. Hunter, a retired mining engineer and regular contributor, resides in Vancouver, B.C.