page_title: Ice drilling
section_title: Anti-torque
hierarchical_section_title: Ice drilling / Drilling system components / Anti-torque
caption_attribution_description: English: Schematic of five different anti-torque devices for use in ice drilling. Redrawn from Talalay, Pavel G.; Fan, Xiaopeng; Zheng, Zhichuan; Xue, Jun; Cao, Pinlu; Zhang, Nan; Wang, Rusheng; Yu, Dahui; Yu, Chengfeng; Zhang, Yunlong; Zhang, Qi; Su, Kai; Zhan, Dongdong; Zhan, Jiewei (2014). "Anti-torque systems of electromechanical cable-suspended drills and test results". Annals of Glaciology. 55 (68): p. 208.
context_page_description: Ice drilling allows scientists studying glaciers and ice sheets to gain access to what is beneath the ice, to take measurements along the interior of the ice, and to retrieve samples. Instruments can be placed in the drilled holes to record temperature, pressure, speed, direction of movement, and for other scientific research, such as neutrino detection.
  Many different methods have been used since 1840, when the first scientific ice drilling expedition attempted to drill through the Unteraargletscher in the Alps. Two early methods were percussion, in which the ice is fractured and pulverized, and rotary drilling, a method often used in mineral exploration for rock drilling. In the 1940s, thermal drills began to be used; these drills melt the ice by heating the drill. Drills that use jets of hot water or steam to bore through ice soon followed. A growing interest in ice cores, used for palaeoclimatological research, led to ice coring drills being developed in the 1950s and 1960s, and there are now many different coring drills in use.
context_section_description: The two main requirements of an anti-torque system are that it should prevent rotation of the sonde, and it should allow easy movement of the drill up and down the borehole.  Attempts have been made to design drills with counter-rotating components so that overall torque is minimized, but these have had limited success.  Five kinds of anti-torque systems have been devised for use with cable-suspended EM drills, though not all are in current use, and some drills have used a combination of more than one design.  The first drill to require an anti-torque system was used at Camp Century by CRREL in 1966; the drill incorporated a set of hinged friction blades that swung out from the sonde when the drill motor was started.  These were found to have very weak friction against the borehole wall, and were ineffective; the drill had to be controlled carefully to prevent twisting the cable.  No other drills have attempted to use this approach.
  For the next deployment of the drill leaf springs were installed, and this has proved to be a more durable design.  These are mounted vertically, with a curve outwards so that they are easily compressed by the borehole wall, and can slide up and down with the movement of the drill.  They pass easily through any areas of irregularity in the borehole, but the edges of the springs cut into the borehole wall and prevent rotation.  Leaf springs are very simple mechanically, with the additional benefit of being easy to adjust by changing the spacing between the end points.  They can be placed anywhere on the drill that does not rotate, so they do not add length to the sonde.  The shape is usually a fourth-order parabola, since this has been determined to provide the most even loading against the borehole wall.  Leaf springs have been found to be so effective that they can prevent rotation even in heavy drills running at full power.
  Skate antitorque systems have blades attached to vertical bars which are pushed against the borehole wall; the blades dig into the wall and provide the anti-torque.  Skates can be built with springs which allow them to keep the blades pressed against the wall in an irregular borehole, and to prevent problems in narrower parts of the borehole.  Although skates are a popular design for anti-torque and have been used with success, they have difficulty preventing rotation in firn and at boundaries between layers of different densities, and can cause problems when drilling with high torque.  When they fail, they act as reamers, removing chips from the wall which can fall to the drillbit and interfere with drilling.
  In the 1970s, the Japanese Antarctic Research Expedition (JARE) group designed several drills using side-mill cutters.  These are toothed gears that are driven from the rotation of the main drill motor via 45° spiral gears; their axis of rotation is horizontal, and they are placed so that the teeth cut four vertical slots in the borehole wall.  Guide fins higher on the sonde travel in these slots and provide the antitorque.  The design was effective at preventing rotation of the sonde, but it proved to be almost impossible to realign the guide fins with the existing slots when tripping in.  Misalignment increased the chance of the drill getting stuck in the borehole; and there was also a risk of ice cuttings from the mill cutters jamming in between the drill and the borehole wall, causing the drill to get stuck.  The system was used again in a drill developed in China in the 1980s and 1990s, but the problems inherent in the design are now considered insuperable and it is no longer in use.
  The most recent anti-torque system design is the use of U-shaped blades, made of steel and fixed vertically to the sides of the sonde.  Initial implementations ran into problems with thin blades bending too easily, and thick blades providing too much resistance to vertical movement of the sonde, but the final design can generate strong resistance to torque in both firn and ice.
  Drills may be designed with more than one anti-torque system in order to take advantage of the different
caption: Five different anti-torque devices[193]
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