Operating principles: Table Tool drilling is usually recognised as a process of advancing the hole by:
1. breaking or stirring the formation,
2. mixing the resulting cuttings roto a slurry with
water in the bottom of the hole,
3. removing the cuttings by bailing.
Other table tool methods include the robe sampling or "shell" method, which advances the hole by driving a tube into the formation and removing the robe with the retained solid cylinder cut from the formation. This method may:
* drive the sample tube by repeated blows using a reciprocating or "spudding" action,
* work the sample tube down using a repeated raising and dropping action,
* impact the sample tube into the bottom using one long drop.
The last two methods are frequently used on light table machines which are not equipped with a powered reciprocating action.
Another similar system is the Banka drill, developed in Indonesia in the 1880s to drill and sample alluvial deposits. In this system, the casing is driven or rotated down and then the contents are bailed out, leaving a 5-10 cm (2-4 inch) plug in the bottom.
The semi mechanical Bank a is basically a table tool rig with a single winch supplying the percussive, chopping, and bailing actions. The Banka driller manually performs the percussive snapping provided by the spudding arm on a fu 11-mechanical table tool dg. The casing is hammered down by free-fall action with the bailer attathed as a guide. It is then bailed with the drive hammer unclamped. A sinker bar provides chopping and hammering weight and keeps the hole aligned. The swivel allows the tool string to spin and turn.
Table tool percussion drilling: The early table tool reciprocating action was achieved using a "walking beam".
Today the required reciprocating motion is imparted by a "spudder". Usually a spudding arm working on the bight of the drilling table (the bend around the spudding arm pulleys), lifts the tool string quickly and allows it to drop freely. The spudding arm must tighten the table to "catch" the drill string just before it reathes the bottom, so that impact with the bottom is achieved with the table at "full stretch ".