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BANKA DRILL OPERATING MANUAL
DRILLING METHOD
Briefly, the drilling method is as follows:
a. Place a casing, fitted with a casing shoe, in a shallow hole in the ground, fit the platform for the four drillers on top of the casing, which is then rotated slowly by another two to four men. In this way the casing is sunk down by a combination of the weight of the platform and the four drillers, and the reduction of friction resulting from the rotation of the casing.
b. The cylindrical column of alluvial material, cut off by the casing shoe, is taken out with a bailer, which is screwed on the drill rods.
c. The casing string should sink more or less simultaneously with emptying the borehole. For the investigation of alluvial ore deposits no drilling should be done under the casing shoe. The casing should be pushed ahead at least 10 to 25 cm and in this way a representative sample is obtained by the "BANKA" drill, which - with respect to quantity and quality - cannot be obtained by any other simple drilling method.
The platform socket No. 4/6-3 is screwed on the casing string then the platform No. 4/6-2 is mounted thereon. Then, the whole is rotated by hand in a clockwise direction to tighten all thread connections and to ensure that the casing string is lowered into the borehole as far as possible. Now, a pole is put through each of the eye links of the platform socket and the drilling aids can rotate the casing string.
Meanwhile the drilling tools are lowered into the borehole by the drillers - usually 4 men - standing on the platform.
First, the sand bailer No. 4-47 is picked up with catch fork No.4/6-18, lowered into the casing, supported on the top of the platform socket.
Then the short steel drill rod No.4/6-13 is screwed to the sand bailer by means of rod lifter No. 4/6-17 and then the standard steel drill rods No.4/6-15, until the tools have come to depth.
One or two rod turners No. 4/6-14 are fixed crosswise at the desired height on the drill rod above the platform, so that the drillers can fill the bailer with short strokes. A slight turn to the right is given with each stroke. Always keep enough water in the hole; otherwise the valves of the bailers will not set properly. How much the cutting edge of the drilling tools falls behind with respect to the bottom of the casing shoe (distance "X" fig. 3) can, thanks to the use of uniform lengths for casing and drill rods, be ascertained easily according to the rule:
"When the cutting edge of the tool is level with the cutting edge of the casing shoe, the connection of the last two drill rods is just level with the top of the platform socket."
Rafal Swiecki, geological engineer:
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