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BANKA DRILL OPERATING MANUAL
STANDARD VERSION
BANKA drill is supplied in two versions: Size 4 (4-inch) and Size 6 (6-inch).
Size 4 is used for scout-prospecting.
Size 6 is used for the evaluation of low grade placers and/or coarse grains (gold - diamond) or coarse gravel.
Though, in easy grounds, depths of more than 40 m have been reached with the BANKA Size 4, there is a growing tendency to start drilling with Size 6 and, thereafter, to drill deeper with Size 4, the latter passing through the Size 6 casing string.
The parts for Size 4 and Size 6 are made identical as far as possible, so that a smaller number of additional parts is required when using the combination.
The casings have internal upset ends and are provided with Acme threads having a large pitch. The outside diameter of the external flush casing for Size 4 is 121 mm, and for Size 6 it is 165 mm.
The drill rods - also in standard length 1.50 m - are made of special steel and provided with robust taper threads, these being "heat-treated", as well as the pin threads of the sand bailers, tongue drills etc., to provide them with a greater wear-resistance, and less frictional resistance during unscrewing. For deep drilling with the bailer lightweight drill rods made of a special aluminium alloy in double lengths (3 m) are available.
HOW TO BORE A HOLE
(Only 4-inch size is mentioned)
First, the needed tools are: the tongue drill No.4/6-25 on which the short drill rod No.4/6-13 is screwed; the rod turner No.4/6-14 is tightened on the square drill rod and then the combination (See Fig. 1) can be rotated vertically into the ground. For easy drilling the combination should be lifted up a little occasionally, or should be withdrawn out of the bore hole for emptying the tongue drill. Rat hole drilling is usually stopped when the lower part of the sterile upper layer has been reached.
Now the borehole must be cased. (See Fig. 2). The casing shoe No.4-6, at its top, provisionally provided with the double casing wrench No.4-9 is suspended into the borehole. A standard casing No.4-6 is screwed on the casing shoe by means of a single casing wrench No.4-11 or a chain tong 4/6-43. More casings are screwed on until the cutting edge of the casing shoe touches the bottom of the drill hole.
When the casing has descended about 0.25 m. the four drillers raise the bailer as high as possible, and they keep it so until the sand within the casing has settled. The string can then be lowered until it rests on a support wrench, placed on the platform socket. After having pulled out the bailer, the operation is continued until a firm stratum is reached.
Rafal Swiecki, geological engineer:
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