Image Number 2 for United States Patent #4889194.
A device for drilling deep holes in the ground has at least two axial drill bits and an equal number of plates each having three shafts axially interconnecting the plates. Two of the shafts are rigidly attached to both plates and the third shaft is pivotably attached to both plates. The two rigid shafts are separable from the upper plate by pulling a locking pin separating a telescopic head of each shaft from the plate. At the separation, the shafts are telescopically shortened by springs and the drilling liquid is automatically shut off to the worn-out drill bit and opened to the new drill bit. The remaining third shaft eccentrically interconnects the plates, whereby the lower worn-out drill bit, at rotation, wears a semicircular evacuation pocket in the wall of the hole. The third shaft is successively pivoted outwards until it forms an angle of e.g. 80.degree. with the axis of the hole. An axle pin having rectangular cross-section retains the upper end of the third shaft via a sleeve with a slit. The slit has such a dimension that the narrowest cross-section of the axle pin can pass through the slit at said angle for releasing the third shaft from the second plate for placing the worn-out drill bit with three legs and plate in the evacuation pocket thus formed.