This invention relates to a drilling apparatus according to patent claim 1, the drilling equipment of which can be de¬ tached from and refixed to the drill bit when the apparatus is drilling.

Previously known from the Finnish patent No. 86571 is an appa¬ ratus drilling with a rotating and hammering drill bit, where the hammering machine is behind the drill bit and which has between the protective tube and the drill bit holder a joint, by means of which the drill bit can pull the protective tube forward. In this construction the drill bit is fixed direct or by means of a bit holder to the spindle of the hammering machine with a taper thread. The thread joint is screwed most tightly in order not to get open while drilling. The thread may get open if the bit hits soft ground without hardly any resistance. In drilling state, the thread joint can neither be opened nor tightened since the drill bit may then rotate free¬ ly. Yet, it is possible to rotate the hammering machine in both directions from the tunnel or bore orifice, for instance by means of the drilling apparatus center tube but the rotat¬ ion of the drill bit cannot be stopped simultaneously.

If the hammering machine does not work or the bore comes to a dead end or, if for some reason, the hammering machine and the transportating thread or the transportating tube should be taken off during drilling, it cannot be done with previous constructions in using a single drill bit. It has been pos¬ sible to open the joint between hammering machine and drill bit only with tools and whith the drilling unit outside the bore. Furthermore, several drilling aggregates are known, where the drill bit is solely controlled by the hammering machine, i.e. the suspension of bit to protective tube is lacking. In such constructions the drill bit may change direction or escape forward in soft soil, if it, for some reason, has got off its anchorage in the hammering machine. It

is then impossible to get the drill bit refixed to the hammering machine.

With a construction according to this invention these problems are eliminated and the invention is characterized in what is presented in the patent claims.

The advantages of the invention are that even in a drilling unit, where the drill bit cannot be pulled out from the bore, at least the most significant parts, for instance the hammer¬ ing machine and the transportating equipment, can be taken out from the bore and also be put back if drilling is continued. In advance, the drill bit can be made less valuable so that in certain cases, for instance when the drill bit arrives at a dead end, the bit can be left, intentionaly, in the bore. On the other hand, the drill bit can be made long-lasting since by means of the inventional con-struction it possible to carry out service in the hammering machine even during drilling by pulling it out from the bore and, accordingly, the probability of successfull drillings grows and more often one can drill through to final destinations. The steering joint between drill bit and protective tube keeps the drill bit constantly in place in the bore when the hammering machine is pulled out.

In the following the invention is disclosed with reference to the enclosed drawing, where

Fig. 1 is a side section of the drilling apparatus

Fig. 2 is a joint between hammering machine and drill bit

Fig. 3 is the joint viewed from the end

Figure 1 shows the drilling apparatus comprising a hammering machine 1, outside of it a protective tube 2, which will re¬ main in the bore, an extendable transportation tube 3 behind the hammering tool, and a hammering and rotating drill bit 4. The drill bit is furnished with working buttons 5. The outer drill bit shell has a groove 12 matching with ring 8 in the edge of protective tube 2 to restrict axial motion between

drill bit and protective tube. Through drill bit 2 runs a channel 6 for conveyance of compressed air from hammering machine to the front of the drill bit, from where it conveys drill waste further backwards through chan-nel 7. By means of its hammering surface the hammering machine piston 9 is in direct contact with drill bit 2, against which the strokes are transmitted. In addition, the hammering machined is pushed from the rear by suitable force over the transportation tube line in order to retain contact in the hammering surface at least at the moment of stroke. As per figure 1 the transport¬ ation tube 3 and hammering machine 1 can be pulled out from bore while drill bit 4 remains suspended in protective tube 2. The construction in figure 1 is a simple version of the in¬ vention. Anyhow, for securer operation, the drill bit and the hammering machine joint must be furnished with locking or steering means to secure that the drill bit and hammering machine piston retain their concentricity while rotating.

Figure 2 shows a version of locking means between drill bit and hammering machine. In the hammering machine piston 9 there are pins 10 or similar projecting parts, which by means of a tiny rotative motion match behind corner pieces 11 in the counter-part, i.e. the drill bit. Fig. 3 shows the same ver¬ sion viewed from the end. Thanks to low locking force, smaller than the resistance of rotation, such a joint opens and locks also in the bore.

The joint between drill bit and hammering machine can be made by a number of easily detachable methods, the common feature of which is that, for transmission of stroke to the drill bit, a hammering surface is produced between hammering machine pis¬ ton or spindle and the drill bit has steering surfaces or ele¬ ments to ensure that the piston remains on the counter-face during rotation and dril-ling and the spindle or piston of the hammering machine is steered to the counter-face, when the hammering machine is being refitted into the bore and approaching the drill bit.

The cheap simple single drill bit can be left in the bore when the other equipment is pulled out from it. Thereby, the drill bit is made as a relatively thin disc supported by a spindle, which is pulled out with the hammering machine. This arrange¬ ment often comes up on drilling downward, whereby they end at a certain depth.