[0040] The motor housing end cover 18 of the rear unit 2 can be joined with the motor housing 17 by screws that extend with clearance through holes in the motor housing end cover 18 and that are screwed in threaded holes in the motor housing. Correspondingly, the gear housing end cover 21 can be joined with the gear box housing 20 in order to form the integral front unit 4, with screws extending with clearance through holes in the gear housing end cover 21 and being screwed to the gear box housing.

 [0041] Referring to FIGS. 3 and 4, the gear housing end cover 21 is accordingly joined with the gear box housing 20 by a number of not shown screws, in order to form the front unit 4. A number of first screw holes for these screw joints have been denoted 24. Correspondingly, the motor housing end cover 18 can be joined with the motor housing 17 by screw joint. A number of second holes, through which screws can extend with clearance to join the motor housing end cover 18 with the motor housing 17, have in FIGS. 3 and 4 been denoted 25. The thus assembled front unit 4, comprising the gear box housing 20 and the gear housing end cover 21, can by additional screws be joined with the assembled rear unit 2 that comprises the motor housing 17 and the motor housing end cover. Accordingly, a pair of third mounting screws extends with clearance through third screw holes 26 in protrusions 27 on the upper side of the motor housing end cover 21 and through fourth screw holes 28 in the upper part of the gear housing end cover 21. The said fourth screw holes 28 extend through protrusions 29 on the gear housing end cover 21, which protrusions 29 abut against the protrusions 27 on the motor housing end cover 18, when the machine is assembled, FIG. 6. Accordingly, said third mounting screws for the joining of the rear unit 2 with the front unit 4 extend from the back, first through the third clearance screw holes 26 in the previously assembled motor housing end cover 18, and then through the screw holes 28 in the also previously assembled gear housing end cover 21 and into threaded holes in the gear box housing 20. A couple of screwdriver recesses 30 are provided on the upper side of the motor housing 17. On the underside, a couple of fourth mounting screws 31, FIG. 2, extend with clearance through holes in the gear box housing 20, and then with clearance through fifth holes 34 in the gear housing end cover 21 and sixth holes 35 in the motor housing end cover 18, in order finally to be screwed into threaded screw holes 36 in the motor housing 17, FIG. 2.

 In the mounted assembly, the gear housing end cover 21 abuts edge to edge against circumferential rear edge of the gear box housing 20, such that the outside of the gear box housing 20 passes smoothly to the outside of the gear housing end cover 21, FIGS. 3 and 4. The front circumferential edge of the motor housing end cover 18 abuts against a portion that protrudes backwards below the protrusions 29. The surfaces that face the motor housing end cover 18, against which the motor housing end cover 18 abuts by planar edge portions 41a, 41b, have been denoted 42a and 42b, respectively. The surfaces 42a and 42b and recessed portions 42 that are positioned them between, together form the edge of a dish-shaped depression 43 in the gear housing end cover 21, which accordingly has a concave side that faces the motor housing end cover 18. The depression 43 lowers itself stepwise down from the edge-forming surfaces 42a, 42b, 42c. First, there is a cylindrical or possibly slightly conical first wall portion 44, followed in order by an annular first shelf 45, a second cylindrical wall portion 46 that is considerably much longer than the first wall portion 44, as well as a bottom 47 that is planar or slightly sloping towards the centre. The circumference of the bottom is oval with its longitudinal axis coinciding with the vertical plane that forms the plane of the section in FIG. 6.

 [0043] In the bottom 47 there is a countersinking 49 that also is stepped as well as a cylindrical sleeve-shaped projection 50. The countersinking 49 exhibits, as seen from the bottom 47, a third cylindrical or slightly conical wall portion 51, a planar or slightly conical annular shelf 52 and, at the very bottom, a cylindrical or slightly conical through hole 53. The rearmost section 57 of the drilling shaft 8 extends through a cylindrical hole 55 in the gear housing end cover 21, FIGS. 3-5, coaxially with the cylindrical sleeve-shaped projection 50 and backwards to level with the upper edge of the projection 50, such that an annular groove 54, FIG. 6, with cylindrical walls is formed between the inside of the projection 50 and the outside of the drilling shaft section 57. This annular groove 54 has been marked by dashed lines in FIG. 6. The gear housing end cover 21 exhibits, on its opposed convex side, a sturdily dimensioned projection 58 that has a bore in the form of the hole 55, thus prolonging the hole 55. Hereby, the projection 58 forms an annular seat 60 for a needle bearing 59 for the drilling shaft portion 57. Similar to the annular groove 54, the annular seat 60 has been marked by dashed lines in FIG. 6. 钻孔机英文文献和中文翻译(4):http://www.youerw.com/fanyi/lunwen_56212.html