in fig1 the reference 10 designates an excavator chassis in its entirety . the latter supports a fault finder 14 , which is adjustable via a steering arrangement indicated in its entirety by the reference 12 . a drive carriage 16 , which operates via a drive pipe 18 on a drill pipe 20 , is displaceable in the vertical direction on the fault finder 14 . lying above the drive carriage 16 , a further drive carriage 22 , which operates on a drive rod 24 , is displaceable on the fault finder 14 . the drive rod 24 supports a drill 26 , which extends through the drill pipe 20 . provided at the lower end of the fault finder is a pipe guide head 27 , which forms a radial bearing for the drill pipe 20 . in order to produce a drill hole in the immediate vicinity of a schematically indicated building 28 , the drill 26 is rotated and forced into the soil . according to the advance of the drill 26 , the drill pipe 20 is also forced with rotation into the soil . the drill 26 constantly conveys the loosened soil upwards into the drill pipe 20 , whence it can fall downwards via openings 30 in the drive pipe 18 . once the drill 26 has reached the desired depth , it is withdrawn from the drill pipe by moving the drive carriage 22 upwards . if the pile which is to be produced is to be armoured , then an armouring is let down into the drill pipe 20 , and the drill pipe 20 is then filled with local concrete and withdrawn rotating from the drill hole . the procedure described above is repeated in such a manner that a row of adjacent local concrete piles is obtained , which can thus form a building foundation which lies in the immediate vicinity of the building 28 . the drilling machine described above can be converted from operation with a drill pipe 20 having a large diameter and a drill 26 having a large diameter , as shown in fig1 to operation with a drill pipe having a small diameter and a drill 26 having a small diameter , as illustrated in fig2 . in order to carry out this conversion simply , the drive carriages 16 and 22 each have the construction shown in fig3 and 4 , these drawings showing the drive carriages for the drill pipe , the drive carriages for the drill and the pipe guide head being similarly designed . as a modification , the upper drive carriage 22 can be constructed in such a manner that it is suitable for use together with the drill having the smallest diameter , the drive rods for the drills having larger diameters remaining the same in this case . as shown in fig3 the drive carriage 16 has a carriage base element 32 , which with lateral cheeks 34 engages around guide strips 36 , which are provided in the corners of the fault finder 14 . resting on a shoulder 38 of the carriage base element 32 is a rear end section 40 of a box frame 41 of a drive unit designated in its entirety by the numeral 42 . the latter has a downwardly hanging plate 44 , which rests against the front side of the carriage base element 32 . provided on the shoulder 38 are positioning rods 46 , which cooperate with positioning apertures 48 , which are provided in the end section 40 of the drive unit 42 . screws 50 , which cooperate with threaded bores 52 in the shoulder 38 , are used for the releasable connection of the drive unit 42 with the carriage base element 32 . further screws 54 extend through the vertical plate 44 and are screwed into the front boundary surface of the carriage base element 32 . the drive unit 42 supports two hydromotors 56 , 58 , which operate via pinions 60 , 62 on an intermediate pinion 64 . the latter meshes with a toothed rim 66 , which is constructed on the outer surface of a drive sleeve 68 , and this is mounted via a radial / axial bearing , not shown in further detail in fig3 in the front section of the drive unit 42 . in this respect , the thickness of the drive sleeve 68 and the web of the box frame 41 of the drive unit 42 enclosing the drive sleeve 68 are selected to be as small as is still acceptable in respect of the mechanical loading . in this manner , the drive unit 42 projects only slightly in the radial direction beyond the outer surface of a drill pipe 20 connected to the drive sleeve 68 , as is shown in fig1 and 2 . the drive carriage 22 for the drill is similarly constructed , with the exception that a drive disc is provided instead of the drive sleeve 68 , the drive disc comprising in its centre a polygonal ( usually square ) opening for a drill rod . the pipe guide head 27 is also constructed similar to the drive carriage 16 , but comprises a radial bearing unit , which can be removed from the carriage base element and cooperates with the outer surface of the drill pipe . if it is intended to convert the drilling machine to operation with drills having a smaller diameter and drill pipes having a smaller diameter , then the screws 50 and 54 are released and with the aid of a lifting tool schematically indicated 70 in fig1 and 2 , the drive unit 42 of the drive carriage 22 and then the drive carriage 16 are raised and placed onto the ground . the radial bearing unit of the pipe guide head 27 is then removed . a new radial bearing unit and new drive units 72 are then accommodated and again secured in reverse sequence to the carriage base elements 32 of the pipe guide head 27 , the drive carriage 16 and the drive carriage 22 . the new radial bearing unit and the new drive units have the same geometry as the replaced units with the proviso that they are designed for different diameters of drill or drill pipe . for example , if the drive sleeve 68 now has the desired smaller diameter on the drive carriage 16 , then the size of the intermediate pinion 64 is accordingly increased . since drills and drill pipes having smaller diameters can be rotated into the soil with reduced torque , it is also possible to provide smaller hydromotors 56 , 58 . it can be seen that a drilling machine as described above can be very rapidly converted for the drilling of drill holes of different diameters . in the embodiment illustrated in fig5 and 6 , parts of the drive carriage which correspond in their function to parts already explained with reference to fig3 and 4 are again provided with the same reference numerals . these parts are not described again in detail in the following . in this case , an upper plate of the box frame 41 of the drive unit 42 has a rectangular opening 74 . the edges of the opening 74 extending towards the free ends of the drive unit simultaneously act as guide rails for guide grooves 76 , which are provided in lateral surfaces of a motor plate 78 . the motor plate 78 supports the hydromotors 56 , 58 as well as the intermediate pinion 64 . in order to move the motor plate 78 in a horizontal direction perpendicular to the fault finder , two hydraulic cylinders 80 are used , which are supported against the rear end section 40 of the housing 41 of the drive unit 42 . the intermediate pinion 64 has a bearing collar 82 , which lies beneath the toothed rim of the intermediate pinion , projects radially beyond the pinion toothed rim 66 and runs axially beneath the pinions 60 , 62 . the bearing collar 82 has a trapezoidal cross section . a bearing groove 84 , which has a cross section matching the bearing collar 82 , is cut into the drive sleeve 68 beneath the toothed rim 66 . in the case of the free end of the drive unit 72 , bearing rollers 86 , 88 having small diameters are mounted , whose contour also matches the bearing groove 84 . the drive sleeve 68 is thus mounted by the intermediate pinion 64 with its bearing collar 82 and the bearing rollers 86 , 88 . by moving the motor plate 78 in the direction of the fault finder 14 , the bearing collar 82 can be moved away from the drive sleeve 68 to such an extent that the latter is released from the bearing rollers 86 , 88 and can be removed from the box frame 41 . a drive sleeve 68 having a smaller diameter can then be inserted and the motor plate 78 can be moved away from the fault finder to such an extent that the bearing sleeve 68 simultaneously engages again with the bearing collar 82 and the bearing rollers 86 and 88 . a correct engagement between the toothed rim of the intermediate pinion 64 and the toothed rum 66 of the drive sleeve 68 is then simultaneously produced , since all drive sleeves which are to be used together with the drive carriage comprise toothed rims consisting of teeth having the same shape . the engagement relationships between the intermediate pinion 64 and the bearing rollers 86 , 88 on the one hand and the drive sleeve 68 on the other hand can be clearly seen from the angled sectional view of fig7 . the further modified embodiment according to fig8 differs from that according to fig7 only in that two intermediate pinions 64 a and 64 b are used instead of a single intermediate pinion 64 , the two intermediate pinions being arranged symmetrical to the vertical centre plane of the drive carriage 16 in fig8 . in the embodiment according to fig9 the bearing rollers 86 , 88 are supported by a bearing plate 90 , which with guide shoes 92 engages over the lateral edges of the box frame 41 . the bearing plate 90 is adjustable and lockable by hydraulic cylinders 80 . also in this manner , the drive carriages 16 can bear and drive drill pipes having different diameters . it is , of course , also possible to use sliding bearing elements instead of the bearing rollers 86 , 88 shown in fig5 to 9 , the sliding bearing elements cooperating with the bearing groove 84 and only extending over a small circumferential region , so that they can cooperate equally well with circular bearing grooves of different diameters . in the case of the drive carriage according to fig1 , the hydromotors 56 , 58 are fitted to support plates 94 , 96 , which are fitted to the carriage base element 32 independent of the housing 41 and are accommodated in recesses 98 , 100 in the housing 41 . the adaptation of the drive carriage to the respective drill pipe diameter is effected merely by exchanging the bearing and gearing unit , which is formed by the components 41 , 64 , 66 , 68 . in this manner , the unit which is to be replaced is cheaper , and the connections to the hydromotors do not need to be released in order to convert the drill pipe diameter .