Patent Publication Number: US-3878905-A

Title: Drill, especially rock drill

Description:
Umted States Patent 1191 1111 3,878,905  
 Schaumann Apr. 22, 1975 DRILL, ESPECIALLY ROCK DRILL 2.575.239 11/1951 Stephens 175/383 2,888,247 5/1959 H l d l75/410 X [75] Schwmam&#39;t wemgamm 2.902.260 9/1959 T1155: 175/394 Germany 3,052,310 9/1962 Kinzbach 175/410 3.089.552 5/1963 Black et al 175/410 X [73] Ass&#39;gnee&#39; g gz zz 3.330.601 7/1967 Proctor .175/413 x 23 sverkzeugfabfic 3,672,455 6/1972 Foster 175/418 x Ravensburgh Ravensburg Germany 715.145 9/1931 France 175/394 22 F I I [led Apr 1973 Primary E.\&#39;aminerErnest R. Purser [21] Appl. No.: 349,611 Assistant Examiner-Richard E. Favreau Attorney, Agent, or FirmWalter Becker [30] Foreign Application Priority Data Apr. 7. 1972 Germany 2216760 I&#39;7] ABSTRACT A drlll. especially a masonry and rock drlll, 1n Wl&#39;llCh a [52] CL 175/383; 175395. 75/415. fluted shank has a transverse: slot in the working end 299/92 and a hard cutting plate seated in the slot and retained 511 1m. 01. E2lc 13/08 herein by a Pin mm/ably mounted in the shank- The 158 Field of Search 175/394, 395, 410, 383, cutting Plate may be indexable in to expose 175mm 413 414 415, 313; 299/92 respective regions thereof for cutting operations. The  
  cutting plate engages the bottom of the slot and is sup- [56] Reerences Cited ported thereby. The engagement of the cutting plate UNITED STATES PATENTS by the bottom and side walls of the slot and by the pin holds the cutting plate against displacement in the 395,034 12/1888 Coffin 175/401 X slot. 994.668 6/1911 Childs 175/383 2.205.238 6/1940 Burt 175/410 X 36 Claims, 13 Drawing Figures DRILL, ESPECIALLY ROCK DRILL The present invention relates to a drill, especially rock drill, with a drill shank which has its circumferential surface provided with at least one groove for the drilling dust and which has its drill head provided with a transverse slot having inserted thereinto a plateshaped cutting member which is located in an axial plane of the drill shank and is made of hard metal.  
  It is an object of the present invention so to design a drill of the mentioned type that, when the drill becomes dull, it will be possible in a short time to provide the same with a new sharp blade or cutting edge while the design is such that the cutting member will be safely held in the drill head.  
  This object and other objects and advantages of the invention will appear more clearly from the following specification in connection with the accompanying drawings, in which:  
  FIG. 1 represents a view showing a cutout portion of a drill according to the invention.  
  FIG. 2 illustrates a section taken along the line II II of FIG. 1.  
  FIG. 3 is a section taken along the line III III of FIG. 2.  
 FIG. 4 shows a top view of the drill of FIG. 1.  
  FIG. 5 represents a further embodiment ofa drill according to the invention and is illustrates similar to FIG. 4.  
  FIG. 6 is a view of still another embodiment of the cutting member in a drill according to the invention.  
  FIG. 7 shows the cutting member of FIG. 6 as seen in the direction of the arrow A of FIG. 6.  
  FIGS. 8-l0 show still another embodiment of a drill according to the invention and illustrated in a manner corresponding to that of FIGS. 1-3.  
  FIG. ll illustrates another embodiment of a drill according to the invention in an illustration similar to that of FIG. 9.  
  FIG. 12 is a section taken along the line XII-XII of FIG. ll.  
  FIG. I3 shows a further embodiment of a drill according to the invention in an illustrated corresponding to that of FIG. 3.  
  The drill according to the present invention which has its drill shank provided with at least one groove for the drilling dust and has its drill head provided with a transverse slot in which is inserted a plate-shaped cutting member of hard metal or the like is characterized primarily in that the cutting member which is exchangeably inserted into the transverse slot is by means of a detachable holding element secured relative to the drill shank, the holding member being formed by a bolt which is located about at a right angle with regard to the drill axis and is arranged within the enveloping surface of the drill. This bolt engages recesses in the drill shank and in the cutting member.  
  In this way the cutting member may at any desired time quickly be exchanged while the arrangement of the bolt in conformity with the invention will assure a safe holding of the cutting member.  
  According to a simple embodiment of the drill according to the invention, the bolt is located at a right angle with regard to the cutting member while engaging the cutting member only over a short portion of its length. When the bolt is arranged parallel to the plane of the cutting member, the bolt will be able for all practical purposes over the entire width of the cutting member to engage the cutting member and the drill shank. It is furthermore expedient to have the bolt located approximately symmetrically with regard to the cutting member. In order to realize particularly favorable strength conditions, the axis of the bolt intersects with the axis of the drill.  
  For further simplifying the construction of the drill, the bolt engages a recess forming a passage, especially a bore, provided in the cutting plate and/or the drill shank. However, it is also possible that the bolt engages a groove, especially a groove of a cutting plate and/or of the drill shank while the groove corresponds in cross section to the bolt so that the cross section of the cutting blade or of the drill shank need not be completely perforated for receiving the bolt. According to an embodiment which is simple to handle, the groove is provided on a lateral surface of the cutting member and/or the cross sectional slot of the drill shank. The groove in the cutting plate may extend over the entire width of the cutting plate so that the bolt can easily be introduced and pulled out again. For realizing a safe guiding of the bolt, at least one groove, especially the groove in the drill shank, is undercut. &#39;The groove in the cutting member and the groove in the drill shank form a passage bore for the bolt so that the latter will be safely held and a high strength connection will be assured between the cutting member and the drill shank.  
  In order to be sure that in spite of the relatively large cross section of the bolt also very thin cutting plates may be employed, the groove in the cutting member has a flatter depth than the groove in the drill shank, especially a depth which is approximately one third of the depth of the groove in the drill shank.  
  A particularly advantageous design of the invention consists in that the bolt is offset relative to the central axis of the recess in the cutting member toward the bottom of the transverse slot so that the bolt when being introduced will be preloaded in a direction transverse to the longitudinal direction of the bolt in such a way that with this preload it will press the cutting member against the bottom of the transverse slot and thus will assure a completely play-free hold of the cutting member. This may also be realized by forming one recess, especially the recess in the cutting member for the bolt, by an elastic spring member inserted into a correspondingly larger receiving opening. The spring member is formed in a simple manner by a spring sleeve and preferably may be of rubberelastic character.  
  It is furthermore possible as bolts to provide screw bolts. However, a particularly simple construction and a very simple handling will be obtained when the bolt is formed by a press pin, in particular a spiral clamping pm.  
  For purposes of resting and avoiding relative movements between the cutting plate and the drill, the cutting member has that edge thereof which faces away from the cutting edge arranged in engagement with the bottom of the transverse slot, preferably approximately over the entire diameter of the drill shank.  
  A further increase in the strength of the drill can be realized by providing the transverse slot and/or the bolt symmetrically with regard to the end sections of the drilling dust grooves which end sections are provided on the drill head and in particular are approximately axis-parallel with regard to the drill. In this way also a more favorable drilling dust removal directly from the drill tip will be assured. This arrangement will be further improved when the end sections of the drilling dust grooves are located on both sides of the transverse slot and/or of the bolt at a distance from the bolt.  
  A very favorable removal of drilling dust at high drill strength, especially within the region of the drill tip, is obtained when the end sections of the drilling dust grooves merge in the direction toward the center of the drill shank and in axial spacing from the bottom of the transverse slot with spiral drilling dust grooves. It is also within the framework of the present invention to have the drill at the circumference thereof provided with merely one or two lateral axis-parallel flat grooves or the like for the removal of the drilling dust. For increasing the cross section of the drill head, the width of the end sections is less than the width of the spiral-shaped drilling dust grooves. According to the invention, two or four drilling dust grooves may be provided so that also a larger quantity of obtained drilling dust can quickly be withdrawn.  
  For realizing a high drilling output, the respective cutting edge of the preferably multi-edged cutting member. which may have one or more cutting edges, is formed by two cutting edges forming an acute angle with each other and located symmetrically with regard to the axis of the drill. Expediently, each cutting edge located approximately in the central plane of the cutting member is formed by inclined areas of the edges of the cutting member. The cutting member has a support with a very large surface in the drill head when the edges are located toward the center of the cutting member and pertaining to the inclined surfaces of the cutting plate are located at the edges of the transverse slot so that only the inclined areas protrude. ln this way an optimum design can be obtained by having the drill head provided with a conical end the conical angle of which is preferably greater than the cutting edge angle of the cutting member and/or equals the angle between the two cutting edges of the cutting member.  
  For further improving the withdrawal of the drilling dust. the end sections of the drilling dust grooves extend into the conical end ofthe drill head while preferably its end edges are located directly adjacent to the edges of the transverse slot and approximately parallel thereto. With a particularly advantageous design of the drill according to the invention, the conical end of the drill head is arranged in spaced relationship to the bolt on that side thereof which faces toward the cutting edge so that the bolt may be held in the drill shank over the entire diameter thereof.  
  For obtaining a precise alignment of the cutting member with regard to the drill shank, the bottom of the transverse slot has a centering depression for engagement by a protrusion of the cutting member. This centering depression may be formed, for instance, by a V-shaped formation of the bottom of the transverse slot so that a prism-shaped centering depression will be obtained. However, it is also possible that the preferably plane bottom of the transverse slot extends approximately at a right angle to the axis of the drill, while preferably approximately in the center of the length of the drill the bottom has the centering depression which may, for instance, be of rectangular contour. A corresponding projection on the cutting member is associated with the centering depression.  
  A particularly advantageous further development of the invention consists in that the cutting member which is approximately centrally symmetrical and designed as a reversible plate has at least two preferably diametrically oppositely located cutting edges so that one and the same cutting member, by being turned over, can be employed a plurality of times. If only two cutting edges are provided which are located opposite to each other. the edges of the reversible plate which interconnect the two cutting edges are shorter than the cutting edges so that the depth of the transverse slot need only be relatively small.  
  It is also possible that all edges of the preferably hexagonal reversible plate are designed as cutting edges so that, for instance, three cutting blades with two cutting edges each are available.  
  With the drill according to the invention the bolt may be used merely for preventing the loss of the cutting part, whereas when working with the drill the bolt has for all practical purposes not to absorb any forces because the drilling forces occurring during the working with the drill press the cutting part into the drill shank and, more specifically, into the transverse slot. in order to assure that only the cutting plate is exposed to wear and that as little of the shaft of the drill as possible is exposed to wear, the cutting part protrudes laterally beyond the circumference of the drill head, preferably by less than the width of the inclined surfaces forming the cutting edges.  
  Referring now to the drawings in detail and, more specifically to FIGS. 1-4, the drill illustrated therein comprises a drill shank l which is provided with a helical groove 2 for the drilling dust. At its working end, the drill has a drill head 3 in front of which the groove 2 ends in such a way that the drill head has a relatively large cross section. The end 4 of the drill head 3 is conical with an obtuse angle. In the drill head 3, symmetrically with regard to an axial plane of the drill shank 1 there is provided a transverse slot 5. The bottom 6 of slot 5 is, when viewed at a right angle to the lateral surfaces 7 of the slot 5, symmetrical with regard to the axis of the drill and is V-shaped with an obtuse angle. The V-angle of bottom 6 substantially equals the conical angle of the end 4 of the drill head 3. The bottom 6 of the transverse slot 5 is in cross section V-shaped with an acute angle. In the drill head 3 at a right angle to the central plane of the transverse slot 5 there is provided a passage bore 8 the central axis of which intersects the axis of the drill. The bore 8 is approximately in the middle between the tips of the end 4 of the drill head 3 and of the bottom 6 of the transverse slot 5 located in such a way that it is arranged outside the end 4 of the drill head 3 and, more specifically, in that section thereof which is substantially cylindrical. Diagonally or diametrically on both sides of the transverse slot 5, two end sections 9, 10 of the groove 2 are located opposite to each other. These end sections 9, 10 are located symmetrically with regard to a common axial plane of the drill shank l in such a way that one leg 11 each of its rectangular V-shaped cross section is parallel to the central plane of the transverse slot 5 while the other leg 12 is located parallel to the central axis of bore 8. The legs 11 are directly adjacent to the respective pertaining edge 13 which is formed by the corresponding lateral surface 7 of the transverse slot 5 and the conical mantle surface of the end 4 of the drill head 3, the legs .being parallel to the edge 13. One groove end section 9 is angled off and merges with that end of the helical groove 2 which is adjacent the drill head 3, whereas the other groove section is located in spaced relationship to this end and merges with the helical groove 2.  
  Inserted into the transverse slot 5 of the drill head 3 is a centrally symmetrical flat cutting plate 14 which has lateral surfaces 15 arranged parallel to each other and substantially over its entire surface engages the lateral surfaces 7 of the transverse slot 5. The cutting plate 14 which in view forms a regular hexagon has six cutting edges 16 which form acute angles with each other and merge with each other. These cutting edges 16 are each formed by two flat portions 17 of the edges of the cutting plate 14, these edges being symmetrically arranged with regard to the central plane of the plate 14. The flattened portions 17 form an acute angle with each other. Each two adjacent cutting edges form the drill cutting edge 18 and the drill tip 19 which is located in the axis of the drill. The cutting edges 16 which are parallel to each other are spaced from each other by a distance slightly greater than the diameter of the drill head 3 or drill shank 1 and in such a way that two cutting edges 16 each are provided slightly beyond the circumference of the drill head 3 and are located in an axis-parallel manner with regard to the drill.  
  The V-shape of the bottom 6 of the transverse slot 5 as well as its V-shaped cross section are so selected that with the cutting blade 14 inserted, two cutting edges 16 as well as their pertaining flattened portions 17 engage the bottom 6 substantially over their entire surface and thus form a centering protrusion 20 by means of which the cutting plate is secured against accidental lateral displacement in the transverse slot 5. With the inserted cutting plate, the inner edges 21 of the flattened portions 17 forming the cutting blade 18 are located over their entire length at the edges 13 of the transverse slot 5, whereas the inner edges 21 of the flattened portions 17 of the cutting edge 16 which is parallel to the axis of the drill are located within the lateral edges 22 of the transverse slot 5.  
  The cutting plate 14 has in its central axis a passage bore 23 the diameter of which is from 1.2 to 2.5 times greater than the diameter of the drill 8. In this bore 23 there is inserted an elastic rubber sleeve 24, preferably under preload. The inner bore of the rubber sleeve 24 has a diameter which substantially equals in size the bore 8 or is smaller than the latter. The inner bore 25 is located coaxially with regard to the outer circumference of the sleeve 24. When the cutting plate 14 is inserted, its bore 23 is by a predetermined eccentricity further removed from the bottom 6 of the transverse slot 5 than the bore 8 of the drill head 3. The inserted cutting plate 14 is held by means ofa pin 26 which has its end pressed into the bore 8 of the drill head 3. Pin 26 is passed through bore 25 of the rubber sleeve 24 in such a way that the inner bore 25 of the rubber sleeve 24 is coaxial with the bore 8 so that the rubber sleeve 24 is braced in this direction toward the bottom 6 of the transverse slot 5. In this way the cutting plate 14 is pressed elastically against the bottom 6 of the transverse slot 5. After the pin 26 has been knocked out at least partially, the plate 14 can be removed from the transverse slot 5 and can then be turned about its axis and can again be inserted and secured by the pin 26 so that other cutting edges 16 of the cutting plate 14 will now form the cutting edge of the drill. The axial extension of the rubber sleeve 24 is in thespecific embodiment shown in the drawings equalling the thickness of the cutting plate 14 while the rubber sleeve 24 may be adherently connected to the cutting plate 14.  
  As will furthermore be seen from FIG. 4, when viewing in axial direction toward the drill, the cutting plate 14 and the pin 26 are located relative to each other at a right angle and in a cross-like manner while the groove end sections 9, 10 are provided in two diametrically oppositely located corners of this cross in such a way that their lateral surfaces are arranged in spaced relationship to the cutting plate 14 and the pin 26. The diameter of pin 26 is only slightly less than the thickness of the cutting plate 14.  
  According to the embodiment illustrated in FIG. 5, in all four corners of the cross passing through the cutting plate 14a and the pin 26a there are provided groove end sections 9a, 10a in such a way that always two groove end sections 90, 10a are located diametrically opposite to each other and symmetrically to a common axial plane of the drill or drill head. Accord ing to the embodiment of FIGS. 1-4 and, more specifically, however, with the embodiment of FIG. 5, instead of one groove for the drilling dust also two helical drilling dust grooves may be provided.  
  The cutting plate 14b is, in conformity with FIGS. 6 and 7, provided with only two cutting members 18b each having two cutting edges; 16b arranged at an angle with regard to each other. These two cutting members 18b are located opposite to each other and symmetrically with regard to a common axial plane of the cutting plate 14b. The lateral edges 27 of the cutting plate 14b which interconnect the cutting members 18b are located parallel to each other and while being plane over the entire thickness of the cutting plate 14b are shorter than the cutting edges 16b.  
  According to the embodiment illustrated in FIGS. 8-10, the cutting plate 14c is provided with only one single cutting member 180. For this reason the cutting plate 14c is not designed as reversible plate. The transverse slot 5c provided in the drill head 30 of the drill shank It&#34; has a bottom 60 which is substantially plane and extends at a right angle with regard to the drill axis. The bottom 60 is provided at the center of its length with a rectangular, circular or oval centering depression 28 which extends over the entire width of the transverse slot 5c. At that edge which faces away from the cutting member 180 which latter is formed by two cutting edges arranged at an angle with regard to each other, the cutting plate is provided with a centering protrusion 20c which fits into the centering depression 28. The arrangement is such that the cutting plate 14c rests on both sides of the centering protrusion 20c with its corresponding edge on the bottom 60 of the transverse slot 5c. Provided in the cutting plate 14c is a passage bore 230 the diameter of which is approximately equal to the diameter of the passage bore 8: in the drill head 3c in such a way that the pin 26c is pressed directly into the cutting plate 140. The distance between the pin 26c from the bottom 6c of the transverse slot 50 is with this embodiment smaller than the distance of the pin 26c from the cutting member 18c or from the cutting tip 19c.  
  The embodiment according to FIGS. 11 and 12 differs from that of FIGS. 8 10 primarily in that the pin 26d which has the shape of a clamping pin is parallel to the plane of the cutting plate 14d while the cutting plate 14d has one lateral surface 15d provided with a groove 23d and the transverse slot 5d has the pertaining lateral surface 7d likewise provided with a groove 8d. The grooves 23d, 8d form with the inserted cutting plate 14d a bore-like passage for the bolt 26d. The depth of groove 9d is greater than half the diameter of the pin 26d to such an extentthat this groove can be designed as an undercut-groove and will alone suffice for guiding and holding the pin 26d pressed thereinto. The radius of curvature of the cross section of groove 23d in the cutting blade 14d is slightly greater than the radius of curvature of the cross section of pin 26d, while the longitudinal central plane of groove 23d is furthermore slightly farther spaced from the bottom of the transverse slot d than is the longitudinal central plane of the groove 8d so that the pin 26:! substantially engages only that lateral surface of groove 23d under preload which is located toward the bottom of the transverse slot 5d, whereby the cutting plate 1411 is pressed against the bottom of the transverse slot 5d.  
  As is furthermore evident from FIGS. 11 and 12, with this embodiment the drill shank 1d, instead of being provided with drilling dust grooves, has two lateral axisparallel flattened portions 2d which are parallel to the cutting plate 14d and which extend over the entire length of the drill shank 1d up to the end of the drill head 3d.  
  As shown in FIG. 13, the bottom surface 28e provided for engagement with the cutting plate l4e may also be formed by a separate insert member 29 consisting of hard metal. The insert member 29 is arranged in the head 3e of the drill 1e. The insert member 29 is likewise plate-shaped and has a thickness which approximately equals the thickness of the cutting plate 14e. The insert member 29 is arranged in the transverse slot in the drill head 3e which thus is deeper by the height of the insert member 29. The bottom surface 6e of this transverse slot, which over its entire height has plane side walls, is in the shape of a pitch circle curved concavely while the axis of curvature is spaced from the drill head 3e and intersects at a right angle the axis of the drill head 3e so that the bottom surface 6e can be manufactured in a simple manner by a side milling cutter. That surface of the insert member 29 which over its entire surface engages the bottom surface 6e of the transverse slot is curved correspondingly so that the drill head 3e and the insert member 29 are centered relative to each other when the cutting plate Me is inserted. The insert member 29 may, however, also be connected in the transverse slot by soldering, pressing. welding as well as by ultrasound or electron beam weldmg.  
  In the center of the slot bottom provided for engagement with the cutting plate, there is furthermore provided a bore for manufacturing reasons. If, however, the member containing the transverse slot is pressed in later, the said bore will be superfluous. With the embodiment according to FIG. 13, it is possible better to absorb the high forces occurring in the bottom of the slot.  
  It is, of course, to be understood that the present invention is, by no means, limited to the particular showing in the drawings but also comprises any modifications within the scope of the appended claims.  
 What is claimed is:  
  I. In a drill for masonry and rock; a drill shank having a working end, longitudinally extending dust groove means formed in said shank and extending along the shank from said working end, a transverse slot formed in the working end of said shank, a cutting plate formed of hard wear resistant material seated in said slot, and a retaining pin extending through said shank substantially perpendicular to the axis of said shank and also engaging said cutting plate and retaining said plate in said slot. said pin being moveable in said shank in the axial direction of said pin to release said cutting plate from said slot, said cutting plate being polygonal when viewed in a direction perpendicular to the plane thereof, at least the axially outer end of the cutting plate having a point on the axis of the drill shank and inclining rearwardly from the point in, both directions when viewed perpendicular to the plane of the cutting plate, the said outer end of the cutting plate being bevelled on opposite sides to form cutting edges thereon, the working end of said shank being conical and tapering inwardly, there being a bottom and side edges of the open end of said slot meeting where the slot intersects the conical end of the shank being in about the planes of the bevels on the outer end of said cutting plate, the angle on the working end of the drill shank being greater than the angle between the bevels on the outer end of said cutting plate, said groove means in said shank comprising a terminal portion at the working end of said shank disposed immediately forward of the leading side of said cutting plate at each lateral end thereof.  
  2. A drill according to claim 1 in which said pin is generally centrally located with respect to said cutting plate and is perpendicular to the plane of the cutting plate and extends through said cutting plate.  
  3. A drill according to claim I in which said pin is substantially parallel to the plane of said cutting plate.  
  4. A drill according to claim 1 in which the axis of said pin intersects the axis of said shank.  
  5. A drill according to claim 1 in which said pin is disposed along said shank between the conical end thereof and the bottom of said slot.  
  6. A drill according to claim 1 in which said cutting plate is symmetrical about at least one central axis which is parallel to the plane of the cutting plate and perpendicular to the axis of the shank when the cutting plate is seated in said slot, each edge of the cutting plate facing away from said central axis having a cutting edge formed thereon, the bottom of said slot being formed for supportingly engaging the axially inner cutting edge while the axially outer cutting edge is in working position.  
  7. A drill according to claim 1 in which said slot is formed with a centering recess therein and said cutting plate has a protrusion thereon which engages said recess when the cutting plate is positioned in said slot.  
  8. A drill according to claim 7 in which the bottom of said slot is perpendicular to the axis of said shank and said centering recess is in the middle of the length of the bottom of said slot.  
  9. A drill according to claim 7 which includes a hard insert member in said slot and forming the bottom thereof.  
  10. In a drill for masonry and rock; a drill shank having a working end, longitudinally extending dust groove means formed in said shank and extending along the shank from said working end, a transverse slot formed in the working end of said shank, a cutting plate formed of hard wear resistant material seated in saidslot, and a retaining pin extending through said shank substantially perpendicular to the axis of said shank and also engaging said cutting plate and retaining said plate in said slot, said pin being moveable in said shank in the axial direction of said pin to release said cutting plate from said slot, the bottom of said slot being in the form of a segment of a cylinder having an axis disposed outwardly from the working end of the shank and intersecting the axis of the shank at a right angle.  
  11. drill according to claim in which said shank has a drilled hole therein into which said pin closely fits.  
  12. A drill according to claim 10 in whichsaid shank has a transverse hole therein parallel tov the plane of said slot and offset laterally from the axis of said shank,  
 said pin closely fitting said hole and on one side extending into said slot, said cutting plate having a groove formed in the side facing said pin to receive said pin.  
  13. A drill according to claim .10 in which a groove is formed along one side ofsaid slot perpendicular to the axis of said shank, said cutting plate having a groove formed therein on the side facing the groove in the shank and in registration&#39;therewith, said grooves forming a space to receive said pin.  
  14. A drill according to claim 10 in which said cutting plate is polygonal when viewed in a direction perpendicularto the plane thereof, at least the axially outer end of the cutting plate having a point on the axis of the drill shank and inclining rearwardly from the pointin both directions when viewed perpendicular to the plane of thecutting plate, the said outer end of the cutting plate being bevelled on opposite sides to form cutting edges thereon, the working end of said shank being conical and tapering inwardly, the side edges of the open end of said slot meeting where the slot intersects the conical end of the shank being in about the planes of the bevels on the outer end of said cutting plate.  
  15. A drill according to claim 10 in which said cutting plate when viewed perpendicular to the plane thereof is a regular polygon, all of the edges of said cutting plate being bevelled to form a cutting edge extending about&#39;the entire periphery of said cutting plate, said I plate being angularly indexable in said slot for successively presenting different regions of the periphery thereof to working position.  
  .16. A drill according to claim 10 in which said cutting plate protrudes laterally beyond the limits of said shank. the protruding regions of said cutting plate being bevelled.  
  17. In a drill for masonry and rock; a drill shank having a working end, longitudinally extending dust groove means formed in said shank and extending along the shank from said working end, a transverse slot formed in the working end of said shank, a cutting plate formed of hard wear resistant material seated in said slot, a retaining pin extending through said shank substantially perpendicular to the axis of said shank and also engaging said cutting plate and retaining said plate in said shallow than the groove in said shank.  
 18. A drill according to claim 17 in which said pin is offset from the center of said cutting plate for preload toward the bottom of said slot.  
 lill  
  19. A drill according to claim 17 in which said cutting plate has a central hole, an elastic bushing member in said hole, said pin extending perpendicular to the plane of said cutting plate and through said elastic bushing member.  
  20. A drill according to claim 17 in which said pin is radially resilient and has a diameter slightly less than the thickness of said cutting plate.  
  21. A drill according to claim 17 in which said cutting plate engages the bottom of said slot across the entire diameter of said shank.  
  22. A drill according to claim 17 in which said slot is circumferentially spaced from the dust groove means when the drill is viewed axially at the working end, the working end of said dust groove means being substantially in the form of a right angle V-shaped notch means.  
  23. A drill according to claim 17 in which said dust groove means comprises at least one helical groove formed in the drill shank, said helical groove extending to near the working end of the shank, a pair of diametrally opposed ax-ial grooves formed in said shank and extending from the working end thereof to and intersecting said helical groove, the plane of said axial grooves being at an angle of about 45 degrees to the plane of said cutting plate. 7  
  24. A drill according to claim 17 in which said dust groove means comprises a pair of diametrically opposite helical grooves in said shank.  
 25. A drill according to claim 17 in which said dust groove means comprises at least one helical groove formed in the drill shank, said helical groove extending to near the working end of the shank, and an axial groove formed in the drill shank and extending from the working end of the shank to and intersects the said helical groove to form a continuous passage for dust.  
  26. A drill according to claim 24 in which the helical dust groove extends toward the working end of the shank beyond the region of intersection thereof with said axial groove.  
  27. In a drill for masonry and rock; a drill shank having a working end. longitudinally extending dust groove means formed in said shank and extending along the shank from said working end, a transverse slot formed in the working end of said shank, a cutting plate formed of hard wear resistant material seated in said slot, and a retaining pin extending through said shank substantially perpendicular to the axis of said shank and also engaging said cutting plate and retaining said plate in said slot, said pin being moveable in said shank in the axial direction of said pin to release said cutting plate from said slot, said cutting plate being symmetrical about at least one central axis which is parallel to the plane of the cutting plate and perpendicular to the axis of the shank when the cutting plate is seated in said slot, each edge of the cutting plate facing away from said central axis having a cutting edge formed thereon. the bottom of said slot being formed for supportingly engaging the axially inner cutting edge while the axially outer cutting edge is in working position, the cutting edges of said cutting plate being V-shaped and bevelled and the edges of the cutting plate perpendicular to said central axis being shorter than the other edges of the cutting plate.  
  28. In a drill for masonry and rock; a drill shank having a working end, longitudinally extending dust groove means formed in said shank and extending along the shank from said working end, a transverse slot formed in the working end of said shank, a cutting plate formed of hard wear resistant material seated in said slot, and a retaining pin extending through said shank substantially perpendicular to the axis of said shank and also engaging said cutting plate and retaining said plate in said slot, said pin being moveable in said shank in the axial direction of said pin to release said cutting plate from said slot, said cutting plate when viewed perpendicular to the plane thereof being a regular polygon, all of the edges of said cutting plate being bevelled to form a cutting edge extending about the entire periphery of said cutting plate, said plate being angularly indexable in said slot for successively presenting different regions of the periphery thereof to working position, said cutting plate being hexagonal and when seated in said slot having a pair of edges parallel to the axis of the shank.  
  29. A drill according to claim 28 in which said pair of edges protrude beyond the shank at the sides a distance about equal to the height of the bevels thereon.  
  30. In combination with a rock drill having a drill shank which provides a transverse slot at the drill head thereof including a bottom and a cutting blade of hard metal installed interchangeably and secured with a pin lying approximately at right angles to axis of the drill, the pin engaging in bores of the drill shank and cutting blade which fits in axial direction of the drill under preload against the bottom, the improvement therewith which comprises an elastic sleeve arranged between the pin and one of the bores, said elastic sleeve under preload pressing the cutting blade against the bottom of the slot, said elastic sleeve lying symmetrically to the drill axis and at right angles to a plane of the cutting blade installed in the transverse slot.  
  31. A drill in combination according to claim 30. in which said elastic sleeve is installed with preload in the bore of the cutting blade.  
  32. A drill in combination according to claim 30. in which said elastic sleeve forms a bore for insertion of the pin and said elastic sleeve is installed in a bore larger than the borefor the pin.  
  33. In combination with a rock drill having a drill shank which provides a transverse slot at the drill head thereof including a bottom and a cutting blade of hard metal installed interchangeably and secured with a pin lying approximately at right angles to axis of the drill, the pin engaging in bores of the drill shank and cutting blade which fits in axial direction of the drill under preload against the bottom, the improvement therewith which comprises an elastic sleeve arranged between the pin and one of the bores, said elastic sleeve under preload pressing the cutting blade against the bottom of the slot, said&#39;elastic sleeve forming a bore for insertion of the pin and said elastic sleeve being installed in a bore larger than the bore for the pin, said elastic sleeve being adhered to an inner surface of the pertaining bore.  
  34. A drill in combination according to claim 33, in which said elastic sleeve is installed in the bore of the cutting blade.  
  35. A drill in combination according to claim 34. in which said elastic sleeve is a rubber cylinder.  
  36. In combination with a rock drill having a drill shank which provides a transverse slot at the drill head thereof including a bottom and a cutting blade of hard metal installed interchangeably and secured with a pin lying approximately at right angles to axis of the drill. the pin engaging in bores of the drill shank and cutting blade which fits in axial direction of the drill under preload against the bottom, the improvement therewith which comprises an elastic sleeve arranged between the pin and one of the bores, said elastic sleeve under preload pressing the cutting blade against the bottom of the slot, said elastic sleeve forming a bore for insertion of the pin and said elastic sleeve being installed in a bore larger than the bore for the pin, the bore for said elastic sleeve having an undersized diameter for engagement of the pin.