US3753320A

US3753320A - Apparatus for grinding drills

Info

Publication number: US3753320A
Application number: US00060888A
Authority: US
Inventors: R Wurscher
Original assignee: INTERMEDIUM AG
Current assignee: INTERMEDIUM AG
Priority date: 1967-05-03
Filing date: 1970-08-04
Publication date: 1973-08-21
Anticipated expiration: 1990-08-21
Also published as: SE325210B

Abstract

Apparatus is described whereby the clearance surfaces of the working head of a drill are ground by keeping the drill axis at an operatively constant angle relative to the rotary place of a grinding wheel, while rotating the drill about its longitudinal axis within a limited angular area. In one embodiment of the invention the wheel heel is provided with a single grinding surface and may be mounted stationary or mounted to yield against spring pressure to a single clearance surface urged against it, until the other clearance surface is intercepted by an abutment upon which it rests while rotating the drill, thus providing an essentially steady grinding pressure. In the latter case, the point of the drill will be centrically ground after working each clearance surface for an equally long time. In a modified form the wheel is provided with two conical grinding surfaces and a slight clearance between these surfaces. Thereby a centrically ground point of the drill is automatically achieved.

Description

United States Patent [1 1 Wurscher APPARATUS FOR GRINDING DRILLS [75] Inventor: Raimund August Wurscher, Lund,

Sweden [73] Assignee: Intermedium AG, Luegisland,

Sweden [22] Filed: Aug. 4, 1970 [21] Appl. No.: 60,888

Related US. Application Data [30] Foreign Application Priority Data May 3, 1967 Sweden 6201/67 [52] US. Cl 51/73 R, 51/102, 51/128, 51/219 R [51] Int. Cl. B241) 3/26 [58] Field of Search 51/73 R, 102, 128, 51/219 R, 241 R 5 6] References Cited UNITED STATES PATENTS 1,231,258 6/1917 Horvath 5l/2l9RX 1,994,975 3/1935 Wil1iams..... 51/73 R UX 2,017,532 10/1935 Elter et a1... 51/219 R X 2,372,794 4/1945 Ricks 51/219 R X 2,424,470 7/1947 Kronwall..... 51/219 R X 2,540,320 2/1951 Cayo 51/73 R X 2,591,893 4/1952 Trippel.... 51/219 R X 2,601,748 7/1952 Lohr 51/219 R X I I '2 x 1 l3 1 II 1 Aug. 21, 1973 Perra 51/219 R X Primary Examiner-Donald G. Kelly Attorney-Jacobs & Jacobs [57] ABSTRACT Apparatus is described whereby the clearance surfaces of the working head ofa drill are ground by keeping the drill axis at an operatively constant angle relative to the rotary place of a grinding wheel, while rotating the drill about its longitudinal axis within a limited angular area. In one embodiment of the invention the wheel heel is provided with a single grinding surface and may be mounted stationary or mounted to yield against spring pressure to a single clearance surface urged against it, until the other clearance surface is intercepted by an abutment upon which it rests while rotating the drill, thus providing an essentially steady grinding pressure. In the latter case, the point of the drill will be centrically ground after working each clearance surface for an equally long time. In a modified form the wheel is provided with two conical grinding surfaces and a slight clearance between these surfaces. Thereby a centrically ground point of the drill is automatically achieved.

32 Claims, 7 Drawing Figures msmcomz I m 3753.320 sum 1 0F 33 INVENTOR RAIMUND AUGUST WURSCHER ATTORNEYS mcmznwm m 3.753.320

sum 3 BF 3 PEG. 2

INVENTOR RAIMUND AUGUST WURSCHER FIG. 5 BY A a! ATTORNEYS l APPARATUS FOR GRINDING. DRILLS.

This application is a continuatiomin-part of application Ser. No. 682,406, filed Nov. 13, 1967, now abancloned, and of application Ser. No. 27,589, filed Apr. 13, 1970, now abandoned, which, in turn, is a continuation-in-part of said application Ser. No. 682,406 and of application Ser. No. 864,445, filed Oct. 7, 1969, now abandoned.

The present invention relates to an app ratus for grinding drills, more particularly spiral drills.

In order that a drill may operate, quickly and efficiently and have a long life, it is necessary to. grind the working head. of the drill in a correct manner. In.-. creased drilling costs and faulty bores are mostly caused by faulty grinding of the drill. Machine grinding is the most exact method of grinding drills, and'when a drill is carefully machine ground it will cut morev quickly, have a longer life and drill agreater number of exact bores than if it is ground manually. The most important factors for the efficiency of a drill, are. the point angle, the clearance angle, and the angle between the main cutting edges and the transversal cutting edge of the drill head, the so-called transversal cutting edge angle. All these angles may be affected by the grinding of the drill head, is. at the grinding of the clearance sur face for each main cutting edge of the drill head.

In known apparatus for grinding drills it is generally necessary to clamp fast the drill to be ground, and the, known apparatus require either greater manual skill or else do not permit the drill head tooccupy the most advantageous clearance and transversal cutting edge angles.

An object of the invention is to provide an apparatus for grinding drills which does not make it necessary to clamp fast the drill which is. being ground, but which will nevertheless guide, the drill, thereby achieving correct grinding of the drill head,

Another object of the invention is to provide an apparatus for grinding drills of different diameters without readjusting the apparatus.

With the invention is provided an apparatus for grinding drill heads having at least one main cutting edge and, in related cases, a transversal cutting edge intersecting the main cutting edges, and a clearance surface and a flute for each main cutting edge, comprising a rotating grinding wheel provided with one or two grinding surfaces and at least one set of guiding means for guiding a drill in relation to the wheel, the guiding means having means for providing an essentially constant operative angle between the geometrical longitudis nal axis of the drill and the rotary plane of the wheel and admitting a rotation of the drill about said axis, and means. li i g sa d o at on o ha a c earanc surface ill be w p but by a r ng u ace at such n relative to said grinding surface that the intended clearance angle of the clearance surface is achieved.

In the preferred embodiment of the invention the guiding means of each said set consists of a cylindrical guiding passage provided in a guiding element and at least one guide lug mounted in the guiding passage for fitting into a flute of the drill.

The drill to be ground is inserted into the guiding passage in between the guide lugs, pressed against the grinding surface or surfaces while simultaneously rotated in a reciprocating rotary movement limited by the guide lugs.

Where the grinding wheel is provided with one grinding surface, the grinding operation has to be repeated for each clearance surface and, in order to achieve a centered point of the drill, each clearance surface has to be ground for an equally long time under the same grinding pressure. For achieving a steady grinding pressure, the wheel is preferably mounted so as to resiliently yield to a drill urged against the grinding surface, at which the advance of the 'drill is'intercepted by an abutment for engaging a clearance surface not engaging the grinding surface; thus centering the drill point is, permitted by grinding the clearance surfaces for an equally long time.

Where the grinding wheel is provided with two grinding surfaces, the common standard drill, having two clearance surfaces, will, regardless of grinding pressure or grinding time, be automatically centered. Where providing a slight clearance between said two grinding surfaces, the transversal cutting edge angle will be considerably improved.

In the accompanying drawings:

FIG. 1 a is a longitudinal section of an apparatus showing a grinding wheel provided with one grinding surface while grinding one clearance surface of a drill;

FIG. lb is a longitudinal section of an apparatus showing a grinding wheel provided with two grinding surfaces while grinding the clearance surfaces of a drill;

FIG. 1c is a longitudinal section of another embodiment of the invention;

FIG. 2 is a plan view on a larger scale of a guiding passage having guide lugs for limiting the rotation of the drill;

FIGS. 3 and 4 show the same detail as FIG. 2 although with the working head of the drill drawn in the two limiting positions of the rotational movement occurring during the grinding operation, the plan view of FIGS. 2 to 4 being seen in a direction towards the grinding wheel from the base of the drill; and

FIG. 5 is a plan view of the working head of the drill.

The drill 1 shown in the drawings is assumed to be held and handled manually during the grinding operation. The main parts of the grinding apparatus are enclosed in a tubular housing 2 open at both ends. The housing is inserted into and attached to a flange 4 screwed into. the front wall of an electric motor 3. In FIG. la the grinding wheel 5 has one conical grinding surface and is fixed to a tubular grinding wheel shaft 6 by means of a nut 7. The grinding wheel shaft 6 is threaded onto the driving shaft 8 of the electric motor 3 so that their two longitudinal axes will coincide with the longitudinal axis of the tubular housing 2 and will be parallel to the longitudinal axis of the drill head 1. The grinding wheel shaft 6 and consequently also the grinding wheel 5 are axially movable in relation to the driving shaft 8 of the electric motor 3 and are urged by spring 9 in the direction of the head of the drill 1. Power is transmitted to the grinding wheel shaft 6 by means of a pin 10 fixed to the grinding wheel shaft 6 and engaging with a slot 11 provided in the end of the driving shaft 8. Into the end of the housing 2 which is remote from the motor 3 there is introduced a cylindrical guiding element 12 fixed with a clamping screw 13. The guiding element 12 has cylindrical guiding passages at the same center distance from and parallel to the grinding wheel shaft 6, for guiding drills of different diameters, two of which, 14 and 15, are shown in FIG. 121. At the end of the guiding element 12 which is remote from the grinding wheel 5 there is provided an abutment element 16 common to all guiding passages 14, and intended for that clearance surface of the drill head which is not in contact with the grinding wheel 5. The abutment element 16 has an oblique surface extending along a helical line, the central axis of which coincides with the rotational axis of the grinding wheel 5 and the peripheral radius of which is slightly shorter than the radius of the circle cutting the center axes of all guiding

passages

14, 15.

The widest guiding passage is directed towards that point of the face of the abutment element 16 which is nearest to the grinding wheel 5, while the narrowest guiding passage is directed towards that point of the said face which is most remote from the grinding wheel 5 as urged to its remotest distance from the guiding element l2, and the other guiding passages are distributed between the widest and the smallest one according to their diameters. This provides for a correct setting of the drill heads in relation to the grinding wheel and for approximately the same stable grinding pressure, irrespective of the different diameters of the drill heads.

At the ends of the guiding passages which are directed to the face of the abutment element 16, there are provided two guide lugs 17, 18 (FIG. 2) each fitting into one of the two spiral flutes of the drill 1. These are two trapezoidal mirror images of each other, displaced rotationally through 180 and each extending inwards approximately one fourth of a guiding passage diameter towards the center of the guiding

passage

14,15 They have each two straight abutment margins extending along two different guiding passage diameters having a relative angle of 60 and are oriented so as to be symmetrically mirrored at each side of the radius 19 of the grinding wheel 5 through the center axis of the respective guiding

pasasge

14, 15. They are disposed at a distance from the corresponding part of the face of the abutment element 16 which is equivalent to an angular difference of 2 between the drill diameter that meets the extreme corners of the main cutting edges 20 and the drill diameter meeting the guiding margins of the flutes of the drill in the limiting plane of the guide lugs 17 and 18 through their abutment margins.

The distance of the abutment element 16 to the guiding pins 17 and 18 may be adjusted by turning a knob 23 at the upper end of a shaft 22 carrying the abutment element 16. Into the central portion of the shaft 22 there is screwed an abutment 24 for the grinding wheel shaft 6, limiting the resilient movement of the grinding wheel in a direction towards the guiding element 12 when no drill is being ground.

The drill I inserted into a guiding passage suitable therefor is pressed for grinding one of its clearance surfaces against the face of the abutment element 16 while simultaneously rotated in a reciprocating rotary movement so limited by the guide lugs 17 and 18 that the diameter of the drill which meets the extreme comers of its main cutting edges 20 in the two limiting positions of the rotary movement forms the angles of about 62 (,8, in FIG. 3) and 32 (B, in FIG. 4) with the radius 19 of the grinding wheel through the center of the drill 1, at which a transversal cutting edge angle of about 50 y in FIG. 5) is obtained. Thereby a clearance angle of about 12 is obtained, somewhat depending on the diameter of the grinding wheel, its pitch angle a, etc. When the distance between the abutment element 16 and the guide lugs 17 and 18 is changed by means of the knob 23, the guide lugs will engage with a portion of the drill flutes that is located higher or lower, and the angular area within which the clearance surface being ground can be rotated, will be tuned in relation to the radius 19 of the grinding wheel so that other clearance angles may be obtained.

If the power with which the spring 9 urges the grinding wheel 5 against the working end of the drill is the same for drills of different diameters, the grinding pressure and consequently the grinding action in the longitudinal direction of the drill is approximately inversely proportional to the square of the drill diameter. This may, however, entail difficulties when centering small drill heads, since the centering is achieved by grinding both clearance surfaces for an equal length of time and is thus dependent on time. It is therefore desirable that the grinding pressure is-not changed together with the drill diameter, which may be achieved by loading the spring 9, i.e. compressing it proportionally to the square of the drill diameter. This is possible in the above embodiment of the abutment element 16 and the collateral distribution of the guiding

passages

14, 15 in the guiding element 12, provided the uncompressed spring 9 is of suitable length.

FIG. 1b shows the embodiment of the invention wherein the grinding wheel 5 is provided with two grinding

surfaces

5a and 5b with a slight clearance 19 along the meeting circular border of these surfaces. The grinding wheel 5 is fixed to a nave 6 which, in turn, is fixed to the driving shaft 8 of the electric motor 3 so that the rotational axis of the wheel will coincide with the longitudinal axis of the housing 2 and will be parallel to the axis of the drill 1'. In the threaded end of the housing 2 which is remote from the electric motor 3, a cylindrical guiding element 12 is screwed on and fixed with a clamping screw 13. The guiding element 12 has cylindrical guiding passages, parallel with and at a common distance from the rotational axis of the wheel equal to the radius of the circular border between the internal and the external conical grinding surfaces of the wheel, for guiding drills of different diameters, two of which, 14 and 15, are shown in the drawing.

The drill I inserted into the guiding passage suitable therefor is, for grinding its clearance surfaces, pressed against the grinding surfaces as turned in a reciprocating rotary movement limited by the guide lugs, whereby the clearance surfaces move within an angular area so sized and so disposed relative to the grinding surfaces that each of the clearance surfaces will obtain the intended clearance angle.

By screwing the guiding element 12 in or out, the distance between the guide lugs 17', 18 and the grinding surfaces can be altered and other clearance angles of the clearance surfaces will be obtained.

It is to be understood that the guiding passages need not be parallel with the rotational axis of the wheel, but may be inclined to said axis at any angle. They only have to guide the drills against the grinding surfaces such as to tally with the inclination of the grinding surfaces and to guide the point of the drill onto the border between the two grinding surfaces as illustrated in FIG. lb. Accordingly, the shapes of the grinding surfaces may be other than as illustrated; for instance both of them may have an external conical shape as illustrated in FIG. 1c.

FIG. 1c employs the same reference numerals as FIGS. 1a and lb to designate like parts, but the reference numerals are double primed in FIG. 1c.

What is claimed is:

1. Apparatus for grinding drills having at least'two main cutting edges and having a clearance surface for each main cutting edge, comprising a rotatable grinding wheel provided with at most two grinding surfaces and at least one set of guiding means for guiding a drill head in relation to the wheel, the guiding means having means for providing an essentially constant operative angle between the geometrical longitudinal axis of the drill and the rotary plane of the wheel and admitting a rotation of the drill about said axis, at least one first stop means for engaging the drill and thereby preventing rotation of the drill about its axis in one direction beyond a first limiting position and at least one second stop means for engaging the drill and thereby preventing rotation of the drill about its axis in a direction opposite to said one direction beyond a second limiting position, said first and second stop means being so arranged with respect to one another and to a drill in said guiding means as to be operable to limit said rotation of said drill to a predetermined angular extent between a said first and second limiting positions such that when said drill is rotated between said limiting positions and through said predetermined angular extent while a clearance surface thereof is in contact with an associated rotating grinding surface a predetermined clearance angle and a predetermined transversal cutting edge angle are both obtained. 1

2. Apparatus according to claim 1, wherein each set of guiding means consists of a cylindrical guiding passage provided in a guiding element and said first and second stop means are provided by at least one guide lug having a pair of oppositely disposed abutment margins and being associated with the guiding passage for fitting into a flute of a drill, rotation of the drill about its axis in said one direction beyond said first limiting position being prevented by engagement of said drill with one of said abutment margins and rotation of the drill about its axis in said opposite direction beyond said second limiting position being prevented by engagement of said drill with the other abutment margin.

3. Apparatus according to claim 2, wherein there is provided a number of guiding passages and guide lugs associated therewith, which guiding passages have different diameters for guiding drills. of different diameters.

4. Apparatus according to claim 3, further provided with means whereby the wheel, by increasing resistance, resiliently recoils to the pressure exerted by at least one clearance surface urged against its corresponding grinding surface, and means for so intercepting the advance of the drill as to determine a substantially steady operative distance between the tip of the drill and the guide lugs and a stable resilient counterforce of the wheel.

5. Apparatus according to claim 4, wherein the wheel is provided with one grinding surface and the means intercepting the advance of the drill consists of an abutment for receiving the clearance surface not engaging the grinding surface.

6. Apparatus according to claim 5, wherein the abutments are united in one abutment element having a stop face advancing helically in the direction of the rotational axis of the wheel at a common distance from said axis, and wherein the guiding passages are so distributed according to their diameters over said stop face that a drill, inserted into its appropriate guiding passage and urged onto the stop face, will cause the wheel to recoil a distance which is so increased by increased drill diameter that the resilient counterforce of the wheel will produce approximately the same grinding pressure for any drill that is receivable.

7. Apparatus according to claim 6, further provided with means whereby the distance between the stop face and the guide lugs can be varied.

8. Apparatus according to claim 1, wherein the wheel is provided with two conical grinding surfaces meeting along a circular border at an angle appropriate to the point angle of the drill.

9. Apparatus according to claim 8, wherein there is a slight clearance between the grinding surfaces along the meeting circular border of these surfaces.

10. Apparatus according to claim 8, wherein each set of guiding means consists of a cylindrical guiding passage provided in a guiding element and said first and second stop means are provided by at least one guide lug having a pair of oppositely disposed abutment margins and being associated with the guiding passage for fitting into the flute of a drill, rotation of the drill about its axis in said one direction beyond said first limiting position being prevented by engagement of said drill with one of said abutment margins and rotation of the drill about its axis in said opposite direction beyond said second limiting position being prevented by engagement of said drill with the other abutment margin.

11. Apparatus according to claim 10, wherein is provided a number of guiding passages and guide lugs associated therewith, which guiding passages have different diameters for guiding drills of different diameters.

12. Apparatus according to claim 11, wherein there is a slight clearance between the grinding surfaces along the meeting circular border of these surfaces.

13. Apparatus according to claim 12, further provided with means whereby the distance between the grinding surfaces and the guide lugs is adjustable.

14. Apparatus for grinding spiral drill bits having at least one main cutting surface and having a clearance surface and a flute for each main cutting surface, comprising a rotatable grinding wheel having a grinding surface and means for connecting the wheel to a driving device and means for guiding a drill bit in relation to the grinding surface, the guiding means having means providing a constant angle between the geometrical longitudinal axis of the drill and the grinding surface during the grinding operation, at least one first stop means for engaging the drill and thereby preventing rotation of the drill about its axis in one direction beyond a first limiting position and at least one second stop means for engaging the drill and thereby preventing rotation of the drill about its axis in a direction opposite to said one direction beyond a second limiting position, said first and second stop means being so arranged with respect to one another and to a drill in said guiding means as to be operable to limit the rotational movement of the drill bit to a predetermined angular extent between said first and second limiting position such that when said drill is rotated between said limiting positions and through said predetermined angular extent while a clearance surface thereof is in contact with an associated rotating grinding surface a predetermined clearance angle and a predetermined transversal cutting edge angle are both obtained.

15. Apparatus for grinding spiral drill bits having at least one main cutting surface, a transversal cutting surface intersecting the main cutting surface and one clearance surface and a flute for each main cutting surface, comprising a rotatable wheel having a bowlshaped conical grinding surface and having means for connecting the wheel to a driving device, a guiding element fixed in relation to the rotational axis of the wheel, a number of cylindrical guiding passages having different diameters one of which is largest and one of which is smallest provided in the guiding element at equal distances from the rotational axis of the wheel and extending in parallel thereto, for guiding drill bits of different diameters in relation to the grinding surface, guiding pins in the guiding passages adapted to engage each with one of the flutes of the drill bits in order to limit the rotational movement of the drill bits between two limiting positions corresponding to the points of engagement of said flutes and said pins, said pins being so arranged with respect to one another and to a drill bit in said guiding passage as to be operable to limit said rotation to a predetermined angular extent between said limiting positions such that when said drill is rotated between said limiting positions and through said predetermined angular extent while a clearance surface thereof is in contact with an associated rotating grinding surface a predetermined clearance angle and a predetermined transversal cutting edge angle or both obtained and an abutment united with the guiding element for determining the position of the drill bits in relation to the guiding pins.

16. Apparatus as claimed in claim 15, wherein the wheel is mounted for resilience in an axial direction under the influence of the pressure from a drill bit pressed against the grinding surface, the pressure of the drill bit against the grinding surface being limited by the abutment for providing a constant grinding pressure.

17. Apparatus as claimed in claim 15, wherein the guiding passages are of essentially the same diameter as the drill bit.

18. Apparatus as claimed in claim 15, wherein the guiding pins are disposed diametrically opposite each other in the guiding passage and extend inwards approximately one fourth of a guiding passage diameter towards the center of the guiding passage and being each provided with two straight abutments margins extending along two different diameters of passage forming an angle of 60 with each other.

19. Apparatus as claimed in claim 15, wherein the distance between the abutment and the guiding pins in the direction of the geometrical axis of the wheel is adjustable in order to provide different clearance angles for the clearance surfaces of the drill bits.

20. Apparatus as claimed in claim 15, wherein the abutment is common to all guiding passages and extends along a helical turn, the center axis of which coincides with the rotational axis of the wheel and the radius of which is slightly shorter than the radius of the circle cutting the center axes of all guiding passages.

21. Apparatus as claimed in claim 15, wherein the largest guiding passage is directed towards that point of the abutment which is nearest to the grinding surface, while the smallest guiding passage is directed towards the point that is most remote therefrom, while the other the guiding guiding passages are distributed therebetween according to their diameters.

22. Apparatus for grinding drills having at least one main cutting surface and one clearance surface and a flute for each cutting surface comprising a rotatable wheel having a conical grinding surface, means connected to the wheel for driving the wheel, a guiding element, at least one cylindrical guiding passage provided in the guiding element for guiding drill bits in relation to the grinding surface, at least one first stop means in the guiding passage for engaging a flute of a drill within the guiding passage and thereby preventing rotation of the drill about its axis in one direction beyond a first limiting position and at least one second stop means in the guiding passage for engaging a flute of the drill and thereby preventing rotation of the drill about its axis in a direction opposite to said one direction beyond a second limiting position, said first and second stop means being so arranged with respect to one another and to a drill within the guiding passage as to be operable to limit the rotational movement of the drill to a predetermined angular extent between said first and second limiting positions such that when said drill is rotated between said limiting positions and through said predetermined angular extent while a clearance surface thereof is in contact with an associated rotating grinding surface a predetermined clearance angle and a predetermined transversal cutting edge angle are both obtained.

23. Apparatus as set forth in claim 22, wherein a number of cylindrical guiding passages are provided in the guiding element at equal distances from the rotational axis of the wheel and extending parallel thereto which guiding passages have different diameters for guiding drill bits of different diameters in relation to the grinding surface.

24. Apparatus as set forth in claim 22, wherein the means of the guiding passage is a pin in the guiding passage the size of which corresponds to the intended angle between the main cutting surface and the transversal cutting surface of the drill bit.

25. Apparatus as set forth in claim 22 and further including an abutment united with the guiding element for determining the postion of the drill bit in relation to the means in the guiding passage and consequently the position of the angular area in relation to the grinding surface so that the clearance surface of the drill bit will obtain the intended clearance angle when being pressed against the rotating grinding surface while rotating the drill bit within the angular area corresponding to the clearance surface.

26. Apparatus for grinding spiral drills having two main cutting edges and having a clearance surface and a flute for each main cutting edge, comprising a rotatable grinding wheel of which the grinding surface consists of an internal and an external conical part, means for guiding the clearance surfaces of the main cutting edges relatively to the grinding surface of the wehel, said means having means for guiding the drill so that the axis of the drill is parallel to and located at a distance from the axis of the grinding wheel which is equal to the radius of the circular intersection between the internal and the external conical part of the grinding surface, at least one first stop means for engaging the drill and thereby preventing rotation of the drill about its axis in one direction beyond a first limiting position and at least one second stop means for engaging the drill and thereby preventing rotation of the drill about its axis in a direction opposite to said one direction beyond a second limiting position, said first and second stop means being so arranged with respect to one another and to a drill in said guiding means as to be operable to limit rotary movement of the drill about its axis to a predetermined angular extent between said first and second limiting positions such that when said drill is rotated between said limiting positions and through said predetermined angular extent while a clearance surface thereof is in contact with an associated rotating grinding surface a predetermined clearance angle and a predetermined transversal cutting edge angle are both obtained.

27. Apparatus as claimed in claim 26, wherein the grinding wheel is axially movable against a resilient force and wherein the means limiting the rotary movement of the drill about its axis join the axisl movement of the grinding wheel.

28. Apparatus as claimed in claim 26, wherein the distance in the direction of the axis of the grinding wheel between the means limiting the rotary movement of the drill and the grinding wheel is adjustable.

29. Apparatus for grinding drills having at least one main cutting edge and having a flute and a clearance surface for each main cutting edge, comprising a rotatable grinding wheel having a grinding surface, means for guiding the clearance surfaces of the main cutting edges relative to the grinding surface of the wheel, said means having means for guiding the drill so that the axis of the grinding wheel and the axis of the drill are located in two mutually fixed straight lines during the grinding operation at least one first stop means for engaging the drill and thereby preventing rotation of the drill about its axis in one direction beyond a first limiting position and at least one second stop means for engaging the drill and thereby preventing rotating of the drill about its axis in a direction opposite to said one direction beyond a second limiting position, said first and second stop means being so arranged with respect to one another and to a drill in said guiding means as to be operable to limit rotary movement of the drill about its axis to a predetermined angular extent between said first and second limiting positions such that when said drill is rotated between said limiting positions and through said predetermined angular extent while a clearance surface thereof is in contact with an associated rotating grinding surface a predetermined clearance angle and a predetermined transversal cutting edge angle are both obtained.

30. Apparatus as claimed in claim 29, wherein the grinding wheel is mounted for resilience under the influence of the pressure from a drill pressed against the grinding surface, and wherein the means limiting the rotary movement of the drill about its axis join the resilient movement of the wheel.

31. Apparatus as claimed in claim 29, wherein the axial travel of the drill against the resiliently movable grinding wheel is limited by an abutment engaging the clearance surface of the drill bit not engaging with the grinding surface of the wheel.

32. Apparatus as claimed in claim 30, wherin the distance between the means limiting the rotary movement of the drill about its axis and the grinding surface of the wheel is adjustable.

Claims

1. Apparatus for grinding drills having at least two main cutting edges and having a clearance surface for each main cutting edge, comprising a rotatable grinding wheel provided with at most two grinding surfaces and at least one set of guiding means for guiding a drill head in relation to the wheel, the guiding means having means for providing an essentially constant operative angle between the geometrical longitudinal axis of the drill and the rotary plane of the wheel and admitting a rotation of the drill about said axis, at least one first stop means for engaging the drill and thereby preventing rotation of the drill about its axis in one direction beyond a first limiting position and at least one second stop means for engaging the drill and thereby preventing rotation of the drill about its axis in a direction opposite to said one direction beyond a second limiting position, said first and second stop means being so arranged with respect to one another and to a drill in said guiding means as to be operable to limit said rotation of said drill to a predetermined angular extent between said first and second limiting positions such that when said drill is rotated between said limiting positions and through said predetermined angular extent while a clearance surface thereof is in contact with an associated rotating grinding surface a predetermined clearance angle and a predetermined transversal cutting edge angle are both obtained.

3. Apparatus according to claim 2, wherein there is provided a number of guiding passages and guide lugs associated therewith, which guiding passages have different diameters for guiding drills of different diameters.

15. Apparatus for grinding spiral drill bits having at least one main cutting surface, a transversal cutting surface intersecting the main cutting surface and one clearance surface and a flute for each main cutting surface, comprising a rotatable wheel having a bowl-shaped conical grinding surface and having means for connecting the wheel to a driving device, a guiding element fixed in relation to the rotational axis of the wheel, a number of cylindrical guiding passages having different diameters one of which is largest and one of which is smallest provided in the guiding element at equal distances from the rotational axis of the wheel and extending in parallel thereto, for guiding drill bits of different diameters in relation to the grinding surface, guiding pins in the guiding passages adapted to engage each with one of the flutes of the drill bits in order to limit the rotational movement of the drill bits between two limiting positions corresponding to the points of engagement of said flutes and said pins, said pins being so arranged with respect to one another and to a drill bit in said guiding passage as to be operable to limit said rotation to a predetermined angular extent between said limiting positions such that when said drill is rotated between said limiting positions and through said predetermined angular extent while a clearance surface thereof is in contact with an associated rotating grinding surface a predetermined clearance angle and a predetermined transversal cutting edge angle or both obtained and an abutment united with the guiding element for determining the position of the drill bits in relation to the guiding pins.

18. Apparatus as claimed in claim 15, wherein the guiding pins are disposed diametrically opposite each other in the guiding passage and extend inwards approximately one fourth of a guiding passage diameter towards the center of the guiding passage and being each provided with two straight abutments margins extending along two different diameters of the guiding passage forming an angle of 60* with each other.

21. Apparatus as claimed in claim 15, wherein the largest guiding passage is directed towards that point of the abutment which is nearest to the grinding surface, while the smallest guiding passage is directed towards the point that is most remote therefrom, while the other guiding passages are distributed therebetween according to their diameters.