CA1249129A - Drill sharpening tool - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

A twist drill sharpening tool comprises a body housing a cylindrical rotatable grindstone of small diameter and a drill holder which can be fitted into a bore in the body so as to hold the tip of a twist drill in contact with the curved surface of the grindstone at a position which is offset from the centreline and inclined at between 10° and 12° from a diametral plane of the grindstone passing through the drill tip contact line with the grindstone. A cam on the body is engaged by a cam follower of the drill holder so as to vary the projection distance of the drill as it is turned about its own axis, carried by the holder. The bore for the drill holder may be formed in part of the body which can be moved to different positions to vary the drill tip angle.

Description

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2 BACKGROUND OF TH~ INVE~TION

4 The re-sharpening of twist drills presents many difficulties both for professional engineer and amateur 6 alike. The main problem lies in the complex shape of 7 the twist drill tip which is rarely fully understood.

9 Although a twist drill appears at a casual glance to be no more than a rod-like body with helical flutes, the 11 precise configuration is in fact rnuch more complex than 12 this; the twist drill tip, in particular, has a shape 13 which can only be apprec.iated by careful study. For 14 example, the "pointed" end of the tip is in fact a chisel edge and the generally conical "lands" on either 16 side of this are neither flat nor cylindrically curved 1~7 but should have a curving inclination from the çutting 18 edge to the trailing edge with respect to a plane ~.
19 perpendicular to the drill axis and a curvature which 20~ varies radially of the tip to approximate a conical 21 surface.

23 Various drill sharpening tools are known in the prior 24 art. In one such known tool there are provided guides opexable to grind "flats" Oll the end faces of the drill 26 by running the drill along a flat grindstone; this is 27~ largely unsatisfactory, however, since the tip end 28::: surface~s should be curved to give clearance for the tip :, , `~ ~ ; 29 face after cutting. Other known devices act to hold the drill in a required~orientation about its axis, and to : 31 sweep the tip of the drill about an axis inclined at an : : 3~ :acute angle~to the longitudinal axis of the drill whilst : : 33 passing the tip end surEace of the drill across a flat :
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1 or curved grindstone surface. The fundamental 2 disadvantage of this arrangement lies in the fact that

3 the two "lands" of the drill tip surface are separated

4 by a chisel edge and are effectively independent. By grinding the two "lands" separately the problem arises 6 of longitudinally aligning the drill sufficiently 7 accurately for both ~lands" to be ground symmetrically 8 with respect to the longitudinal axis of the drill.
Unless exactly the same amount of material is removed 11 from each land then the offset of the cutting edge from 12 its intended position will be different for each land.

16 It is a primary object o the present invention to 17 pxovide a drill grinding tool which is capable of 18 accurately grinding both lands of a drill tip to the 19 same shape and configuration.
21 It is another object of the prese~t invention to provide 22 a drill grinding tool which is simple to operate and 23 requires no skill in setting up It is a further object of the invention to provide a 26 drill grinding tool in which drill grinding is effected 27 by turning the drill about its own longitudinal axis.

29 Yet anothe~ object of the invention is to provide a drill grinding tool in which the shape of the tip ground 31 on the drill is detérmined by cams which control the 32 depth of cu-t of the grindstone against the drill tip.

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3: ~9 1 Yet another object of the invention is to provide a 2 drill grinding tool which is simple, robust and 3 economical and which is able to regrind drills of any 4 size withini a given range withou-t requiring any adaptation or modification.

9 The present invention thus provides a twist drlll sharpening tool comprising:
11 A structure supporting a rotatable grindstone 12 having a cylindrically curved surface, said structure 13 including a body having a body portion extending 14 transversely of the axis of said cylindrically curved surface of said g.rindstone, 16 - a first guide surface on one of said body and a 17 member carried thereby, 18 - a twist drill holder including retainer means for 19 retaining a twist drill firmly against relative movement with respect to said holder both parallel to the axis of 21 said drill and around the axis of said drill, 22 : - a second guide surfaoe on said drill holder for 23 co-operative engagement with said first guide surface 24 whereby to control the advance of said drill in a direction parallel to its own axis towaxds said 26 grindstone in dependence only on the relative angular 27 orientation of said drill about its axis with respect to 28 said body of said tool, : 29 - a third guide surface on said body and, - a fourth guide surface on said drill holder, said 31 fourth guide surface co-operatively engaging said third : 32 guide surface whereby to retain said drill holder and ~ 33 said twist drill carried thereby with its axi5 in a :~ ~
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1 predetermined angular orientation with respect to the 2 axis of said grindstone whilst allowing said drill 3 holder and said twist drill carried t:hereby to turn 4 about said longitudinal axis of said twist drill and to be displaced parallel to said longitudinal axis of said 6 twist drill by said co-operative engagement of said 7 first and second guide surfaces whereby -to determine the 8 shape of the tip ground on said twist drill, said g co-operative engagement of said third and fourth guide surfaces locating said drill holder such that a drill 11 held thereby lies in a plane inclined at a predetermined 12 angle with respect to a plane perpendicular to the axis 13 of the cylindrical surface of said grindstone and is 14 retained with the line of contact between the drill tip and the cylindrical surface of the grindstone extending 16 generally parallel to the axis of said cylindrical 17 surface and off-set from a diametral plane of said 18 grindstone parallel to the axis of said drill, whereby 19 sharpening of the drill is effected solely by rotation of the said drill holder about the axis of the drill 21 held thereby.

23 The present invention also provides a method of 24 sharpening a twist drill in which the drill is turned solely about its longitudinal axis, with its tip in 26 contact with a grindstone. ~y contrast with known 27 methods of drill sharpening the method of the present 28 invention and the drlll sharpening tool of the present 29 invention each enable the two "lands" of the drill tip to be ground without changing the position of the drill 31 in a drill holder, consequently ensuring that the two ,

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1 "lands" of the drill tip surface are in axial register 2 with one another and both are entirely symmetrical.

4 Various other features and advantages of the invention will become apparent from a study of the following

6 description with reference to the accompanying drawings,

7 which is given purely by way of non-limitative example.

11 Figure 1 is a perspective view of a drill tip 12 illustrating the various faces and the way in which a 13 drill has to be sharpened;
14 Figure 2 is an end view of the drill of Figure 1;
Pigure 3 is a front view of a first embodiment of 16 the invention;
17 Figure 4 is a perspective view from the front and : 18 side o~ a second embodiment of the invention;
19~ Figure S is a partly sectioned front view taken on : : 20 the line V-V of Figure 4;
~: 21 Figure 6 is a partly:sectioned exploded view taken :~ 22 on the line V1-V1 of Figure 4 of one form of drill 23 holder for the tool of the present invention;
~ ~ 24 Figure 7 is a perspective view of a component of ; : 25 the embodiment of Figures 4,5 and 6;
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2~ Figure & is a perspective view of a further 27: embodiment of the invention;
28 ~ ~: Figure 9 is a section taken on the line IX-IX of 29 Figure 8;
: Figure 10 is a sectional view of a tool holder 31 adapted for gripping small drilIs; and 32 Figure 11 is a perspective view of a collett insert 33 for the tool holder illustrated in Figure 10.

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DESCRIPTION OF THE PREFERRED EMBODIMENTS

3 Referring first to Figures 1 and 2, t:he shape of a twist 4 driil is lllustrated. This comprises, as known, a S central web generally indicated 11 which constitutes the 6 central portion of a twist drill body generally 7 indicated 12 having a cylindrical outer surface 13 in

8 which there are formed two deep helically extending

9 channels generally indicated 14, 15. At its tip the drill is formed with a generally conical end surface 16 11 separated into two "lands" 16a, 16b by a crest or ridge 12 17 in the form of a chisel edge which intersects the 13 longitudinal central axis of the drill body.

Each "land" is identical to the other and consequently.
16 only the land 16a will be described in detail since this 17 is the most visible in Figure 1. The twist drill is, in 18 use, rotated about its longitudinal central axis in an 19 anti-clockwise direction as viewed in Figure 2 so that the leading edge of the land 16a is the edge between 21 this land and the spiral flute 15, which has been 22 identified with the reference numeral 20. The trailing 23 edge 21 of the land 16a meets with the spiral flute 14.
24 As can be seen the leading edge 20 is substantially straight between the point where it meets the chisel 26 edge or ridge 17 and the point where it meets the outer 27 circumference 13 of the drill body. This edge continues 28 as an unbroken line from the point of intersection 29 between the chisel edge or tip 17 and the leading edge 20 of the land 16a as a curved trailing edge 22 of the 31 land 16b. Likewise~ the curved trailing edge of the 32 land 16a extends from the cylindrical surface 13 of the 33 drill in a continuous curve to the point where it , .. . ..
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1 intersects the line of the drill tip chisel edge 17,2 from which point the edge continues, as a straight line, 3 as the leading edge of the land 16b. The two straight 4 leading edges 20, 23 constitute the cutting edges of the drill itself, and these are continued as the helical 6 leading edges of the cylindrical surface 13 where this 7 cylindrical surface meets the flutes l4, 15. A raised 8 "ribboni' of this surface, generally indicated 24 ensures 9 that the cylindrical surface 13 is in fact sligh~ly recessed from the hole being formed by the drill to 11 minimise frictional contact.

13 The precise form of the drill tip is extremely important 14 in relation to the cutting operation to be performed by the drill. In particular the length of the chisel edge 16 17 in relation to the overall diameter of the drill, 17 which in turn determines the lateral separation of the 18 cutting edges 20,23 (transverse their length~, the 19 inclination of the cutting:edges 20, 23 with respect to a transverse diametral plane of th~ drill tip, 21 identified by the circular plane generally indicated 25 22 in Figure 1, and the "-Fall" or inclination of the lands 23 16a, 16b between the leading and trailing edges with ~
24 respect to a plane orthogonal to the a~is of the drill are quite critical. The "fall" is particularly 26 important since it ensures the ability of the cutting 27 edge to pass freely over the blind end of a hole being 28 : drilled without undue frictional contact between thP
29 dxill tip and the hole, thereby ensuring that the cutting edges alone contact the work and this can be 31 seen as a separation between the two broken line circles 32 26, 27 in Figure 1. In:fact, the broken line circle 26 33 represents a plane perpendicular:to the axis of the ~. ~
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1 drill and passing through the point of intersection of 2 the leading edge 20 with the cylindrical surface 13, the 3 so-called "shoulder" o~ the cutting edge, and the circle 4 27 represents the corresponding intersection between the trailing edge of the land 16a and the surface 13, this 6 "fall" is identified by the axial distance "h" in Figure 7 1.
g g Although drill tips axe accurately formed when new, continuous use eventually blunts the cutting edges and 11 the drill has to be sharpened. This is a highly skilled 12 operation to perform manually since it requires a close 13 knowledge of all the required parameters of the drill 14 and sufficient experience to know how to hold the drill at the required angle to avoid grinding the lands flat, 16 to preserve the chisel edge ~7 separating the two lands, 17 to maintain this at the correct inclination with respect 18 to the cutting edges 20,23 and at the same time to 19 preserve the inclination of the "~all" with respect to the perpendicular planes 26:,27.
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22 All these things can be achieved automatically using the 23 drill:sharpening tool of the present invention without 24 requiring any skill and without being dependent on any particular drill size. The two embodiments ilIustrated 26 in Figures 3, 4 and 5 differ only in the mechanism for 27 setting a drill in the required preliminary position, 28 and components which fulfill the same or similar : 29 functions in the two~embodiments will be referred to with the same re~erence numerals.

: 32 The tool is formed as two separate cooperating parts, 33 comprising a drill holder 28 and a grindstone holder 29.
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1 The latter comprises a body 30 generally composed of two 2 interpenetrating cylindrical body portions 31, 32 each 3 of which has a respective cylindrical cavity 33, 34 4 which communicate with each other. The cylindrical cavity 34 in the body portion 32 is enlarged by a 6 lateral trapezoidal section chamber 35 on the side 7 nearest the cylindrical body portion 31.

9 One end of the cylindrical bore 34 carries a bearing (not shown) within which runs a spindle 36 carrying a 11 cylindrical grindstone 37. The bearing (not shown) 12 incorporates suitable dust and grit seals for the 13 purpose of retaining any grinding dross within the 14 chamber constituted by the bore 34 and trapezoidal extension 35. The spindle 36 may be fitted with a drive 16 pulley for connection to an electric motor, or can be 17 gripped by the chuck of a conventional electrical pistol 18 drill of the widely available and well known type, not 19 ~hown in the drawings.
21 The drill holder 28 has a generally cylindrical body 3 22 with a cylindrical bore 39 extending axially there-23 through and a radial flange 40 at one end. The 24 cylindrical outer periphery of the flange 40 is threaded and receives the internally threaded skirt 41 of a cap 26 42 having a central axial bore 43 which passes through 27 the body of the cap 42~and through a central axial boss 28 44 formed on the inside face of the cap. The bore 43 29 has a conically tapered end portion 45 where it passes through the boss 44. The diameter of the boss 44 is 31 such that it forms a sliding fit within a laterally 32 enlarged end portion 46 of the bore 39 within the 33 cylindrical body 38 of the tool holder. The opposite , , , . , :
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1 end of the bore 39 from the laterally enlarged port.ion 2 46 also ha~ a conically tapered end portion 47, both of 3 these tapers having a cone angle of 20, that is an 4 angle of lnclination o:E 20 between the axis and a generatrix of the conical surface. At the upper end of 6 the holder and passing through the enlarged portion 46 7 are two diametrically opposed axial grooves in the wall 8 of the hore 39, identified with the reference numeral 9 51. These recesses or grooves receive respective diametrically opposed projections of a resilient insert 11 shown separately in Figure 6, and comprising a 12 cylindrical body 48 having conically tapered ends 49, 50 13 with a cone angle of 10 and of a length such as to fit 14 closely between the conically tapered parts 47,45 of the bore 39 and the bore 43 in the cap 42 respectively.
16 Each of the conically tapered end portions 49, 50 of the 17 insert 48 has a plurality of axial slots 52, say four or 18 five, so that the conically tapexed end portions 49, 50 19 can be resiliently closed in the manner of a drill chuck,:by relative approaching movement of the body 38 21 and the cap 42 effected by screwing the cap 42 with 22 respect to the body 38 on the screw threads of the 23 flange 40 and cooperating skirt 4~. The cylindrical 24 body 48 is normally loosely fitted in the bore 39 and a drill, such as the drill 53 illustrated in Figure 4 can 26 be positioned within it by introducing it into the 27 opening 43 in the cap and pushing ik through the bore 39 28 in the body 38.: Then by~relatively turning the cap 42 29 and the body 38 a light pressure can be applied to the dxill to retain it in position whilst the body 38 of the 31 drill holder is fitted into the bore 33 in the 32 cylindrical body portion 30 of the grindstone holder 33 part of the tool.

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. , , . :.. ' 1 The drill holder 28 has one further component of 2 importance, namely a locating pxojection 54 which 3 extends ax:ially from the flange 40 and lies closely 4 alongside the outer cylindrical surface of the body portion 38. The locating projection 54 contacts the 6 annular cylindrical end surface yenerally indicated 55 7 of the cylindrical portion 31 of the grindstone holder 8 30. This annular end surface has two diametrically 9 opposed "lands" 56, 57 separated by two, likewise diametrically opposedr recesses 58, 59 which, as can be 11 seen in Figure 4, are not perpendicular to the axis of 12 the cylindrical portion 31 but are inclined at an angle 13 to such perpendicular plane as ilIustrated by the broken 14 line 70 of Figure 4.
16 This angle ~ determines the "fall" of the lands as 17 the drill -tip is turned in contact with the cylindrical 18 surface of the grindstone, for which purpose the drill 19 holder 28 is introduced into the cylindrical bore 33 in the body portion 30 of the tool.

22 . Obviously, the relative angular orientation of the drill ~3 53 and the drill ho~der 28 is critical to the proper 24 operation of the tool and this is achieved by means of a settling device generally indicated 60 in the embod-26 iments of Figures 3,~ and 5 28 ~ The drill setting device 60 in the embodiment of Figure 29 3 is simply constitutéd by a cylindrical bolt 61 having an enlarged head 62 and surrounded by a helical spring 31 63 within a bore 64 in a lateral projection 65 of the 32 tool body. This projection 65 has an L-shape slot 66 33 throùgh which projects a pin 67 secured to the enlarged :

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1 head 62 of the bolt 61 and carrying a knurled finger 2 grip 68~ The coil spring 63 urges the bolt 61 to the 3 right as viewed in Figure 3 and the :Eorce exerted by 4 this spring can be overcome by displ,acing the finger grip 6~ to -the left as viewed in Figure 3 and engaging ~ it in the foot of the L-shape slot 65, in which position 7 the bolt 61 is advanced as shown in Figure 3 so that its 8 end face 69 forms a reference surface against which a 9 cutting edge of the drill tip can be engaged to determine the angular orientation of the drill 53 with 11 respect to the tool body 30. If the drill holder 28 is 12 then turned to a reference orientation, for examplet 13 identified by cooperating marks on the body and the 14 drill holder the tool will be set up in the required position.

17 The embodiment of Figures4 and 5 is an improvement on 18 this arrangement in that the projection 65, conveniently 19 formed as an insert, has a generally U-shape slot 71 having two circumferentially extending arms 72, 73 and 21 ;within the bore 64 of the~projection 65 is housed a 22 shaped bolt 61 having a notch 74 at the inner end, an 23 :inclined shoulder 75 and a recessed cam face 76 which 24 engages a cam follower 77 housed in a bore 78 extending:
axially of the cylindri~al portion 30. The cam follower 26 77 has an upper free end 79 which can project from the 27 annular end face of the tool body coincident with one of 28 the recesses 59 and closely adjacent one end of this 29:~ recess.
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31 As:will be seen from Figure 4 the circumferential arm 73 32 of the slot 71~ is:longer than the arm 72 so that when 33 the pin 67 is engaged therein the adjacent end of the ,, :

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~, ~2~ l2~3 l cam follower 77 is lodged in the recess constituting the 2 cam face 76. When the pin 67 is displaced circum-3 ferentially to engage -the axial part of the slot 71, and 4 whilst it is in the arm 72, the bolt 73 is turned so that the cam follower rises up the cam face 76 and 6 engages on the cylindrically curved surface of the bolt 7 73 thereby causing the free end 79 of the cam follower 8 77 to project from the recess 59 in the annular encl face 9 of the cylindrical portion 31 of the tool body 30.
Adjacent this point in the recess 59 is a notch 50 11 which, together with the projecting end face of the cam 12 follower 79,constitutes a seat for the locating 13 projection 54 of the tool holder 28. This then 14 automatically defines the reference position of the tool holder 28 for setting the drill in its re~uired angular 16 orientation. The shaped end 74 of the bolt 73, together 17 with the inclined shoulder 75, makes close contact with 18 the end of the drill, being largely complementary in 19 shape. Once -the drill has been set in its required angular orientation ~he bolt 73 is withdrawn, the cam 21 follower 77 is lowered so that the end face 79 now 22 becomes flush with the recessed surface 59 and the 23 sharpening operation can proceed as before by rotating 24 the spindle 36 and turning the drill holder 28 until the tip of the drill has been ground away sufficiently for 26 the locating member 54 to be in contact with the annular 27 end face 55 of the cylindrical portion 31 of the body 30 28 over the whole of its circumferential travel.

The dimensions of the body 48 of the insert illustrated 31 in Figure 6 are such that the resilient fingers formed 32 between the slots 52 can be displaced radially between 33 a position, when radially compressed to the maximum ; ; - 14 -, . . .
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1 extent, such as to grip a drill of about one-quarter 2 inch to a position where, at the maximum or almost to 3 the maximum relaxed state, a drill of about half an inch 4 diameter can be acco~modated. To accommodate smaller dxills an insert having a thicker wall and, perhaps, 6 larger slots 52 ~larger, that is, in the circumferential 7 direction) enabling the fingers to be moved to a smaller 8 radius gripping position could be employed. In order to 9 be able to sharpen extremely fine drills a secondaxy insert, capable of being fitted into the insert 11 illustrated in Figure 6, and having a greater axial 12 length such as to support a very fine drill closer to 13 its tip and nearer to the grindstone 37 could be 14 provided.
16 In a further modification, adapted to be able to 17 accommodate twist drills having different cutting angles 18 (that is the angle between the drill axis and the ~
19 cutting edge measured through a diametral plane of the drill) could be provided. For this purpose the spindle 21 36 must be releasably held in the bearing in the body of 22 the stone holder 30~so that grindstones 37 ha~ing a 23 different ~orm can be interchangeably fitted. Thus,~for 24 example, instead of~having a right cylindrical surface, a grindstone havinq a conical surface can be fitted to 26 the tool so that, together with the combination of 27 angles~which can~be seen fr~om Figurés 3, 4 and 5, 28 enables the use of different drill~grinding angles. A
9 set of stones 37 havin~ cone angles differing by, say, five degrees from one another, is envisaged.

32 The embodiment of Figures 8, 9 and 10 also allows 33 adjustments to be~made to change the angle at which the ~ - 15 -:

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l drill tip is ground, but in this latter embodiment the 2 change can be efPected with great ease and simplicity.

4 Referring first to Figures 8 and 9 the tool shown comprises a solid block body generally indicated 101 6 having an axial hole 102 therein for receiving a 7 cylindrical grindstone (not illustrated) mounted on a 8 spindle carried by bearings 103 supported on a back wall 9 104 oP the body 101. The spindle is the output shaft of an electric motor 100 also carried by the back wall 104.

12 The body 101 is formed in two parts, namely a main body 13 part 133 and a drill holder guide part 131. A guide 14 hole 105 which as in the previous embodiment is inclined in two planes, provides guidance and location for a 16 drill holder (not shown) which may be substantially the 17 same as that described in the earlier embodiments or as 18 shown in Figures 10 and 11 and described below. The 19 guide hole 105 is formed in a drill holder guide part 131 of the body~ which is pivotally mounted at 132 to 21 the main body part 133. The drill holder guide part 131 22 of the body is located within an elongate opening 134 in 23 the main body part 133 which:is larger than the outer 24 diameter of the drill holder guide part 131 allowing it to rock about the pivot 132 between two terminal 26 positions defined by contact oP the drill holder guide 27 part 131 with:opposite faces of the hole 134. The side 28 wall~of the main body portlon 133 has an aperture 29 ~ through which p:asses a locating pin 135 which can engage in one of a set oP corresponding holes (not shown) in 31 the guide holder body part 131 to locate it at a 32 selected angle.: These are marked on the upper Pace with 33 guide lines indicated with the drill tip anglè to be ,~
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1 ground~ In Figure 6 the lines are marked 90~, 118 and 2 130.

4 ~he upper face 106 of the guide holder body part 131 has guide surfaces 109 in the form of a single raised face 6 cam for determining the longitudinal advance of the 7 drill upon rotation of a drill holder such as that shown 8 in Figures 10 and 11 holding the drill in alignment with 9 the inclined guide hole 105.
11 In the horizontal upper face 108 of the main body par 12 133 are formed two holes 110, 111 housing respective 13 V-blocks 112 located in a predetermined angular 14 orientation by means of a flat on at least one face, and secured in position by means of screws 114 extending up 16 from the bottom f~ce of the body and which serve to 17 adjust the height of the V-blocks 112 in relation to the ~: 18 horizontal face 108 of the main body part 133. As the 19 stone wears the screw:114 can be turned to lower the V
block and increase the set length of the drill. The two 21 ~holes 110, 111 are identical to one another except for 22 diametral size, the latter being larger to accommodate:
23 d~ills of a larger:diameter. Hereinafter only~the~hole 24 110 will be described in further detail, it being Z5 ` understood that the detaiIs of the hole 111 will be :26 identical.
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28 The two holes 110, 111 are formed at the botto~ of an 29 oval recess ~11;3;the functi~on of~which is to provide two opposite shoulders~118 aga1nst which engage flats 119 in 31 the drill holder body to determine the angular 32 orientation thereof when it is fitted in the recess.
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:. ' . :': -1 It can be seen that in relation to the earlier 2 embodimen-ts described, the er~odiment of Figures 8 and 9 3 comprises a regular and easily formed body in place of 4 the shaped body previously provided and the complex setting device has been very much simplified. Drill 6 setting in the holder wlll be described in more detail 7 below.
9 Referring now to Figures 10 and 11, there is shown a drill holder which can be used even for very small 11 drills, comprising a sleeve 120 having a plain bore 121 12 into which is fitted a control body 122 which has an 13 internal bore passing right through and comprising three 14 portions a first portion 123 which is threaded, a second portion 129 which is tapered and a plain bore third 16 portion 128 which opens into an end face l30 of the 17 control body 122. The threaded shank of a gripper 18 element 124 is screwed into the threaded portion 123 of 19 the bore in the control body 122, and this gripper ele~ent 124 has a tapered end 125 matching that of the 21 tapered portion 129 of the bore. The end of the gripper 22 element remote from the tapered end 125 comprises a 23 conically outwardly flared or tapered block 126 having a 24 plurality of elongate slots 127 which extend from the flared end 126 to about mid-way along its length. The 26 ~lared end 126 has:six flat faces 116 so positioned that 27 each is bisected by a:longitudinal slot 127. A second 28 ~set: of slots 139 extends from the tapered end 125 to a 29 point closely adjacent the ends of the slots 127. As the control body 122 is turned in relation to the sleeve 31 120 it draws the gripper body 124 axially by the screw 32 threaded connection. The flared end 126 is held from 33 turning by the flats 116 and is caused to flex inwardly, , ,' ',:,, :,'~:
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1 such flexure being allowed by the slots 127, to grip a 2 drill positioned thereln. At the SaMe time, contact 3 between the tapered end 125 of the gripper element 124 4 and the correspondingly tapered intermediate portion 129 of the bore in the control body 122 causes the tapered 6 end to flex inwardly closing the slots 139 and gripping 7 the shank of a drill in the holder at a point axially 8 spaced from the flared end 126 so that no rocking of the 9 drill with respect to the hold~r can take place.
11 This embodiment of the invention is used as follows: -12 First a drill is fitted into the holder as described 13 above and the control body 122 turned with respect to 14 the sleeve 120 until the drill is lightly gripped. Then the holder is fitted into the oral recess 113 with the ; 16 flats 119 on the sleeve 120 in contact with the side 17 walls 118 of the recess, which define abutment shoulders 18 to determine the orientation of the holder. The drill, 19 only being lightly gripped, can be pushed into the hole 110 or 111 as appropriate until its tip contac~s the 21 V-block 112. Then by turning the drill one way or the 22 other a position of maximum~penetration can be felt 23 defining the required orientations of the drill. The 24 control body is then turned to firmly clamp the drill, the holder removed from the recess 113 and fitted to the ~6 bore 105. The~stone is set in motion and the drill 27 holder turned with its guide pegs 115, 117 successively 28 ~ contacting the cam face 109 to control the axial ` 29 position of the drill as it is turned. The tip is ground by contact with the stone until no more metal i5 31 worn away and is then sharp. The shape of the cam 109 32 is chosen with a convex curvature such that the required 33 curvature of the drill tip faces 16a, 16b is obtained.

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, 1 The shape of this curve is the same for drills of all 2 sizes and i5 unchanged regardless of the drill tip angle 3 so no change to the cam profile is required when the 4 drill holder part 131 of the body is moved to a different position to change the drill tip angle.

7 In another embodiment (not shown) provision is made for 8 sharpening masonry drills having a hardened tungsten 9 carbide or otller hard insert as well as -for steel twist drills. ~his adaptation, based on the embodiment of 11 Figures 8 and 9, includes a different tool holder which, 12 with the drill holder guide part 131 moved to a special 13 position, lower than the 130 position illustrated in 14 Figure 8, enables the tip of the drill to be ground against the flat end face of the stone instead of the 16 curved surface of the stone which is used for twist 17 drills. In this arrangement it is unnecessary to turn 18 the drill about its own axis since the sharpening 19 process involves grinding flats at an angle on the end face of the drill so the drill is merely adv~nced until 21 it contacts the end ace of the stone and then turned 22 through 180 to grind~ the other side of the tip.

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Claims (16)

What is claimed is:

1. A twist drill sharpening tool comprising:
- a structure supporting a rotatable grindstone having a cylindrically curved surface, said structure including a body having a body portion extending transversely of the axis of said cylindrically curved surface of said grindstone, - a first fixed guide surface on one of said body and a member carried thereby, - a twist drill holder having a longitudinal axis and including retainer means for retaining a twist drill firmly with its axis parallel to said twist drill holder longitudinal axis against relative movement with respect to said holder both parallel to the axis of said drill and around the axis of said drill, - drill position setting means for determining the angular orientation of a twist drill in said twist drill holder whereby to set a twist drill with its tip projecting a predetermined distance from said twist drill holder and in a predetermined angular orientation about its longitudinal axis with respect to s id twist drill holder, - a second fixed guide surface on said drill holder for cooperative engagement with said first fixed guide surface whereby to control the advance of said drill in a direction parallel to its own axis towards said grindstone in dependence only on the relative angular orientation of said twist drill holder about its axis with respect to said body of said tool, - a third fixed guide surface on said body and, - a fourth fixed guide surface on said drill holder, said fourth fixed guide surface cooperatively engaging said third fixed guide surface whereby to retain said drill holder and said twist drill carried thereby with its axis in a predetermined angular orientation with respect to the axis of said grindstone and non-adjustably fixed against turning movement about any axis transverse said twist drill holder longitudinal axis whilst allowing said drill holder and said twist drill carried thereby to turn about said longitudinal axis of said twist drill and to be displaced parallel to said longitudinal axis of said twist drill by said cooperative engagement of said first and second fixed guide surfaces whereby to determine the shape of the tip ground on said twist drill, said cooperative engagement of said third and fourth fixed guide surfaces locating said drill holder such that a drill held thereby lies in a plane inclined at a predetermined angle with respect to a plane perpendicular to the axis of the cylindrical surface of said grindstone and is retained with the line of contact between the cutting edges of the drill tip and the cylindrical surface of the grindstone extending generally parallel to the axis of said cylindrical surface and off-set by a predetermined non-adjustable distance from a diametral plane of said grindstone parallel to the axis of said drill, whereby sharpening of the drill is effected solely by rotation of the said drill holder about the axis of the drill held thereby.

2. The twist drill sharpening tool of Claim 1, wherein said body portion projects from said body and said first guide surface is formed on an end face of said projecting portion.

3. The drill sharpening tool of Claim 2, wherein said third guide surface is a generally cylindrical bore in said body portion for receiving said drill holder, and said first guide surface is formed on an end face of said body portion and comprises at least one raised cam face for displacing the cooperating said second guide surface axially of said bore as said drill holder is turned about the bore axis.

4. The drill sharpening tool of Claim 3, wherein said cam surface has a notch defining a shoulder against which said second guide surface can be engaged to set said drill holder in a predetermined angular orientation about the drill axis with respect to said tool body.

5. The drill sharpening tool of Claim 1, wherein said tool body has a drill tip abutment means against which a given part of a twist drill tip can be located to set said drill in a predetermined angular orientation about its own longitudinal axis with respect to the tool body.

6. The drill sharpening tool of Claim 1, wherein said twist drill retaining means on said drill holder include releasable clamping means.

7. The drill sharpening tool of Claim 1, wherein there are provided means for setting the angular orientation of said drill about its own axis with respect to said drill holder of said tool, in which said means for setting said angular orientation of said drill comprise a drill setting member having two generally plane faces inclined to one another and meeting along a line perpendicular to the axis of said drill held by said holder with its tip in contact with said two plane faces simultaneously.

8. The drill sharpening tool of Claim 1, wherein said body is formed in two parts comprising a first part having means for supporting said grindstone for rotation about its axis and a second part having means for receiving and supporting said tool holder such that said tip of said drill is in contact with said grindstone, said second part being angularly displaceable with respect to said first part about an axis orthogonal to the axis of said grindstone between at least two positions whereby to vary said drill tip angle ground in use of said tool.

9. The drill sharpening tool of claim 8, wherein said second part of said tool body is displaceable between three predetermined positions about said axis whereby to adapt said tool for grinding drills having one of three different drill tip angles.

10. The drill sharpening tool of Claim 1, wherein there are provided means for varying the length of projection of said drill from said drill holder whereby to compensate for wear on said grindstone after a period of use.

11. The drill sharpening tool of Claim 1, wherein said drill holder comprises a sleeve having an axial bore with an outwardly flared mouth portion at one end thereof, - a clamping collet member having a correspondingly outwardly flared end portion, - means defining a hollow axial bore in said clamping collet member, and - means defining a plurality of diametral slots extending part way along said hollow axial bore in said clamping collet member, and - a screw control member having a screw threaded bore into which the other end of said clamping collet can be threadedly engaged and which fits into the other end of said bore in said sleeve.

12. The drill sharpening tool of Claim 11, wherein said bore in said screw control member has a tapered portion adjacent its end opposite that into which said clamping collet screws, and said clamping collet has a tapered outer portion which cooperatively engages said tapered portion in said screw control member such that as said screw control member and said clamping collet are screwed together said sleeve abuts said shoulder and said clamping collet is drawn into it so as to be compressed radially by said tapered portions at each end thereof.

13. The drill sharpening tool of Claim 1, wherein said grindstone is mounted on a spindle turnable in bearings carried by said tool body and projecting therefrom for attachment to a coupling of drive means such as a pistol drill.

14. The drill sharpening tool of Claim 1, wherein said grindstone is mounted on a spindle turnable in bearings carried by said tool body and connected to a drive motor also carried by or attached to said tool body.

15. A twist drill sharpener comprising a rotary grinding wheel having a cylindrically curved grinding surface and a grinding wheel axis, - grinding wheel support means rotatably supporting said rotary grinding wheel for rotation about said grinding wheel axis, - a drill sharpener body housing said grinding wheel support means, - drill holder means having a longitudinal axis, a first end and means for gripping a twist drill and holding it fixedly with the drill axis parallel to said longitudinal axis of said drill holder means, - at least one cam guide surface on said drill holder means, - twist drill position setting means for determining both the relative angular orientation of a twist drill with respect to said drill holder means and the distance by which the tip of a twist drill projects from said first end of said drill holder means, - drill holder receiving means for receiving said drill holder means with said first end thereof facing towards said rotary grinding wheel, - an internal fixed guide surface of said drill holder receiving means guiding said drill holder means to rotate about its own longitudinal axis, - means pivotally mounting said drill holder receiving means in said drill sharpener body for turning movement about an axis orthogonally intersecting said grinding wheel axis, - drill tip angle setting means for fixing said drill holder receiving means in a selected angular orientation about said axis orthogonally intersecting said grinding wheel axis, - fixed cam guide surfaces on said drill holder receiving means engageable by said at least one cam guide surface on said drill holder means to cause said drill holder means to reciprocate longitudinally a predetermined axial distance as it is turned about its longitudinal axis, said internal fixed guide surface cooperating with said drill holder means to position a twist drill held by said drill holder means in a position determined by said twist drill position setting means and said drill tip angle setting means, such that its axis lies at an angle to said grinding wheel axis determined by the required drill tip angle to be ground, and further lies at an angle to the diametral axial plane of said grinding wheel passing through the line of contact between said drill and said grinding wheel whereby upon turning said drill holder means about its axis guided by said internal fixed guide surface of said drill holder receiving means the tip of said twist drill held thereby is sharpened and ground with a chisel edge and a heel clearance while being retained with its axis fixed in relation to said grinding wheel axis.

16. A twist drill sharpening tool comprising:
- a housing, - a grindstone having an axis and a cylindrical outer surface, - means for rotatably mounting said grindstone to said housing around said grindstone axis, - said housing having a body which extends transversely outwardly from the axis of the grindstone, means for fixing said body against movement with respect to said housing during a sharpening operation, said body having a cylindrical throughbore, said body throughbore having a fixed axis during said sharpening operation which is inclined at a predetermined angle with respect to a plane perpendicular to the grindstone axis and which is also parallel but spaced from a diametral plane of the grindstone axis, - a drill holder having an axis and an outer cylindrical surface with substantially the same diameter as said body throughbore so that said tool holder is axially slidably and rotatably received in said body throughbore but constrained against transverse movement with respect to said body, - said drill holder having a coaxial throughbore, - means contained within the drill holder throughbore for releasably holding a twist drill against both rotatable and axial movement with respect to said tool holder and so that the twist drill protrudes outwardly from an end of the drill holder adjacent the grindstone, - a first cam surface on said body, - a second cam surface on said drill holder which cooperates with said first cam surface to axially displace said drill holder upon rotation of said drill holder and in an amount dependent upon the angular rotational position of said drill holder, - wherein sharpening of a drill held by said drill holder is completely effected solely by rotation of said drill holder in said body throughbore coupled with the axial displacement of said drill holder caused by coaction between said cam surfaces but without transverse movement of said drill holder with respect to the axis of the grindstone.