Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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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
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19 perpendicular to the drill axis and a curvature which
20~ varies radially of the tip to approximate a conical
21 surface.
22
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
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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.
13
14 OBJECTS OF THE INVENTION
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
24
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.
28
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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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.
7 SUMMARY OF THE INVENTION
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.
22
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
32
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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.
9 BRIEF DESCRIPTION OF THE DRAWINGS
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;
:
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.
14
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.
1 2
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.
31
: 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.
21
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
27
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.
16
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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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.
29
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
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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
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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.
1 1
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.
27 : ~ :
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.
- 19 -
::
~,
.....
,
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.
23
24
2G
27
28
2~
31
32
33
- 20 -
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~: :
' : :
