US3456392A - Twist drill grinding machines - Google Patents

Description

y 22, 1959 v J. M. BRAMHALL 3,456,392

' TWIST DRILL GRINDING MACHINES Filed Aug. 30. 1966 4 Sheets-Sheet l INVENT R 30H N\\C.\\EL. Rnn-mqLL BY can ATTORNEYS July 22, 1969 Filed Aug. 30. 1966 J. M. BRAMHALL TWIST DRILL GRINDING MACHINES 4 Sheets-Sheet 2 Fla. 2 I

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Hm MA ATTQRNEY y 2, 1969 J. M. BRAMHALL 3,456,392

TWIST DRILL GRINDING MACHINES Filed Aug. 30. 1968 4 Sheets-Sheet 5 \NvEN-roR Ann: M \cunel. Bahia HQLL ATTORNEY! y 1969 J. M. BRAMHALL. 3,456,392

TWIST DRILL GRINDING MACHINES Filed Aug. 30. 1966 4 Sheets-Sheet 4 Mum NM'QQ'EZI QEMHM BY ML (MA MAL ATTORNEY United States ,Patent Office 3,456,392 Patented July 22, 1969 3,456,392 TWIST DRILL GRINDING MACHINES John Michael Bramhall, Grindelford, England, assignor to The Sheflield Twist Drill & Steel Co. Limited Filed Aug. 30, 1966, Ser. No. 576,041 Int. Cl. B24b 19/02 US. Cl. 51-101 3 Claims ABSTRACT OF THE DISCLOSURE This invention relates to a machine for grinding twist drills and has for its main object to provide a machine for grinding each flank of a centre point, split point or crankshaft drill in a single operation.

According to the invention the machine comprises a supporting base, a grinding wheel assembly mounted on said base, a drill holder unit mounted on said base for moving a drill to be ground into engagement with the grinding wheel, a template and follower associated with said drill holder unit for controlling the movements of the drill holder to correctly position the point of the drill relative to the grinding wheel during the grinding of the drill.

In order that the invention may be more clearly understood one particular embodiment thereof will now be described, by way of example, with reference to the accompanying drawings in which:

FIGURE 1 is a plan view of the machine according to the invention,

FIGURE 2 is a side elevation thereof,

FIGURE 3 is a front elevation of the machine with parts removed for the sake of clearer illustration.

FIGURES 4 and 5 are a top plan and side elevation respectively of the drill holder shown on an enlarged scale,

FIGURE 6 is a side elevation of a detail,

FIGURE 7 is a plan view of a grinding wheel dressing device for use in conjunction with the machine, and

FIGURE 8 is a plan view of the tip or point of a centre point drill on an enlarged scale.

Referring to these drawings the machine is mounted on a supporting base or housing A and comprises a grinding wheel assembly indicated generally at B; a drill holder unit, indicated generally at C; and a follower unit indicated generally at D.

The drill holder unit C comprises an arm 1 rotatably mounted on a shaft 2 which is slidably mounted at its ends in suitable Support bearings 6 and 7, whereby the unit can be swung as a whole angularly about the axis of shaft 2 in an are indicated by the chain dotted line in FIGURE 2 and moved laterally as indicated by the double arrow in FIGURES l and 3. The drill holder unit C is retained in its inward or operative position (as illustrated in the drawings) by means of a weight (not shown) attached to one end of and suspended from a cable 3 which passes over a guide pulley 4 and is secured at its other end to said drill holder unit. The drill holder unit can be swung into its outward or inoperative position by means of a handle 1a and can be retained in said outward or inoperative position by means of a retaining catch 5a, 5b.

The shaft 2, and consequently the drill holder unit as a whole, is laterally or axially adjustable by rotation of a hand wheel 8, which is in screw threaded engagement with the shaft 2 in known manner, and such lateral or axial adjustment is limited by an axially adjustable screw stop 9.

At the upper end of the arm 1 of the drill holder unit is a cylindrical bearing or trunnion 10 in which is rotatably mounted a shaft 11 which, at the end adjacent to a grinding wheel 31, carries the drill holder and at its opposite end adjacent to the follower unit D carries an interchangeable template 12.

The drill holder (FIGURES 4 and 5) is fixedly mounted on the end of the shaft 11 by means of a bracket mounting 13 and is thus swingable about the shaft axis to move the drill 23 towards and away from the grinding wheel 31. The drill holder comprises a carrier bar 14 which at one end carries a tail stock 18, slidable on said bar and adapted to be locked in any adjusted position axially of the bar by means of a clamping means 21. Fixedly mounted on said bar 14 intermediate the ends thereof is a drill chuck 19 which comprises a pair of pivoted clamping jaws 22 for clamping the drill 23 on the drill holder unit. The drill 23 is rigidly held in position on the drill holder between an axially adjustable feed screw on the tail stock 18 and the clamping jaws 22 of the chuck 19. the clamping jaws engaging the drill on each side of each of the helical lands of the drill, the clamping jaws being held in clamped position by clamping means 24. The carrier bar 14 is slidable in a bracket mounting 13 and in a block 13a, securely mounted in said bracket, and said carrier bar and block are adjustable angularly relative to the axis of shaft 11 about a pivot axis 15 and lockable in adjusted position by a set screw 16 which passes through an arcuate slot 17 in said bracket.

In operation the surface of the point of the drill which is to be ground must be in the same plane as the edge of the template 12, i.e. in the plane indicated by the chain dotted line a in FIGURES l and 5, thus the amount by which the point of the drill projects from the clamping jaws 22 will vary for drills of different diameters. In order to compensate for this variation, i.e. to compensate for the variation in the flute spiral of different diameter drills, the carrier bar 14 is longitudinally adjustable relative to the block 13a by means of an adjusting hand wheel 13b, a setting scale 130 being provided on the block 13a for different drill diameters.

The follower-unit D (see FIGURES 1 and 6) comprises a shaft 25 axially adjustable in a fixed mounting 26 by means of adjusting hand wheel 27 and is held in adjusted position by a clamping means 29. The shaft 25 is provided at its projecting end with a follower 28 having an arcuate surface which engages the template 12.

The grinding wheel assembly B comprises a suitable motor 30 on the driving shaft of which is keyed a grinding wheel 31 the axis of which is set at an angle of from 2 to 10 to the drill point axis (see FIGURE 3) in order to generate the necessary clearance to the chisel edge of the drill when grinding as hereinafter described.

The grinding wheel 31 and the arcuate surface of the follower 28 which abuts the template during grinding of the drill, must be of the same, or substantially the same, radius and correctly positioned relative to each other. This is ensured by a grinding wheel dressing device illustrated in FIGURE 7. This device comprises a dressing bar 32 adapted to be clamped to the drill holder unit C by means of a clamp 33 with one end of said bar positioned opposite to the grinding wheel 31 and the other end opposite to the follower 28, The end of the bar opposite to the grinding wheel carries a pointed diamond 34 for dressing the grinding wheel, whilst the opposite end of the bar is provided with a sharp edge 35 which is arranged to abut the follower 28. In use the drill holder unit is swung outwardly, that is away from the grinding wheel and follower, by means of the handle 10, and the dressholder unit C is then swung back to bring the sharp edge 35 of the bar into contact with the follower 2'8 and the follower is then retracted by the screw adjustment means 26 until the diamond point 34 contacts the periphery of the grindnig wheel 31 thus correlating the diamond point with the follower. The driving wheel motor 30 is then started and the grinding wheel dressed by traversing the drill holder unit C by means of the hand wheel 8, the diamond point thus being moved across the periphery or grinding surface of the wheel. After the grinding wheel has been dressed the dressing bar is removed from the drill holder unit. The machine is thus ready for carrying out the operation of grinding a drill.

The operation of the machine will now be described when used for grinding a centre point drill (illustrated in FIGURE 8) of which the primary clearance 36, secondary clearance 37, the chisel edge 38, and an increased clearance 39 adjacent the chisel edge are to be ground.

A template 12, having a shape suitable for use in grinding a centre point drill, is correctly positioned on shaft 11 and the drill mounted in the drill holder as above described. The drill point is then positioned correctly relative to the edge of the grinding wheel and the template by suitable axial adjustment of the drill holder by means of the adjusting hand wheel 8, the position of the limit stop 9 having first been correctly adjusted. The point of the drill to be ground is then correctly positioned relative to the grinding wheel by adjustment of the drill chuck 19, according to the diameter of the drill indicated on the scale 130, as above described. The drill holder is then pivoted manually about the axis of shaft 11 to bring the flank of the drill point to be ground into contact with the grinding wheel 31 and the template 12 into contact with the follower 28. As the drill holder is rotated about the axis of shaft 11 to bring one flank of the drill point into contact with the grinding wheel, the template 12 causes movement of the drill holder unit as a whole and consequently the drill holder also, about the axis of shaft 2 towards and away from the grinding wheel, but manual rotation of the drill holder keeps the drill point in contact with the grinding wheel. The effect of this is that first the secondary clearance 37 (see FIGURE 8) of the drill is ground and simultaneously the increased clearance 39 adjacent the chisel edge 38 is generated. Continned pivotal movement of the drill holder causes the template 12 to act on the follower 28 in such a way as to bring the primary clearance 36 into engagement with the grinding wheel whereupon said primary clearance and the chisel edge 39 are ground, During the grinding of one flank of the drill the drill is advanced periodically by means of the tail stock feed screw 20 until the flank of the drill is correctly ground. The clamping jaws 22 of the chuck 19 are then released and the drill turned to bring the other flank of the drill into position for grinding the drill, the clamping jaws 22 are then again clamped and the above described operation repeated to grind the other flank of the drill.

It must be understood that the invention is not limited to the particular embodiment herein described and illus- 'trated, but may be modified in" various ways without departing from the scope of the invention as defined in the appended claims. For example the holder unit C need not be necessarily held in its operative position by means of a weight, but the pivot arm 1 may be arranged an an angle of say 45 so that'the holder unit tends to pivot into the operative position under its own weight. Furthermore the holder unit need not be pivotally movable as described to move the drill holder towards the grinding wheel assembly but may be slidably movable towards and away from the grinding wheel assembly.

What is claimed is: 7

1. A machine for grinding twist drills comprising a.

supporting base, a grinding wheel assembly mounted on said base, a'drill holder unit comprising a rotatable shaft, a drill holder mounted on said shaft, a template mounted on said shaft, said drill holder unit being movably mounted on said base to move the template into engagement with a follower fixedly mounted on said base and to move the drill holder and the drill towards the grinding wheel, said drill holder being pivotable about the axis of said rotatable shaft to move the point of the drill into engagement with said grinding wheel, said drill holder comprising a carrier bar mounted on one end of said rotatable shaft, a drill chuck fixedly mounted on said carrier bar and a tail stock slidably mounted on said carrier bar, the drill being held by said drill chuck and said tail stock, and wherein said carrier bar is slidable for longitudinal adjustment in a bracket fixed to said rotatable shaft and said bracket is adjustable to effect angular adjustment of the carrier bar relative to said rotatable shaft.

2. A machine according to claim 1, wherein said follower is mounted on one end of an axially adjustable shaft and means are provided for clamping said shaft in any axially adjusted position.

3. A machine according to claim 1, wherein the axis of the driving shaft of the grinding wheel is set at an angle to the drill point axis.

References Cited UNITED STATES PATENTS ROBERT c. RIORDON, Primary Examiner D. G. KELLY, Assistant Examiner I 'U.S. c1. X.R. 51- 219

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