GB2209007A - Positive feed drill with bearing supported shafts - Google Patents

Abstract

The drill (10) has a shaft assembly comprising a drive shaft (24) and drill shaft (82). In order to maintain coincidence of the axis of rotation of the shafts (24, 82) the shaft (24) is mounted in two ball bearings (26, 150) and roller bearing (152). The drill shaft (82) is mounted in a bush (84) and at the point of contact between the two shafts a thrust bearing (88) is provided. This transmits an axial force from a feed drive shaft (56) via a ring (90) to the drill shaft (82). A further needle roller bearing (86) is provided between the thrust bearing and the bush. <IMAGE>

Description

POSITIVE FEED DRILLS This invention relates to positive feed drills in which there is a drive both for the rotation of the drill spindle and the axial feed of the drill spindle. It is common in such drills for the drill spindle to be in two parts, one of the parts of the spindle being capable of being fed axially whilst also rotating. A problem which arises during the operation of such drills is that the axis of the two parts of the spindle do not remain coincident, or the axis either singly or in combination distort, particular at the extremity of the axial feed, causing incorrect machining.

The present invention seeks to provide a positive feed drill in which the axis of the two parts of the drill spindle remain coincident and straight throughout the extent of axial feed.

Accordingly, the present invention provides a positive feed drill having a rotatably drivable shaft assembly, the shaft assembly being in at least two parts axially movable relatively one to another, the two parts of the shaft assembly being located in bearings at their extremities and at the point of contact between the two parts of the shaft assembly.

The shaft assembly can comprise a drive shaft having a driven gear mounted thereon and a drill shaft, the two shafts being connected together by a spline, the extremities of each of said shafts being mounted in at least one bearing, and a bearing also being provided continuously at the connection between the two shafts.

The bearings at the extremity of the drive shaft can comprise at least one ball bearing and at least one roller bearing and the bearing at the extremity of the drill shaft can comprise a plain bush.

The bearing at the connection between the two shafts can comprise a thrust bearing engageable with a feed drive shaft of the drill.

The present invention will now be more particular described with reference to the accompanying drawings in which Fig. 1 is a sectional elevation of one form of positive feed drill according to the present invention, Fig. 2 is an end elevation of the feed mechanism housing of the drill shown in Fig. 1, Fig. 3 is a part section on line 3-3 in Fig. 1, Fig. 4 is a sectional elevation of a hand drive of the drill shown in Fig. 1 and Fig. 5 shows a motor drive for the drill shown in Fig. 1.

Referring to the drawings and in particular to Fig. 1, a positive feed drill 10 has a casing which comprises a gear box 12 with a cover 14, and a first support tube 16 attached to the end of the gear box 12 opposite to that of the cover 14 by means of screws (not shown). A second support tube 18 is secured to the first support tube 16 by means of screws (not shown) which also pass through and hold in place a feed mechanism 20 which is thereby clamped between adjacent ends of the first and second support tubes.

The gear box 12 contains a gear 22 mounted on a secured to a main drill shaft 24 of a shaft assembly, the gear 22 being also mounted within a ball bearing 26 located in the cover 14. The gear 22 is driven by an air motor 28 (see Fig. 5) through a shaft 30 and a gear 32 which meshes with the gear 22, the shaft 30 being mounted within a ball bearing 34 which is also mounted in the cover 14. A layshaft 36 is mounted in a needle roller bearing 38 in a bearing support plate 40 and a needle roller bearing 42 in the gear box 12. A helical axial feed gear 44 and a driven feed gear 46 are also mounted on and secured to the shaft 36. A worm wheel 48 (see Fig. 4 also) engages with a pinion gear 50 on the shaft 24 and the gear 44 on the shaft 36.The gear 46 also on the shaft 36 engages with a clutch mechanism indicated generally at 52 in order to drive a feed drive comprising a drive shaft 54 to which is keyed a driven shaft 56, the drive shaft 54 being located in a ball bearing 58 secured in the wall of the gear box 12.

The clutch mechanism 52 comprises a gear 60 which engages with the gear 46, a spring plate 62 which is prevented from moving axially by means of set screws 64, a shim 66 in contact with the spring plate and a spring 68 bearing against the shim plate and a surface of the gear 60. The action of the spring urges the gear into contact with a plurality of balls 70 in a cage 72. The balls are seated in recesses 74 in the gear 60 and recesses 76 in a flange 78 on the drive shaft 54.

The drive shaft 54 has a spline connection 80 with a drill shaft 82 which is mounted in a bush 84 and a double needle roller bearing 86. A double taper roller thrust bearing 88 is interposed between the end of the drive shaft 56 and the drill shaft 82 and the bearing 88 is in contact with a thrust washer 90 on the drill shaft 82.

The driven shaft 56 of the feed drive is formed with an external thread and rotates with the driven shaft 54 of the feed drive but is movable axially relative to the shaft 54 by the operation of the feed mechanism 20.

The feed mechanism 20 comprises a housing 92 (Fig. 2) having an outer annulus 94 with openings 96 for the passage of the screws securing the support tubes 16 and 18 together with the feed mechanism 20 being clamped between the two support tubes. The housing 92 has a central bore 98 and an inner annulus 100 having three equispaced radial openings 102. A cam plate 104 is mounted within the housing 92 and has three slots 106 and pins 108 mounted in rollers 110 are located in each cam slot 106, each pin carrying a part nut 112 located within a respective one of the openings 102. The slots 106 are so shaped at each end that the pins 108 carrying the part nuts 112 cannot move along the slot thereby preventing radial movement of the part nuts, particularly when the part nuts are in engagement with the thread on the shaft 56.Each part nut is formed with a thread which is engageable with the thread on the shaft 56. The cam plate has a feed handle 114 terminating in a knob 116, the feed handle extending through a slot 118 formed in the annulus 94 of the housing 92. The cam plate 104 and the housing 92 are provided with a detent mechanism 120 in order to assist in maintaining the cam plate in a desired position, for example, when the feed handle is at one or both ends of the slot 118. The detent mechanism comprises a ball 122 loaded by a spring 124 into a recess 126 formed on the cam plate.

Referring particularly to Fig. 4, the worm wheel 48 is attached to a selector shaft 128 by means of a key 130 loaded by a spring 132, the shaft being mounted in bearings 134 and 136 in the gear box 12. The shaft 128 has a further gear 138 and a spring loaded plunger 140 engageable with one or other of the recesses 142, 144 in an outer tubular shaft 146. The shaft 128 is movable axially and can be rotated by means of the handle 148.

The main shaft 24 as well as being mounted in the bearing 26 by means of the gear 22 is also mounted in a further ball bearing 150 in the bearing support plate 40 is also mounted in a double needle roller bearing 152 which is located between the shaft 24 and the drive shaft 54 of the feed drive.

In use, a drill chuck on a tapered arbor (not shown) is positioned within the end opening in the drill shaft 82. The air motor 28 is operated to drive the gear 22 on the shaft 24 via the air motor shaft 30 and gear 32. Thus, the drill shaft 82 is also rotatably driven by virtue of the spline connection 80 with the drive shaft 24.

The rotation of the shaft 24 rotates the worm wheel 48 and thereby the gear 44, shaft 36 and gear 46. The engagement of the gear 46 with the gear 60 and the operation of the clutch mechanism 52 causes rotation of the shaft 54 of the feed drive and the shaft 56 by virtue of the keyed connection between the two shafts 54 and 56.

In order to engage the feed to drive the drill shaft 82 axially relative to the shaft 24, the cam plate 104 is moved by moving the feed handle along the slot 118 in the housing 92 of the feed mechanism. The camming action of the slots 106 cause the part nuts 112 to move axially inward through the openings 102 in the annulus 100 of the housing 92 and the threads on the part nuts engage with the external thread on the shaft 56 of the feed drive.

Since the shaft 56 is rotating, the engagement of the shaft with the part nuts causes the shaft 56 to move axially on the keyed connection with respect to the shaft 54 and through the thrust bearing 88 and thrust washer 90 causes the drill shaft 82 to move axially relative to the shaft 24 on the splines forming the spline connection 80.

The drill will continue to rotate and the axial feed will continue to function until either the operation of the air motor 28 is discontinued, the feed mechanism is disengaged by returning the feed handle 114 on the cam plate 104 to its original position in the slot 118 or when the end of the thread on the shaft 56 is reached. In that latter event, or if the combination of drill RPM and feed rate are too excessive, then the clutch mechanism 52 will operate and the gear 60 will slip on the balls 70 against the load set by the spring 68. Once slipping takes place the drive to the shaft 54 will be discontinued and any axial movement of the drill shaft 82 will cease. Thus the clutch mechanism 52 provides an overload safety device. It will be apparent that the load exerted by the spring 68 can be adjusted to suit the overload limit which is required for any particular circumstance.

The provision of the bearings 26, 150 and 152 at one extremity of the shaft 24, the thrust bearing at the point of contact between the shafts 24 and 82 and the bush 84 on the drill shaft 82 combine to ensure that the drill rotational drive remains rigid and the axis of rotation of the shafts 24 and 82 remain coincident throughout the extent of the feed.

The feed mechanism 20 provides a simple, rugged and efficient means of engaging the axial feed from the shaft 56 to the drill shaft 82 which will not disengage under load, not only by virtue of the inherent features of the design, but assisted by the operation of the detent mechanism 120.

In the event that it is required to provide a hand feed whilst the drill shaft 24 is driven by the air motor, the selector shaft 128 is moved axially to disengage the shaft from the worm wheel and to engage the gear 138 with the gear 44. The operation of the handle 140 will then enable the operator to drive the feed to the gears 138, 44, 46 and the clutch mechanism 52 at the desired rate.

Claims (1)

1. (1) A positive feed drill having a rotatably drivable shaft assembly, the shaft assembly being in at least two parts axially movable relatively one to another, the two parts of the shaft assembly being located in bearings at their extremities and at the point of contact between the two parts of the shaft assembly.

   (2) A positive feed drill as claimed in claim 1 in which the shaft assembly includes a first shaft having a gear mounted thereon arranged to be driven from a power source and a second shaft in splined engagement with the first shaft and having a recess arranged to receive a tool holder, the shaft assembly including a bearing located continuously in the region of the splined connection between the two shafts.

   (3) A positive feed drill as claimed in claim 1 or claim 2 in which the first shaft is mounted in at least two bearings at the end remote from the splined connection with the second shaft.

   (4) A positive feed drill as claimed in claim 3 in which the first shaft is mounted in two bearings, one on each side of said gear.

   (5) A positive feed drill as claimed in claim 3 or claim 4 in which the first shaft is mounted in a further bearing located between the first shaft and a drive member of the axial feed of the drill.

   (6) A positive feed drill as claimed in any one of the preceeding claims in which the second shaft is mounted in a bush.

   (7) A positive feed drill as claimed in claim 6 in which the second shaft is also mounted in a further roller bearing.

   (8) A positive feed drill as claimed in any one of the preceeding claims in which the bearing located in the region of the splined connection between the two shafts is a thrust bearing engageable with a shaft of the axial feed of the drill.

   (9) A positive feed drill having a shaft assembly constructed and arranged for use and operation substantially as herein described and with reference to Fig. 1 of the accompanying drawings.