GB2067114A - Machine for tapping nuts - Google Patents

Abstract

A nut tapper has a pusher 20 having an end face 22 for engagement with a flange 23 of a nut blank and a recess 24 for receiving the remainder of the blank to prevent nut rotation with a rotary tap 17. Until the blank is pushed onto the tap 17, the flange is held against the end face by spring loaded holding elements 33 and 34. These slide along diverging side walls of a guide 21, pushed by the pusher until their spacing is greater than the nut flange diameter. The pusher is operated by an offset cam-controlled piston-cylinder unit. <IMAGE>

Description

SPECIFICATION Machine for tapping nuts This invention relates to a machine for cutting an internal screw thread in a nut and comprising a carrier for a tap, driving means for rotating the carrier about an axis which coincides with a longitudinal axis of the tap when carried by the carrier and feed means for causing relative axial movement of the tap, when carried by the carrier, and a nut blank to feed the nut blank onto the tap, the feed means including constraining means for constraining the blank against rotation with the tap as the blank is fed onto the tap and an abutment surface which, immediately prior to feeding of the blank onto the tap, faces towards the tap and which engages the blank to control the axial position of the blank relative to the tap. For convenience, such a machine is hereinafter referred to as a "nut tapper".

An example of a known nut tapper is described and illustrated in published U.K. patent application No. 2,002,275 A.

According to a first aspect of the invention, there is provided a nut tapper characterised by the provision of holding means for releasably holding a blank against the abutment surface of the feed means and by an arrangement in which, in use, the constraining means undergoes axial displacement with the blank relative to the carrier and a tap carried thereby as the blank is fed onto the tap.

A nut tapper in accordance with the invention is capable of tapping a nut blank whereof the radially outermost surface is circular, for example a blank having a circular flange at one end.

The feed means preferably includes a reciprocable pusher which presents the abutment surface and there is preferably formed in the pusher a recess for receiving a part of a blank which is to be fed onto the tap, the constraining means being constituted by walls of the recess and the recess extending from the abutment surface in a direction away from the tap carrier.

The preferred form of holding means comprises a plurality of holding elements guided for movement along respective paths which extend alongside a leading end portion of the tap and diverge in the direction of movement of blanks onto the tap.

There may be provided for each holding element a stop which limits travel of the holding element in the direction in which the respective paths of the holding elements converge. The stops for the holding elements are preferably adjustable along the respective paths of the holding elements.

Biasing means may be provided for urging the holding elements towards the abutment surface.

According to a second aspect of the invention, there is provided a method of forming an internal screw thread in a nut wherein a nut blank is releasably clamped to an abutment surface of a pusher, relative movement of a tap and the pusher is then effected to move the abutment surface towards a leading end of the tap and feed the nut blank onto the tap and the nut blank is released from the abutment surface after the nut blank has engaged the tap.

An example of a nut tapper embodying the first aspect of the invention and which is used in performance of a method according to the second aspect of the invention will now be described with reference to the accompanying drawings wherein: Figure 1 shows a diagrammatic representation of the nut tapper partly in cross section, Figure 2 shows on an enlarged scale a fragmentary plan view of certain parts of the tapper at the beginning of a cycle of operation, together with a nut blank which is about to be fed onto a tap, Figure 3 shows the parts of Fig. 2 at a later stage of the cycle, Figure 4 shows a fragmentary cross section of the nut tapper on the line IV-IV of Fig. 2, and Figure 5 shows certain parts in cross section on the line V-V of Fig. 2.

The nut tapper illustrated in the accompanying drawings comprises a body 10, only a small part of which is shown, and which rests on a floor surface. A hollow spindle 11 is supported on the body 10 by means of a bearing for rotation about a horizontal axis 1 2. The bearing restrains the spindle against axial displacement relative to the body. An electric motor 1 3 is provided for driving the spindle, the motor being connected with the spindle by a belt and pulley drive 14.

In the hollow spindle 11 there is releasably secured a carrier 1 5 which is constrained against rotation and axial displacement relative to the spindle. The carrier is formed with an internal passageway which extends through the carrier from one end to the other.

Opposite end portions of the passageway are circular and coaxial with the spindle 11. An intermediate portion of the passageway has an elongate cross section and a radially outer boundary which diverges from the axis 1 2 and then returns towards the axis.

In the carrier 15, there is mounted a tap comprising a shank 1 6 and a threaded leading end portion 1 7. The leading end portion 1 7 is coaxial with the spindle 11 and the shank 1 6 includes a curved intermediate portion corresponding to the intermediate portion of the passageway through the carrier 1 5.

When the nut tapper is in use, the shank 1 6 extends through a row of nuts which support the tap and in turn are supported by the carrier.

The nut tapper further comprises feed means for causing relative axial movement of the tap 16, 17 and a nut blank to feed the nut-blank onto the leading end portion 1 7 of the tap. The feed means includes a vertical chute 1 8 down which nut blanks can slide successively to a first position occupied by a blank indicated -by the reference numeral 1 9 in Fig. 2. When in the first position, the blank is coaxial with the spindle 11 and is spaced somewhat along the axis from the tap. The internal shape of the chute 18 in horizontal cross section corresponds to the shape of the nut blanks so that these are guided to the first position in a predetermined orientation.The particular chute 1 8 illustrated is intended for delivering nuts having at one end a circular flange and therefore has a T-shaped internal cross section with the stem of the T directed along the axis 11 away from the carrier 1 5.

The feed means further includes a pusher 20 which is reciprocable along a rectilinear path parallel to the axis 1 2 from the position illustrated in Fig. 2 to or beyond the position illustrated in Fig. 3. Guide elements 21 mounted on the body 10 guide the pusher. At the end of the pusher which is nearest to the shank 1 6 of the tap, there is provided an abutment surface 22 which is engageable with the flange 23 of the nut blank 1 9 in the first position. The remainder of the nut blank then occupies an upwardly open recess 24 in the pusher. The recess extends from the abut ment surface 22 in a direction away from the tap and is defined by opposed side walls 25 between which the flats of the nut blank are a sliding fit.Downward movement of the nut blank relative to the pusher is limited by lower wall portions 26 of the recess which extend from lower margins of the side walls. Between the wall portions 26 there is a gap through which swarf produced during the tapping operation can fall. At a level above the first position of the nut blank, the side walls 25 diverge to facilitate movement of the nut blank into the recess 24. The side walls 25 and lower wall portion 26 constitute constraining means and act to constrain the nut blank against rotation about the axis 1 2 during the tapping operation.

Resilient biasing means is provided for urg- ing the pusher 20 in a direction towards the shank 1 6 of the tap. This biasing means is in the form of a pneumatic piston and cylinder unit 27, the cylinder of which is secured on the body 10 in a position offset downwardly from the path along which the pusher moves.

Opposite end portions of a piston rod 28 of the piston and cylinder unit protrude from corresponding. ends of the cylinder and one of these ends of the piston rod is connected with the pusher 20 by a transverse arm 29.

For controlling movement of the pusher 20 in a direction towards the-shank 16 of the tap, there is provided a cam and follower mechanism 30 which is driven in co-ordination with rotation of the spindle 11. This cam and follower mechanism includes a cam mounted on the body 10 for rotation about a fixed axis and a follower mounted on the piston rod 28 to engage the periphery of the cam. A toothed belt drive 31 and gear box 32 are provided for transmitting drive from the spindle 11 to the cam.

The general arrangement of the means for reciprocating the pusher and for supporting and rotating the tap may be as described and illustrated in the aforesaid published U.K.

patent application No. 2,002,275 A. However, in the nut tapper described in the published application, the means for constraining the nut blank against rotation during tapping does not move axially with the blank; whereas in the nut tapper illustrated in the accompanying drawings, the constraining means moves with the nut blank along the axis of the tap during the tapping operation.

The nut tapper illustrated in the accompanying drawings also comprises holding means for releasably holding the nut blank against the abutment surface 22 whilst the blank is fed onto the tap. The holding means comprises a pair of holding elements 33 and 34 situated at opposite sides of the axis 1 2 and in front of the abutment surface. Each holding element is guided by a respective one of the guide elements 21 for movement along a respective rectilinear path which diverge from the axis 1 2 in a direction towards the carrier 1 5. At the limit of their travel towards the carrier, the holding elements are spaced apart by a distance exceeding the diameter of the flange 23 so that the nut can pass between the holding elements along the axis 12.At the limit of their travel in a direction away from the carrier, the holding elements are spaced apart by a distance less than the diameter of the flange 23 so that they overlap the flange, as shown in Fig. 2.

Movement of the holding elements is controlled by a control element 35 lying below the path along which the nut blank travels as it is fed onto the tap and partly beneath the pusher 20. Lateral projections on the control element engage in respective slots in the guide elements 21 and the control element is urged along the axis 1 2 in a direction away from the carrier 1 5 by a spring 36 which effectively acts between the control element and the pusher 20. Each of the holding elements 33 and 34 has a downwardly projecting tooth, 37 and 3 & respectively, which engages slidably in a transverse groove formed in the control element so that the holding elements are constrained to move axially with the control element but can move towards and away from the axis relative to the control element.

For limiting travel of the holding elements 33 and 34 in a direction away from the carrier 15, there is provided on each of the guide elements 21 a stop, 39 and 40 respectively. The stops 39 and 40 are releasable from their guide element and can be adjusted to respective selected positions along the guide elements. The stops 39 and 40 are secured on the laterally outwardly facing surfaces of the guide elements and lie in the path of travel of respective parts of the holding elements 33 and 34 so that when the pusher 20 is fully retracted from the carrier 1 5 the holding elements are engaged with the stops.

The stops are set in positions such that when the pusher is fully retracted there is between the holding elements 33 and 34 and the abutment surface 22 a gap somewhat wider than the thickness of the flange 23. This ensures that the holding elements do not obstruct movement of the nut blank into the first position from the chute 1 8.

A cycle of operation of the nut tapper will now be described, assuming that the pusher 20 is fully retracted and the nut blank 1 9 occupies the first position. A further nut blank which occupies the lower end portion of the chute 1 8 rests by its flange on the flange 23.

The spindle 11 is rotated continuously.

The cam and follower mechanism 30 permits the pusher 20 to be moved by the piston and cylinder unit 27 along the axis 1 2 towards the carrier 1 5. This advances the nut blank 1 9 from the first position into engagement with the holding elements 33 and 34.

The holding elements, being acted upon indi-.

rectly by the spring 36, clamp the flange 23 to the abutment surface 22 of the pusher so that a coaxial relation is established between the nut blank and the spindle 11. The pusher, nut blank and holding elements continue to travel towards the carrier 1 5 and the nut blank is thereby fed onto the leading end portion 1 7 of the tap. Since the nut blank is constrained against rotation by the side walls 25, the tap cuts a screw thread in the nut blank. The pusher 20 feeds the nut blank along the entire length of the threaded leading end portion of the tap before withdrawing axially from the threaded nut and returning to its initial position.

As the pusher 20 approaches the limit of its travel towards the carrier 15, the holding elements 33 and 34 move out of overlapping relation with the flange 23 so that the threaded nut is able to move past the holding elements and the holding elements are subsequently able to return to the stops 39 and 40 whilst the nut remains on the tap.

As the nut blank 1 9 moves from its first position, the flange of the nut blank in the lower end portion of the chute 1 8 drops off the flange 23 and seats on the divergent parts of the side walls 25. The side walls slide beneath the flange whilst the pusher approaches the carrier 1 5 and then withdraws to its initial position. As the pusher reaches its initial position, the side wails 25 move from beneath the flange of the next nut blank which is thereby permitted to drop into the first position. The cycle of operation is then completed.

As a newly threaded nut is pushed from the threaded end portion 1 7 of the tap onto the shank 16, the row of nuts on the tap shank is moved along the shank and one nut drops from the free end of the shank.

Claims (10)

1. A nut tapper comprising a carrier for a tap, driving means for rotating the carrier about an axis which co-incides with a longitudinal axis of the tap when carried by the carrier and feed means for causing relative axial movement of the tap, when carrier by the carrier, and a nut blank to feed the blank onto the tap, the feed means including constraining means for constraining the blank against rotation with the tap as the blank is fed onto the tap and an abutment surface which, immediately prior to feeding of the blank onto the tap, faces towards the tap and which engages the blank to control the axial position of the blank relative to the tap, characterised by the provision of holding means for releasably holding a blank against the abutment surface of the feed means and characterised in that, in use, the constraining means undergoes axial displacement with the blank relative to the carrier and the tap carried thereby as the blank is fed onto the tap.

2. A nut tapper according to claim 1 wherein the feed means includes a reciprocable pusher which presents the abutment surface and wherein there is formed in the pusher a recess for receiving a part of a nut blank which is to be fed onto the tap, the constraining means being constituted by walls of the recess and the recess extending from the abutment surface in a direction away from the tap carrier.

3. A nut tapper according to claim 1 or claim 2 wherein the holding means comprises a plurality of holding elements guided for movement along respective paths which extend alongside a leading end portion of the tap and diverge in the direction of movement of nut blanks onto the tap.

4. A nut tapper according to claim 3 wherein there is provided for each holding element a stop which limits travel of the holding element in the direction in which the respective paths of the holding elements converge.

5. A nut tapper according to claim 4 wherein the stops for the holding elements are adjustable along the respective paths of the holding element.

6. A nut tapper according to claim 5 wherein the biasing means are provided for urging the holding elements towards the abutment surface.

7. A method of forming an internal screw thread in a nut wherein a nut blank is releasably clamped to an abutment surface of a pusher, relative movement of a tap and the pusher is then effected to move the abutment surface towards a leading end of the tap and feed the nut blank onto the tap and the nut blank is released from the abutment surface after the nut blank has engaged the tap.

8. A nut tapper substantially as herein described with reference to and as illustrated in the accompanying drawing.

9. A method of forming an internal screw thread in a nut substantially as herein described with reference to the accompanying drawing.

10. Any novel feature or novel combination of features disclosed herein or in the accompanying drawings.