GB2052323A - Chuck and tool assembly incorporating said chuck - Google Patents

Abstract

A chuck, especially for a rotary impact tool has a chuck body formed with a larger (2) and smaller section (3) with a screw threaded bore (4) formed at one end of the larger section (2) for threadedly connecting the chuck to a shaft for rotation in a given direction. Cylindrical bores (5) are formed in the body (2, 3) to receive respective jaws (6) formed along outwardly facing surfaces with screw thread segments (12). A sleeve (8) rotatably mounted on the large diameter section (2) is axially constrained thereto and has a nut (10) received therein and provided with a female screw thread (11) engaging the screw thread segments (12). The inclination and pitch of the threads of the nut and the segments are such that rotation of the sleeve (8) in the same direction as the given chuck rotation direction displaces said jaws (6) in the bores (5) for the clamping of a tool. <IMAGE>

Description

SPECIFICATION Chuck and tool assembly incorporating said chuck This invention relates to a tool chuck, especially a drill chuck for a power tool, e.g. a rotary drill and especially a percussion drill, and to a tool assembly including the power unit and the chuck.

It is common practice to provide machine tools and hand-held power tools with tool-holding chucks whose jaws grip a tool, such as a drill bit, upon rotation of a member of the chuck serving to advance and retract the jaws.

Typical of the tools with which such chucks are used are hand-held power tools such as electrical drills, which generally comprise a motor in a housing, a handle for enabling the housing to be gripped and provided with a trigger switch for turning on or off the motor, and possibly means for adjusting the speed of the drill.

Electrical drills are also provided with an impact or percussion capability, e.g. to facilitate the penetration of masonry or concrete, the drill chuck being both rotated and driven axially to provide a combined rotary and impact motion to the bit. The typical chuck for such tools can comprise a chuck body which is attached by a screw thread to the shaft of the motor or gearing disposed between the motor and the chuck, this body having two cylindrical sections of large and small diameter respectively disposed adjacent to the machine housing and remote therefrom.This body is formed with a plurality of inclined channels converging toward the axis at the end of the small section remote from the attachment screw thread, in which jaws are guided, the outer surfaces of these jaws being provided with partial threads which cooperate with a female screw thread upon a ring which can be affixed to a sleeve rotatable on but axially constrained on the aforementioned body.

When the sleeve is rotated, therefore, the jaws are advanced or retracted depending upon the sense of rotation.

The screw thread for attaching the body to the shaft allows attachment by rotation of the chuck in the same sense as the shaft rotates for drilling operation. However, the rotation of the ring and its screw to tighten the chuck jaws against a tool is effected in the opposite rotational sense, i.e. opposite the sense of rotation of the motor during normal drive.

In the usual method of inserting a tool, such as a drill bit having a cylindrical shank, the sleeve is rotatable until the jaws are sufficiently retracted, the shank of the bit is inserted, and the sleeve is rotated to advance the jaws until they lock the bit in place.

Once the bit is securely held, a chuck key is used to tighten the chuck.

The key usually has a central pin surrounded by a crown of teeth which engage, like a pinion, teeth along the edge of the sleeve remote from the drill housing so that rotation of the key will drive the sleeve.

The clamping of the chuck in this manner has not, however, been found suitable under all conditions and in all applications.

With a percussion or impact drill, for example, a conventional chuck of the type described tends to open because of the impact and vibrational movement, the forces being such that the screw thread of the sleeve tends to open and rotate the sleeve in the opening sense during rotation.

It has been proposed to overcome this disadvantage by providing at the rear end of the chuck, i.e. the end facing toward the housing, an elastomeric toroidal joint between the chuck body and the sleeve which will frictionally retard opening. However, it is difficult to overcome this friction by manual rotation of the sleeve for rapid opening and closing movements thereof as may be necessary when a number of drills must be used in succession and the drills are of different diameters.

While rotation of the key will generate sufficient force to overcome the friction, the use of the key for large opening and closing movement is not conve nient and is time-consuming so that the productivity of the tool is seriously diminished by devices intended to frictionally retard opening of the chuck.

It has also been proposed to provide a radial screw or like pressure member to retain the sleve in a clamping position during periods of use. However, these techniques introduce elements which involve the use of masses, however small, which are eccentric and cause vibration upon rotation of the chuck.

It is an object of the present invention to provide a chuck and a tool assembly incorporating the chuck which overcomes these disadvantages and, in a simple and convenient manner, facilitates locking of the tool in the machine so that opening during percussive action is prevented.

It is also an object to provide an improved self-tightening chuck for the purposes described.

When a chuck is utilized in a rotary impact drill of the afore-described type and has basically the elements discussed above, it is possible to overcome all the disadvanatages enumerated by providing the sense of the screw thread of the sleeve and the mating screw threads of the jaws opposite to the customary configuration, i.e. that rotation of the sleeve in the jaw-closing sense is in the same sense as the rotation of the shaft of the motor. In other words, the locking sense of rotation of the sleeve corresponds to the sense of rotation of the motor shaft during drilling and rotary impact operations.

This provides an automatic locking of the jaws during percussion operations.

According to the present invention, therefore, a chuck, especially for a powertool having a shaft rotatable in a given direction during operation comprises a chuck body having a large diameter cylindrical section and a small diameter cylindrical section coaxially aligned along the axis of rotation of the chuck, screw threaded means formed at one end of said large diameter section for connecting said chuck to said power tool shaft; at least three cylindrical bores formed in said body and converging toward said axis in the direction of the opposite end of said body; respective jaws slidably receivable in said bores and formed along outwardly facing surfaces with screw thread segments; a sleeve rotatably mounted on said large diameter section and axially constrained thereon; a nut received in and fixed to said sleeve and provided with a female screw thread engaging said screw thread segments, said screw thread of said nut and said segments being pitched so that rotation of said sleeve in said given direction displaces said jaws in said bores toward said axis for the clamping of a tool in said chuck; crown gearing formed on one end of said sleeve; and a radial bore formed in said body adjacent said end of said sleeve for receiving a key adapted to engage said crown gearing and rotate said sleeve.

The crown of teeth on the sleeve is preferably formed at the end thereof facing towards the motor, while a cylindrical extension of the body is provided with a hole to receive the pin of the key for rotating this sleeve. This arrangement enables the key to be rotated in clockwise sense, corresponding to normal key rotation for locking, and avoids having to have the worker rotate the key in a counterclockwise sense normally associated with unlocking.

The above and other objects, features and advantages of the present invention will become more readily apparent from the following description of embodiments, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a perspective view, partly broken away, through a chuck embodying the invention; and Figure2 is an axial cross-sectional view through a preferred embodiment of chuck embodying the invention, shown in a position in which it grips a tool.

The chuck shown in Figure 1 comprises a chuck body of generally cylindrical configuration having a large diameter section 2 and a small diameter section 3 which is bevelled at 3'. The body 2, 3 is formed with cylindrical passages 5 which converge toward the axis A forwardly at angles of about 15 and receive cylindrical jaws 6 which are provided along their inner surface with chamfers 7 defining gripping edges. A blind bore 4 whose screw thread tightens the chuck on the shaft of a power-tool (not shown) by rotation in the same sense as rotation of the shaft, is formed atthe axial end of section 2 that will be adjacent to the power tool.The jaws 6 are formed along outwardly facing suraceswith teeth 12 corresponding to segments of a screw thread which are engageable by an internal screw thread 11 of a ring 10 constituting a nut and received in an annular groove 9 formed in the large diameter section 2. The nut 10 is fixed to a cylindrical sleeve 8 whose outer periphery 8' is knurled to facilitate gripping, the sleeve 8 being axially constrained on the body, 2, 3 by shoulders 8a and Sb. Upon rotation of the sleeve 8, therefore, the jaws can be advanced in the direction of arrow B or retracted in the opposite direction.Along the edge of the sleeve 8, remote from the bore 4 there is provided a crown 13 of teeth which can be engaged by teeth of a conventional chuck key whose pin can be inserted into a blind bore 14formed readily in the small diametersection 3. Thefemale screwthread of member 10 and the male screw thread portions 12 of jaws 6 are inclined and pitched so that rotation of the sleeve in the same sense as the shaft of the power tool tightens the jaws 6 against a tool bit.

In the embodiment shown in Figure 2, in which similar numerals are used to designate similarly functioning parts, the crown is not provided along the edge of the sleeve 8 remote from the bore 4; instead, the cylindrical portion 2 of the body is extended axially beyond the sleeve 8 at 15 remote from where a tool bit 19 is gripped by the jaws 6. The end of the sleeve 8 adjacent the extension 15 is provided with a tubular bushing 16 secured to the sleeve to be rotatable therewith. This bushing carries a crown gear 17. A radial blind bore 18 is provided in the extension 15 to receive the pin of a conventional chuck key which can rotate the sleeve 8. Thus, with the screw thread of nut 10 having the same inclination as in Figure 1,this embodiment permits the key to be rotated in the clockwise sense to tighten the jaws against the tool bit.

Claims (6)

1. A chuck, especially for a power tool having a shaft rotatable in a given direction during operation, said chuck comprising:- a chuck body having a large diameter cylindrical section and a small diameter cylindrical section coaxially aligned along the axis of rotation of the chuck, screwthreaded means formed at one end of said large diameter section for connecting said chuck to said power tool shaft; at least three cylindrical bores formed in said body and converging toward said axis in the direction of the opposite end of said body; respective jaws slidably receivable in said bores and formed along outwardly facing surfaces with screw thread segments; a sleeve rotatably mounted on said large diameter section and axially constrained thereon; a nut received in and fixed to said sleeve and provided with a female screw thread engaging said screw thread segments, said screw thread of said nut and said segments being pitched so that rotation of said sleeve in said given direction displaces said jaws in said bores toward said axis for the clamping of a tool in said chuck; crown gearing formed on one end of said sleeve; and a radial bore formed in said body adjacent said end of said sleeve for receiving a key adapted to engage said crown gearing and rotate said sleeve.

2. A chuck as in Claim 1, wherein said large diameter section of said chuck body has an extension beyond said sleeve and formed with said radial bore, said crown gearing being formed on the end of the sleeve adjacent to the means for connecting said chuck to said shaft.

3. A power tool fitted with a chuck as defined in Claim 1 or Claim 2.

4. A chuck substantially as hereinbefore described with reference to Figure 1 of the accompanying drawings.

5. A chuck substantially as hereinbefore described with reference to Figure 2 of the accompanying drawings.

6. A power tool fitted with a chuck substantially as hereinbefore described with reference to either of Figures 1 or 2 of the accompanying drawings.