GB2041798A - Keyless chuck - Google Patents

Abstract

A chuck comprises a base 22 suitable for attachment to the driven shaft of the tool and a collar 20 threadably received by the base. Jaw means 44 are adapted to receive a work piece such as a drill bit, and rotation of the collar relative to the base operates to drive the jaw means into gripping engagement with the work piece. A truncated cone 50 is interposed between the collar and jaw means, and a thrust washer 40 is interposed between the base and jaw means. The structure permits the utilization of plastic for the collar and base. Other parts including the jaws, the force-applying cone, and the thrust washer are produced of hard metal, and these members are arranged so that the hard metal jaws and other hard parts do not damage the plastic. The thrust washer can be attached by means of an oppositely threaded fastener or other suitable means whereby the construction can be utilized in both forward and reverse operation of the tool. <IMAGE>

Description

SPECIFICATION Keyless chuck construction BACKGROUND OF THE INVENTION This invention relates to a chuck design suitable for use in connection with power tools such as a power drill. In such a construction, the chuck is supported by the drill, and the work piece, usually a drill bit, is adapted to be engaged by the chuck.

A typical keyless chuck construction comprises a base and a collar fitted around the base. A threaded connection is provided between the collar and base so that rotation of the collar operates to move the collar axially relative to the base. Jaw means, usually three opposed jaws, are provided with springs normally resisting closing of the jaws. The jaws are located on the base and within the confines of the collar. The spring means urge the jaw means in engagement with the interior surface of the collar, and rotation of the collar serves to increase or decrease the space occupied by the jaw means whereby the jaw means are adapted to be opened and closed.

It is preferred that the jaw means comprise a hard metal, for example, a tool steel, so that the jaw means will be able to withstand the forces applied to the jaw surfaces when the jaws are tightly engaged with a drill bit or the like. Attempts have been made to utilize plastics for chuck parts in previous designs; however, available plastics are not capable of avoiding damage when in use, Plastics are desirable for use in chucks since the weight and mass of chucks can be reduced and the ease of use of the tool correspondingly increases. In addition, the plastics can be produced rapidly at relatively low cost and with very accurate dimensions whereby the efficiency of manufacture of a chuck could be improved.The advantages of plastics have not, however, been sufficient to out-weigh the disadvantages and, therefore, plastics are not used to any significant extent for chuck construction.

Keyless chucks have also been in use. Such chucks do not require the use of a separate tool when a work piece is to be engaged with a chuck or when it is necessary to remove a work piece from a chuck. Keyless chuck designs contemplate the rotation of a collar by hand with the base being held against movement either manually or because of the resistance to rotation of the associated tool drive shaft. Reference is made to United States Patent No. 1,926,760 for an illustration of a typical keyless chuck design.

BRIEF STATEMENT OF THE INVENTION This invention comprises a chuck design suitable for use in association with structures such as a power tool. The invention is particularly suitable as a keyless chuck construction wherein a work piece can be firmly gripped by the chuck without the need for a separate tool for tightening the chuck jaws around the work piece.

The chuck of this invention includes a base and a relatively movable collar whereby jaw means associated with the chuck can be opened and closed in response to rotation of the collar relative to the base.

The invention is particularly directed to a chuck having a collar and base formed of plastics. A force-applying means preferably in the form of a truncated cone is located within the collar in surrounding relationship relative to the jaw means The truncated cone is of a hard metal and it serves to contain stresses developed within the jaw means and in the hard metal. The jaw means are also kept out of direct contact with the plastics collar. Similarly, a thrust washer is provided for supporting the jaw means on the base, and this thrust washer is also formed of a hard metal.

Accordingly, relative movement of the hard jaw means is not directly transmitted to the base, and damage to the base by the jaw means is avoided.

The base can be molded or threaded onto a drive shaft for a tool such as a drill, and this arrangement insures a good connection between the base and tool during rotation of the drive shaft in one direction. Particularly where a threaded connection is involved, and in instances where a reverse movement of the drive shaft is contemplated, the invention provides for an oppositely threaded fastener which holds the thrust washer on the base and which is also threadably engaged with the drill drive shaft. This insures against separation of the base from the drive shaft in either direction of rotation of the drive shaft.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is an elevational view of a hand drill incorporating a chuck of the type contemplated by this invention; Figure 2 is an exploded, perspective view illustrating parts of the chuck; Figure 3 is an end view of the chuck; Figure 4 is a cross-sectional view of the chuck; Figure 5 is a cross-sectional view taken about the line 5-5 of Figure 4; Figure 6 is a cross-sectional view taken about the line 6-6 of Figure 4; and, Figure 7 is a vertical, sectional view of a collar assembly illustrating an alternative jaw design.

DETAILED DESCRIPTION OF THE DRAWINGS Figure 1 illustrates a drill 10 adapted to be held in the hand. A cord 12 is connected to the drill whereby a motor within the drill housing will operate in response to engagement of operating button 14. A drive shaft connected to the drill will then serve to rotate the chuck 16 which supports drill bit 18.

The structure of the chuck 1 6 is best illustrated in Figures 2 through 6. This structure includes a collar 20 and a base 22. The collar defines internal threads 24 which receive the threaded section 26 of the base 22 whereby the collar can be rotated relative to the base for axial movement of the collar relative to the base.

A large internally threaded bore 28 is defined by the base, and the externally threaded portion of the drill drive shaft is received in this bore. The drive shaft defines a smaller bore 32 which is internally threaded for receipt of externally threaded fastener 34. This fastener extends through smooth bore 36 defined by the base whereby the fastener functions as a second means for securing the base relative to the drive shaft.

The head 38 of fastener 34 also serves to secure washer 40 on the end of the base. The washer is countersunk thereby defining inwardly tapered front and back surfaces. The fastener head 34 defines a corresponding taper as does seat 42 defined by the base.

A gripping jaw arrangement made up of jaw sections 44 is received within a cone 50. These jaw sections are connected in an assembly by means of compression springs 46. In accordance with the standard design of such gripping jaws, the springs 46 hold the jaw sections in substantially equally spaced relationship so that the shank 48 of drill bit 18 can be inserted between the jaws and moved inwardly against the head 38 of fastener 34. The jaws can then be pressed inwardly against the shank to provide a gripping relationship with the drill bit.

The mechanism for controlling the position of the jaws includes the truncated cone 50 disposed in engagement with the interior surface 52 of collar 20. The taper of the exterior surface 54 of the cone corresponds with that of the surface 52 so that a snug fitting relationship is achieved.

The springs 46 cause the tapered surfaces of jaw sections 44 to bear against the interior surface 56 of the cone 50. Because of the relationship of the members, the jaw sections also tend to be forced from right to left when considering the position of the structure shown in Figure 4. Thus, the jaw sections tend to be forced against washer 40 by the action of springs 46 in combination with the tapered surfaces of the jaw sections and the cone.

The jaw sections are accordingly forced apart to achieve the maximum possible opening for receipt of the shank 48 of drill bit 1 8. By rotating the collar 20 so that it moves axially from left to right in Figure 4, the jaw sections will automatically be spread apart while maintaining engagement with the surface 56 of the cone and with the washer 40. This permits insertion of shank 48 and thereafter the collar is rotated in the opposite direction whereby the jaw sections will be forced into engagement with the shank to achieve the desired gripping relationship.

It will be noted that there is relative movement of the jaw sections only with respect to the surface 56 of the cone and with respect to the washer 40. The cone 50 and the washer specifically serve to maintain the jaws out of engagement with the base 22 and collar 20.

The jaws 44 are typically produced from a metal of high hardness, and may comprise a tool steel composition. These jaws, the cone 50 and the washer 40 may be forged parts or parts produced utilizing powder metallurgy techniques.

These parts of the assembly are, therefore, highly resistant to abrasion and general wear whereby highly acceptable life for the product is achieved.

The engagement of the jaw sections with the hard drill shank as well as the relative movement between the jaw sections and cone and washer will thus not cause any significant problems.

The collar 20 and base 22 are, on the other hand, not subject to engagement with hard, moving parts. On the contrary, the cone 50 snugly engages surface 52 of the collar, and although this cone is a separate part, the collar surface is not subjected to any significant movement of the cone which would result in abrasion or other deterioration of the collar. Similarly, the washer 40 is seated in a firm position relative to the base 22, and with or without the particular fastener 34, the presence of the washer 40 will not cause any significant wear or other deterioration of the base.

It has been found that with the chuck design described, both the collar 20 and base 22 can be produced from plastics material. By utilizing plastics for these parts, distinct advantages from the standpoint of both manufacturing and operating efficiency are achieved.

In terms of manufacturing efficiency, the collar and base can be molded whereby intricate portions thereof can be faithfully reproduced at high production rates and at lower production costs. Similarly, where the base is molded onto the drive shaft, the accuracy of the manufacturing is enhanced.

The advantages of utilizing molded plastics include the ability to efficiently produce thread designs of the most efficient shape. For example, a 14.5 acme thread design with 16 threads per inch can be readily achieved with plastics molding equipment whereas such thread manufacture would be significantly more expensive in the case of metal parts.

By utilizing plastics, there is no great need to economize in terms of the amount of material employed, for example with respect to thickness of sections. The utilization of larger radii in fact provides advantages in a keyless chuck since the torque input will be increased because of the larger radii involved thereby simplifying the manual operation and reducing the amount of manual force required for achieving the desired gripping force. In this connection, a larger diameter ring section 58 may be formed on the base to provide a grip for the user in cases where the inertia of the gears and motor does not provide sufficient resistance when rotating the collar 20 to tighten the jaws.

As indicated, the use of plastics materials for the base and collar provides operating advantages in addition to the aforementioned manufacturing advantages. The plastics have a lower coefficient of friction and, therefore, there is less resistance to relative movement at the thread interfaces. In a typical construction in accordance with this invention, the base 22 is provided from a nylon composition known for its strength and wear resistance, for example a glass impregnated variety. The collar may be made from an Acetal composition or equivalent. The sliding coefficient of friction (dry) between such materials is 0.1 as compared to a steel on steel coefficient of 0.31 (dry).The input force in the case of steel is thus typically three times or more greater than in the case of plastics and, therefore, the chuck construction of this invention is easier to operate and will achieve greater gripping force in response to the same manually applied collar rotating force.

Increased safety also characterizes the drill of this invention since the possibility of an electrical accident is greatly minimized. Particularly where plastics housings are utilized, the use of the plastics chuck avoids any significant exposure of metal parts. Accordingly, the user is much less likely to experience electrical shock, for example, in the event of an internal problem or in the event of an accidental encounter with a live wire.

In use, the chuck of this invention has also exhibited a higher breakaway torque characteristic. Breakaway torque is the maximum amount of torque that can be transferred from the drive shaft to the drill bit shank or other tool without slippage of the drill bit which is undesirable in use. When comparing the structure of this invention with comparable keyless designs using all steel chucks, it was found that this design achieved a breakaway torque significantly higher than with the all steel chuck. This is believed to be attributable to the higher gripping forces that can be achieved by utilizing the plastics material in the selected fashion described. Attainment of higher gripping forces is also due to the development of a cam-like gripping force that is achieved through the shape of the conical sections of jaw 44 and their engagement with the surface 56 of cone 50.

The utilization of fastener 34 enables achievement of effective gripping in a drill or the like which operates in both forward and reverse modes. Specifically, the fastener 34 is provided with opposite threading compared with the connection of the base 22 and shaft 30 when the construction is characterized by both forward and reverse operation. The separate and opposite threaded connections between the base and shaft 30 insure against any tendency toward separation of these elements irrespective of the direction of rotation of the shaft.

The alternative form of the invention shown in Figure 7 comprises a collar 60 and cone 62 of the general type previously described. In this instance, however, the jaw assembly includes jaw sections 64 which are elongated and which define outwardly extending rearwardly located edges 66.

Two of the jaw sections are shown in Figure 7, but it will be understood that a third jaw section is utilized.

Internal threads 68 of the collar 60 are engaged by the edges 66 in the drawing. Thus, it will be appreciated that the collar can be rotated and run off the base particularly when the operator is changing tools. The design of Figure 7 prevents separation of the jaw assembly under such circumstances. Thus, the springs 70 between the jaw sections automatically force the edges 66 into engagement with the threads 68 to prevent the assembly from falling loose and possibly being lost.

It is contemplated that the edges 66 will engage the threads 68 when the collar has reached a predetermined forward position relative to the base, or the mechanism may be designed so that the action of the springs 70 will not engage the edges with the threads until actual separation of the collar. It will be appreciated that the arrangement of Figure 7 has utility beyond the particular combination described in the earlier figures.

It will be understood that various changes and modifications may be made in the above described construction without departing from the spirit thereof particularly as described in the following claims.

Claims (22)

1. A chuck construction of the type comprising a base, a collar mounted on the base and movable axially relative to the base, and jaw means disposed within said collar and on said base for engaging a work piece to be held by the construction, movement of the collar relative to the base operating to apply force to said jaw means for engaging the jaw means with said work piece, wherein a separate force-applying means is interposed between the interior surfaces of said collar and the exterior surfaces of said jaw means whereby the force to be applied to the jaw means by movement of said collar is transmitted through said force-applying means, said force-applying means holding the jaw means out of engagement with the collar, and thrust means interposed between said base and said jaw means for supporting the means on the base, said thrust means maintaining the jaw means out of engagement with the base.

2. A construction in accordance with Claim 1, wherein said jaw means comprise three separate jaws, spring means urging said jaws outwardly into engagement with the interior surfaces of said force-applying means and into engagement with said thrust means.

3. A construction in accordance with Claim 1 or 2, wherein said collar defines tapered interior surfaces, said force-applying means comprising a truncated cone defining exterior surface substantially conforming to the interior surfaces of said collar, and said jaws defining tapered exterior surfaces engaging the interior surfaces of said cone.

4. A construction in accordance with any preceding claim wherein said collar and said base are formed of plastics material having a low coefficient of sliding friction, said collar defining interior threads and said base defining exterior threads whereby the collar is moved axially of the base by rotation of the collar relative to the base, said low coefficient of friction reducing the force input necessary for achieving firm engagement of said jaws with said work piece.

5. A construction in accordance with claim 4, or claim 5 when dependent thereupon, wherein said cone and said thrust means comprise hard metal elements, said jaws being movable relative to said cone and thrust means during movement of the collar relative to the base, said cone and thrust means protecting the collar and base against engagement with the jaws during movement of the jaws.

6. A construction in accordance with any preceding claim, wherein said thrust means comprises a washer, said base defining an end surface for supporting said washer.

7. A construction in accordance with claim 6, including a fastener securing said washer to said base.

8. A construction in accordance with claim 7, wherein said chuck is adapted to be utilized in association with a threaded driven shaft, means being provided for threadably attaching said base to said shaft for securing the base to the shaft, the fastener holding said washer on the base, being threaded and adapted for reception within a threaded bore of the shaft, said fastener being oppositely threaded when compared with the threaded engagement of the collar and base whereby in use the base is held against movement relative to the shaft in both directions of rotation of the shaft.

9. A construction in accordance with claim 7 or 8, wherein said work piece is held against said thrust washer when the work piece is engaged by said jaws.

10. A construction in accordance with any preceding claim, wherein said chuck is arranged for keyless operation.

11. A construction in accordance with claim 10, wherein said base defines a large diameter gripping ring whereby said base is adapted to be manually held in a stationary position during rotation of the collar relative to the base.

12. A construction in accordance with claim 11, wherein said jaws each define rearwardly located outwardly extending edges, said collar defining internal threads and said base defining mating external threads whereby said collar is rotated for axial movement relative to the base, and wherein said spring means urge said outwardly positioned edges of said jaw means into engagement with said internal threads when said collar is moved to an external forward position of the base.

13. A construction in accordance with claim 12, wherein said spring means hold said edges in engagement with said internal threads when said collar is separated from said base.

14. A chuck construction, substantially as hereinbefore described, with reference to any of Figs 2 or 6 or as modified by reference to Fig 7 of the accompanying drawings.

1 5. A power tool incorporating a chuck construction as claimed in any preceding claim.

16. A power tool according to claim 15, and constituting an electric drill.

17. A power tool according to claim 1 5 or 16, wherein at least that portion of the driven shaft thereof which extends outwardly of the power tool and the base of the chuck are formed in one piece.

18. A chuck construction of the type comprising a base, a collar mounted on the base, said collar defining internal threads and said base defining external threads whereby rotation of the collar moves the collar axially relative to the base, and jaw means comprising separate jaws, and spring means urging said jaws outwardly, and wherein said jaw means define outwardly extending rearwardly located edges, said spring means moving said jaws outwardly as said collar is rotated to move the collar toward the forward nd of the base, said spring means operating to urge said edges into engagement with said internal threads of said collar when the collar is rotated to a predetermined forward position relative to the base.

19. A construction in accordance with claim 18, wherein said edges engage said internal threads when said collar is separated from the base whereby the jaws are held in assembly with the collar by said spring means.

20. A chuck construction substantially as hereinbefore described, with reference to Fig. 7 of the accompanying drawings.

21. A power tool incorporating a chuck construction as claimed in claim 20.

22. The features hereinbefore disclosed, or their equivalents in any novel selection.