The present invention relates to a collet, and particularly to a collet for use in a tool holder. More particularly, the present invention relates to collet adapted to be received in a long-taper tool holder and secured by a collar.

According to the present invention, a collet is provided having a left frustum, a right frustum, and a center portion positioned between the left and right frustums. The left frustum includes a frustoconical first outer surface having a positive slope, a first inner surface, a first left end, a first right end, a first gap extending between the first inner surface and the frustoconical first outer surface, and a plurality of first slits extending from the first left end to the first right end. Each first slit has an open end at the frustoconical first outer surface and a closed end terminating short of the first inner surface. The center portion includes a second outer surface, a second inner surface, a second left end coupled to the first right end, a second right end, a second gap extending between the second outer surface and the second inner surface, and a plurality of second slits extending from the second left end to the second right end. Each second slit has an open end at the second outer surface and a closed end terminating short of the second inner surface. The right frustum includes a frustoconical third outer surface having a negative slope, a third inner surface, a third left end coupled to the second right end, a third right end, a third gap extending between the third inner surface and the frustoconical third outer surface, and a plurality of third slits extending from the third right end to the third left end. Each third slit has an open end at the frustoconical third outer surface and a closed end terminating short of the third inner surface.

According to preferred embodiments of the present invention, the left and right frustums and the center portion cooperate to provides a C-shaped sleeve and a series of more than three teeth. The C-shaped sleeve includes first and second longitudinally extending edges arranged in spaced-apart relation to one another to define the first, second, and third gaps. The C-shaped sleeve includes a round outer boundary

and an inner surface including the first, second, and third surfaces to define a chamber adapted to receive a tool therein.

The series of teeth are appended to the round outer boundary of the C- shaped sleeve and arranged to cause each pair of adjacent teeth to lie in circumferentially spaced-apart relation to one another on the round outer boundary to define a narrow slit therebetween extending along the length of the C-shaped sleeve. Each tooth includes a root appended to the round outer boundary of the C-shaped sleeve and a crown appended to the root. The crown of each tooth including first, second, third, fourth, and fifth outer surfaces extending in sequence from a left end of the tooth to a right end of the tooth.

The first surface has a positive slope and the fifth surface has a negative slope. The second, third, and fourth outer surfaces cooperate to define a transverse channel extending across the width of the tooth.

The teeth also cooperate to define a plurality of first and second slits.

Each of the first slits include an open end at the outer surface and a closed end terminating short of the inner surface. Each of the second slits including an open end at the outer surface and a closed end terminating short of the inner surface. The closed ends of the first slits are spaced apart from the inner surface by a first distance and the closed ends of the second slits are spaced apart from the inner surface by a second distance that is greater than the first distance.

Additional features of the invention will become apparent to those skilled in the art upon consideration of the following detailed description of preferred embodiments exemplifying the best mode of carrying out the invention as presently perceived.

Brief Description of the Drawings The detailed description particularly refers to the accompanying figures in which: Fig. 1 is a perspective view of a tool holder showing the tool holder including a shank body having a conical portion, an annular tool-change flange beneath the conical portion, and a collet grip portion beneath the annular tool-change flange, a collet grip collar coupled to the collet grip portion, and a collet positioned within the collet grip collar and the collet grip portion of the shank body;

Fig. 2 is a perspective view of the collet included in Fig. 1 showing the collet including a collet body having a radially outer surface adapted to engage the collet grip portion and collet grip collar and a radially inner tool-grip surface adapted to grip a tool (not shown), the collet body formed to include a wide gap extending between the outer and inner surfaces, the collet body further including a left frustum, a right frustum, and a recessed center portion cooperating with the left and right frustums to define a groove in the collet body between the frustums, and the frustums and the center portion cooperate to provide a plurality of circumferentially spaced teeth defining narrow slits therebetween; Fig. 3 is a cross-sectional view of the tool holder taken along line 3-3 of Fig. 1 showing the collet grip portion of the shank body including an outer surface formed to include male screw threads and an inner surface having a tapered cam portion in engagement with the right frustum of the collet body and showing the collet grip collar including an inner surface formed to include female screw threads and a tapered cam portion in engagement with the left frustum of the collet body; Fig. 4 is a perspective view similar to Fig. 2 showing one of the teeth; Fig. 5 is a front end view of the collet showing the radially inner tool-grip surface defining a tool chamber adapted to receive the tool, the wide gap extending between the radially inner and outer surfaces of the collet body, the narrow slits including open outer ends that extend to the outer surface and closed inner ends extending toward, but short of, the inner surface, and the plurality of teeth coupled to a C-shaped sleeve at the closed inner ends of the narrow slits; Fig. 6 is a side elevation view of the collet body of Fig. 2 showing the left frustum having a positive slope relative to the central axis, the right frustum having a negative slope relative to a central axis, and the groove extending around the central axis; Fig. 7 is a cross-sectional view taken along line 7-7 of Fig. 5 showing the wide gap bounded by a side edge and upper and lower collet teeth extending from the radially outer surface to the C-shaped sleeve (in phantom); Fig. 8 is a cross-sectional view of the collet body taken along line 8-8 of Fig. 5 showing upper and lower collet teeth coupled to the C-shaped sleeve; Fig. 9 is a front end view of an alternative embodiment collet body having sixteen narrow slits;

Fig. 10 is a front end view of another alternative embodiment collet body having alternating long and short slits; Fig. 11 is an enlarged view of a portion of Fig. 10; and Fig. 12 is a diagrammatic view showing force transmitted from a force generator through an interrupted transfer surface to an intermediate transfer member, through the intermediate transfer member to a continuous grip surface, and through the continuous grip surface to a work surface.

Detailed Description of the Drawings A tool holder 10 is shown in Fig. 1. Tool holder 10 is adapted to fit within a machine center (not shown) to hold a tool (not shown) in relation to the machine center. Tool holder 10 includes a shank body 12, a collet grip collar 14 and a collet 16.

Shank body 12 includes a conical portion 18, an annular tool-change flange 20 beneath conical portion 18, and a collet grip portion 22 beneath annular tool-change flange 20.

Collet 16 is sized to grip a particular diameter tool having a cylindrical shank (not shown) and a workpiece engaging edge configured to engage and form the workpiece into a desired shape. A series of collets 16 are provided to grip different diameter tool shanks as discussed below. Collet 16 includes a collet body 24 having an radially outer surface 26 adapted to engage collet grip portion 22 and collet grip collar 14 and a radially inner tool-grip surface 28. Radially inner tool-grip surface 28 has an inside diameter 30 and defines a tool-receiving chamber 32 configured to receive the shank of the tool.

Collet body 24 is configured to circumferentially flex and"wrap around" the tool shank to provide gripping engagement therebetween. Collet body 24 is formed to include a wide gap 34 extending between radially outer and inner surfaces 26,28 to aid in providing the flexibility. Collet body 24 also includes a left end 36, a right end 38, and a plurality of teeth 40 extending between left and right ends 36, 38 that also aid in providing the flexibility. Collet teeth 40 define a series of circumferentially spaced narrow slits 42 therebetween that aid in the circumferential flexibility of collet body 24.

As shown in Fig. 6, collet body 24 includes a left frustum 44, a cylindrical center portion 46, and a right frustum 48. Cylindrical center portion 46 is recessed to provide an annular clip-receiving groove 50 in collet body 24 between left

and right frustums 44,48. According to an alternative embodiment, the center portion is not recessed.

As shown in Fig. 3, collet grip portion 22 of shank body 12 includes an outer surface 52 formed to include male screw threads 54 and an inner surface 56 having a tapered cam portion 58 adapted to engage right frustum 48 of collet 16. Collet grip collar 14 includes an inner surface 58 formed to include female screw threads 62 and a tapered cam portion 64 adapted to engage left frustum 44 of collet 16.

Collet grip collar 14 secures collet 16 onto shank body 12 and together with shank body 12 cams collet 16 into engagement with the tool. This camming squeezes collet 16 into engagement with the tool to securely grip and mount the tool to tool holder 10. Collet grip collar 14 is screwed onto shank body 12 along a central axis 66. This axial motion forces tapered cam portion 64 of collet grip collar 14 into engagement with left frustum 44 of collet body 24. This axial motion also forces right frustum 48 of collet body 24 into engagement with tapered cam portion 58 of shank body 12. These engagements force collet body 24 to contract toward central axis 66.

As collet body 24 contracts, tool chamber 32 gets smaller and radially inner tool-grip surface 28 grips the tools. Wide gap 34 facilitate this contraction of collet body 24 by providing room for collet body 24 to circularly flex.

Radially inner tool-grip surface 28 is a continuous surface that engages the tool shank and circularly flexes to provide substantially continuous contact between collet body 24 and the tool shank during gripping. This continuous contact between collet body 24 and the tool provides significant normal forces between radially inner tool-grip surface 28 and the tool shank. These normal forces result in significant frictional forces along the circumference of the tool shank that result in significant tool hold torque required to hold the tool during machining operations. If collet body 24 did not have continuous contact around the tool, the tool hold torque would be significantly reduced and the tool could slip during machining operations.

Narrow slits 42 include outer open ends 68 that extend to radially outer surface 26 and closed inner ends 70 that extend toward, but short of, radially inner tool- grip surface 28 to provide a C-shaped sleeve 72. Collet teeth 40 cooperate to define outer surface 26 so that force generated when collet grip collar 14 is screwed onto shank body 12 is transmitted to collet teeth 40. This force is then transmitted from collet teeth

40 to C-shaped sleeve 72 and tool shank to provide the gripping force required to hold the tool in the tool holder during actuation of the tool holder in the machine center.

A plurality of hinge portions 74 are positioned between inner ends 70 of narrow slits 42 and radially inner tool-grip surface 28 of collet body 24 to define C- shaped sleeve 72. C-shaped sleeve 72 includes first and second longitudinally extending edges 76,78, radially inner tool-grip surface 28, and a round outer boundary 80.

Radially inner tool-grip surface 28 extends between first and second edges 76,78 to provide a continuous surface. Collet teeth 40 are coupled to C-shaped sleeve 72 at outer boundary 80 as shown in Figs. 4 and 7.

Each tooth 40 extends axially away from C-shaped sleeve 72 so that gripping force introduced to collet teeth 40 is transferred through C-shaped sleeve 72 to the tool shank. As shown in Fig. 4, each tooth 40 includes a root 82 appended to outer boundary 80 of C-shaped sleeve 72 and a crown 84 appended to root 82. C-shaped sleeve 72 connects collet teeth 40 together through hinge portions 74 to provide hinge points around radially inner tool-grip surface 28 that allow C-shaped sleeve 72 to circularly flex. As shown in Fig. 5, each collet tooth 40 has a radially inner arc thickness 86 measured between closed ends 68 of narrow slits 42 defined by adjacent collet teeth 40 and a radially outer arc thickness 88 measured between open ends 70 of narrow slits 42 defined by adjacent collet teeth 40.

As shown in Fig. 4, each tooth 40 includes a left-end surface 90 and a parallel right-end surface 92 facing away from left-end surface 90 that aid in defining left and right ends 36,38. Each tooth 40 further includes first and second outer surfaces 94, 96 defining a positively sloping frustoconical outer surface 98 of left frustum 44 and a negatively sloping frustoconical outer surface 110 of right frustum 48.

Each tooth 40 further includes parallel first and second side surfaces 112, 114 and a third side surface 116 extending between first and second parallel side surfaces 112,114 as shown in Fig. 7. First, second, and third side surfaces 112,114,116 cooperate to define a transverse channel 118 extending through the width of tooth 40.

First and second side surfaces 112,114 of teeth 40 cooperate to define parallel annular walls 120,122 extending around central axis 66. Similarly, third side surfaces 116 cooperate to define a cylindrical wall 124 extending around central axis 66. First and second side walls 120,122 and cylindrical wall 124 cooperate to define annular groove

50 as shown in Fig. 6. Each of narrow slits 42 and wide gap 34 extend through first and second parallel annular side walls 120,122 and cylindrical wall 124 as shown in Fig. 6.

Each tooth 40 further includes first and second parallel edges 126,128 that cooperate to define slots 42. According to an alternative embodiment, the first and second edges are non-parallel.

Center portion 46 is recessed relative to left and right frustums 44,48 to define groove 50. As shown in Fig. 6, left frustum 44 includes a left end 130 and a right end 132. As shown in Fig. 8, center portion 46 includes a left end 134 integrally coupled to right end 132 of left frustum 44 and a right end 136. Similarly, right frustum 48 includes a left end 138 integrally coupled to right end 136 of center portion 46 and a right end 140. As shown in Fig. 7, left frustum 44 includes an outer diameter 142 at right end 132 and right frustum 48 includes an outer diameter 144 at left end 138. Center portion 46 includes an outer diameter 146 that is less than outer diameters 144,142 to provide the recess.

As shown in Figs. 6-8, left frustum 44 tapers at a positive slope relative to central axis 66 of approximately 32 degrees. Right frustum 48 tapers at a negative slope relative to central axis 66 of approximately 9 degrees. As shown in Fig. 8, left and right frustums 44,48 and center portion 46 include respective inner surfaces 148,150,152 that cooperate to define inner surface 28. As shown in Fig. 6, left and right frustums 44,48 and center portion 46 include respective wide gaps 154,156,158 extending between respective inner surfaces 148,150,152 and respective outer surfaces 98,110, and cylindrical wall 124. Wide gaps 154,156,158 cooperate to define wide gap 34.

Similarly, each of left and right frustums 44,48 and center portion 46 include a plurality of narrow slits 160,162,164 that are aligned to define narrow slits 42. As shown in Fig.

8, each of narrow slits 160,162,164 includes respective open ends 178,180,182 that cooperate to define open ends 68 of narrow slits 42 and respective closed ends 184,186, 188 that cooperate to define closed ends 70.

Narrow slits 42 extend from left-end surfaces 90 of teeth 40 to right-end surfaces 92 of teeth and have first, second, third, fourth, fifth, sixth, and seventh linear openings 166,168,170,172,174,176,178 defined by adjacent collet teeth 40. First openings 166 are formed in left frustum 44 as shown in Fig. 8. Second, third, and fourth openings 168,170,172 are formed in groove 50 so that second opening 168 faces fourth

opening 172. Fifth openings 174 is formed in right frustum 48. Sixth openings 176 are defined between adjacent right-end surfaces 92 and seventh openings 178 are defined between adjacent left-end surfaces 90 and to face away from respective sixth openings 176 as shown in Fig. 5.

As shown in Fig. 7, wide gap 34 extends from right collet end 38 to left collet end 36 and has first, second, third, fourth, fifth, sixth, seventh and eighth linear openings 180,182,184,186,188,190,192,194 defined by first and second side edges 126,128. First opening 180 is formed in left frustum 44. Second, third, and fourth openings 182,184,186, are formed in groove 50 so that second opening 182 faces fourth opening 186. Fifth opening 188 is formed in right frustum 48. Sixth opening 190 is formed in right collet end 38. Seventh opening 192 is formed in radially inner tool-grip surface 28. Eighth opening 194 is formed in left collet end 36 to face away from sixth opening 190.

As shown in Fig. 5, wide gap 34 has a gap separation angle 198 defined between first and second side edges 127,129 as shown in Fig. 5 to provide clearance between first side edge 127 as second side edge 129 approaches first side edge 127 during circumferentially flexing. According to the present disclosure, gap separation angle 198 falls within a preferred range of about 0.5 degrees for about a 0.002 inch (0.0051 centimeter) gap at the radially inner ends of side edges 126,128 to about 12 degrees for about a 0.0625 inch (0.1118 centimeter) gap. According to alternative embodiments, the wide gap is wider, as wide, or narrower than the narrow slits.

As previously mentioned, a series of collets is provided for different diameter tool shanks and tool holders. Collet body 24 has a length 210 and a width 212 as shown in Fig. 6. A preferred range of widths 212 is provided from about 0.453 inches (1.15 centimeters) to about 2.00 inches (5.04 centimeters). Similarly, a preferred range of lengths is provided from about 0.709 inches (1.08 centimeters) to about 3.00 inches (7.62 centimeters). To accommodate a range of tool shank diameters, a preferred range of inside diameters 30 is also provided to grip tool shanks from about 0.019 inches (0.048 centimeters) to about 1.500 inches (3.81 centimeters).

A kit of collet bodies having incremented inside diameters is also provided. The inside diameters of the collet bodies increase at discrete increments such

as 1/32 inches (0.074 centimeters) or 1 millimeter."Special"collet bodies are also provided having inside diameters between the incremented inside diameters.

To provide adequate flexibility to collet body 24 for the range of gap separation angles 198, C-shaped sleeve 72 is sized to prevent cracking or fatigue. As shown in Fig. 8, C-shaped sleeve 72 has a thickness 214 measured from radially inner tool-grip surface 28 to inner closed ends 70 of narrow slits 42 as shown in Fig. 8.

Thickness 214 of C-shaped sleeve 72 falls with the preferred range of about 0.008 inches (0.020 centimeters) to about 0.100 inches (0.254 centimeters) to provide an adequate range of circular flexibility to collet body 24. The presently preferred thickness is about 0.0625 inches (0.1118 centimeters).

For each specific configuration of collet 16, the depth of narrow slits 42 from open ends 68 to closed ends 70 is different depending on width 212, and inside diameter 30 of radially inner tool-grip surface 28. As inside diameter 30 for a particular set of same-size collet bodies decreases, the depth of narrow slits 42 increase so that a preferred thickness 214 of C-shaped sleeve 72 is maintained for a preferred gap separation angle 198. Similarly, as width 212 for different-sized collet bodies increases, the depth of narrow slits 42 increases to maintain the preferred thickness 214. By maintaining the desired thickness 214 for the desired gap separation angle 198, the desired circular flexibility and gripping characteristics of collet 16 are obtained.

According to alternative embodiment collet bodies, the sleeve thickness may vary between collet bodies sized to grip tool shanks with different diameters or to grip narrower or wider ranges of tool shanks.

As shown in Fig. 5, collet body 24 is formed to include twenty-eight narrow slits 42 having uniform depths and one wide gap 34. Each pair of adjacent narrow slits 42 has a separation angle 216 (preferably 12.4 degrees). According to a presently preferred embodiment, a collet 316 is formed to include sixteen narrow slits 342 as shown in Fig. 10. Collet 316 is otherwise the same as collet 16. According to alternative embodiments of the present invention, a preferred minimum of ten slots narrow slits are provided. The collet bodies may be formed to include as many narrow slits as will fit into the collet body depending on the narrow slit width and the desired sleeve thickness.

According to another alternative embodiment, a collet 416 is formed with a series 426 of alternating"long"and"short"slits 428,430 defining collet teeth 440,442 as shown in Fig. 12. Collet 416 is otherwise identical to collet 16. Collet 416 further includes a C-shaped sleeve 472 coupled to collet teeth 440,442. Series 426 provides collet 416 with additional flexibility without"crowding"the closed ends of the narrow slits too closely to provide a"short"inner arc length. Inner arc lengths that are too short provide a weak tooth-to-sleeve connection. According to alternative embodiments, "medium"and other length slits are also incorporated into the collet body.

Long slits 428 include open ends 468 at outer surface 26 and a closed end 470 terminating short of inner surface 28. Short slits 430 include open ends 474 at outer surface 26 and closed ends 476 terminating short of inner surface 28. Closed ends 470 of long slits 428 are spaced apart from inner surface 28 by a first distance 478 and closed ends 476 of short slits 430 are spaced apart from inner surface 28 by a second distance 480 that is greater than first distance 478.

Thus, a force generator 512 is provided that transmits force through an interrupted transfer surface 526 to an intermediate transfer member 540. This force is then transferred from intermediate transfer member 540 through a continuous grip surface 528 to a work surface 530 as shown diagrammatically in Fig. 12.

Although the invention has been disclosed in detail with reference to certain preferred embodiments, variations and modifications exist within the scope and spirit of the invention.