Spindle assemblies comprising an outer casing and a tool spindle rotatably mounted within the casing are known in the prior art. The spindle supports a tool, such as a milling or other cutting tool. The assembly may comprise an internal motor for effecting rotation of the tool spindle and, hence, the tool. The outer casing is typically mounted in a main housing. In one know implementation, the outer casing is bolted to the main housing at a location near the tool supported by the spindle. Hence, a rear portion of the casing is cantilevered relative to the main housing. In such an implementation, for a given tool size and tool operating speed, the tool can only move relative to the workpiece to effect cutting or a like operation up to a certain maximum speed before the spindle assembly/main housing apparatus becomes unstable as the result of excessive vibration. That is, once the work speed exceeds a certain threshold, the amount of energy input into the spindle assembly/main housing apparatus unacceptably exceeds that which is being removed by one or more damping systems incorporated into the spindle assembly/main housing apparatus. One particular mode of vibration which causes the spindle assembly/main housing apparatus to become unstable is cantilever vibration, whereby the rear portion of the casing transversely oscillates an excessive amount relative to the main housing. Accordingly, there is a need for an improved damping system which is capable of substantially reducing if not eliminating this mode of vibration.

SUMMARY OF THE INVENTION This need is met by the present invention whereby an improved spindle assembly and main housing are provided such that vibration occurring at an outer casing relative to a main housing is minimized.

In accordance with a first aspect of the present invention, a spindle assembly/main housing apparatus is provided. It comprises a spindle assembly including an outer casing and a tool spindle rotatably mounted within the outer casing. The tool spindle has a first tool

supporting end and a second end opposite the first end. The outer casing has first and second ends. At least one first O-ring is positioned about the second end of the outer casing. A main housing is further provided and has a central bore in which the outer casing is housed. One or more connectors couple the outer casing first end to the main housing. A first section of the outer casing adjacent to the first O-ring defines a first gap with a first section of the main housing opposing the outer casing first section. The at least one first O-ring has a sufficient diameter and a sufficient material stiffness and the gap has a sufficient width to attenuate a substantial amount of vibration occurring at the outer casing second end relative to the main housing.

The spindle assembly/main housing apparatus may further comprise at least one second O-ring positioned about the first end of the outer casing. A second section of the outer casing adjacent to the second O-ring defines a second gap with a second section of the main housing opposing the outer casing second section. The second O-ring has a sufficient diameter and a sufficient material stiffness and the second gap has a sufficient size to further attenuate a significant amount of vibration occurring at the outer casing second end relative to the main housing.

Preferably, a closed damping chamber is defined between one of the first O-rings, one of the second O-rings, an outer intermediate section of the outer casing and an inner intermediate section of the main housing. A fluid is provided in the closed damping chamber. The fluid is preferably selected from the group consisting of water, ethylene glycol, and combinations thereof.

In a first embodiment, the outer intermediate section of the outer casing comprises a first outer cylindrical portion and a second outer portion. The second outer portion extends out from the first outer portion and defines a raised helix. The inner intermediate section of the main housing defines a generally cylindrical inner portion. The second outer portion defines a third gap with the inner portion.

Preferably, the helix defines an angle with a plane orthogonal to a longitudinal axis of the outer casing.

The first and second outer portions of the outer intermediate section of the outer casing and the inner portion of the inner intermediate section of the main housing define a generally helical cooling chamber.

In a second embodiment, the outer intermediate section of the outer casing defines a

generally cylindrical outer portion, the inner intermediate section of the main housing defines a generally cylindrical inner portion, and the generally cylindrical outer portion defines a third gap with the generally cylindrical inner portion.

The first end of the outer casing may comprise a flange.

In accordance with a second aspect of the present invention, a spindle assembly/main housing apparatus is provided. It comprises a spindle assembly comprising an outer casing and a tool spindle rotatably mounted within the outer casing. The tool spindle has a first tool supporting end and a second end opposite the first end. The outer casing has first and second ends. At least one first O-ring is positioned about the second end of the outer casing and at least one second O-ring is positioned about the first end of the outer casing. A main housing is also provided and has a central bore in which the outer casing is housed. One or more connectors couple the outer casing first end to the main housing. A closed damping chamber is defined between one of the first O-rings, one of the second O-rings, an outer intermediate section of the outer casing and an inner intermediate section of the main housing. A fluid is provided in the damping chamber and acts to attenuate a significant amount of vibration occurring at the outer casing second end relative to the main housing.

In accordance with a first embodiment of the present invention, the outer intermediate section of the outer casing comprises a first outer cylindrical portion and a second outer portion. The second portion extends from the first outer portion so as to define a raised helix.

The inner intermediate section of the main housing defines a generally cylindrical inner portion. The second outer portion defines a third gap with the inner portion.

The first and second outer portions of the outer intermediate section of the outer casing and the inner portion of the inner intermediate section of the main housing define a generally helical cooling chamber.

In accordance with a second embodiment of the present invention, the outer intermediate section of the outer casing defines a generally cylindrical outer portion, the inner intermediate section of the main housing defines a generally cylindrical inner portion, and the generally cylindrical outer portion defines a third gap with the generally cylindrical inner portion.

In accordance with a third aspect of the present invention, a spindle assembly/main housing apparatus is provided. It comprises a spindle assembly comprising an outer casing and a tool spindle rotatably mounted within the outer casing. The tool spindle has a first tool

supporting end and a second end opposite the first end. The outer casing has first and second ends. At least one first O-ring is positioned about the second end of the outer casing. A main housing is provided and has a central bore in which the outer casing is housed. A first section of the outer casing adjacent to the first O-ring defines a first gap with a first section of the main housing opposing the outer casing first section. One or more connectors couple the outer casing first end to the main housing. The at least one first O-ring is made of a material and sized relative to the gap so that a substantial amount of vibration occurring at the outer casing second end relative to the main housing is attenuated.

In accordance with a fourth aspect of the present invention, a spindle assembly is provided which is adapted to be received within a central bore in a main housing. The assembly comprises an outer casing and a tool spindle rotatably mounted within the outer casing. The tool spindle has a first tool supporting end and a second end opposite the first end. The outer casing has first and second ends. At least one first O-ring is positioned about the second end of the outer casing. A first section of the outer casing adjacent to the first O- ring defines a first gap with a first section of the main housing opposing the outer casing first section. One or more connectors couple the outer casing first end to the main housing. At least one first O-ring has a sufficient diameter and a sufficient material stiffness and the gap has a sufficient width to attenuate a substantial amount of vibration occurring at the outer casing second end relative to the main housing.

BRIEF DESCRIPTION OF THE DRAWINGS A better understanding of the present invention will be had upon reference to the following description in conjunction with the accompanying drawings in which like numerals refer to like parts, and wherein: Fig. 1 is a view, partially in cross section, of a spindle assembly/main housing apparatus constructed in accordance with a first embodiment of the present invention; Fig. 2 is an enlarged view, partially in cross section, of the apparatus portion within the area designated Fig. 2 in Fig. 1; Fig. 3 is an enlarged view, in cross section, which is similar to Fig. 2 but without a fluid between the spindle casing and the main housing; Fig. 4 is an enlarged view, partially in cross section, of the apparatus portion within the area designated Fig. 4 in Fig. 1;

Fig. 5 is an enlarged view, partially in cross section, of the apparatus portion within the area designated Fig. 5 in Fig. 1; Fig. 6 is a view, partially in cross section, of a spindle assembly/main housing apparatus constructed in accordance with a second embodiment of the present invention; and Fig. 7 is a view, partially in cross section, of the apparatus portion within the area designated Fig. 7 in Fig. 6.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawings, Fig. 1 illustrates a spindle assembly/main housing apparatus 10 constructed in accordance with a first embodiment of the present invention. It comprises a spindle assembly 20 including an outer casing 22 and a tool spindle 24 rotatably mounted within the outer casing 22. The outer casing has a first end 22a and a second end 22b. The tool spindle 24 has a first tool supporting end 24a and a second end (not shown) opposite the first end. The structure provided within the outer casing 22 is conventional and may comprise a motor (not shown) for effecting rotation of the tool spindle 24 relative to the outer casing 22. However, it is contemplated that the drive apparatus for rotating the spindle 24 may be provided outside the casing 22.

The apparatus 10 further comprises a main housing 30 having a central bore 31 in which the outer casing 22 is mounted. It further has first and second ends 30a and 30b. The outer casing 22 includes a flange 26 which is located at the first end 22a of the casing 22.

One or more connectors, such as bolts 40, couple the flange 26 to the first end 30a of the main housing 30. As is illustrated in Fig. 1, due to this coupling arrangement, the second end 22b of the outer casing 22 is cantilevered relative to the main housing 30.

A cutting tool (not shown) may be coupled to the first end 24a of the spindle 24. In the illustrated embodiment, the outer casing 22 has a length LC, see Figs. 1 and 3. The main housing 30 has a length LH and an inner diameter DH.

The present invention provides first and second damping systems 50 and 60 which reduce or attenuate a significant amount of cantilever vibration, i. e. , transverse oscillatory movement of the second end 22b of the casing 22 relative to the second end 30b of the main housing 30. By reducing this mode of vibration, the rate at which the cutting tool held by the spindle 24 may be moved into a workpiece and/or the rate at which a workpiece may be moved toward the cutting tool can be increased before the apparatus 10 becomes unstable due

to unacceptable vibration. That is, the damping systems of the present invention attenuate an increased amount of vibrational energy such that the apparatus 10 is capable of receiving a higher amount of energy during a cutting operation before becoming unstable.

The first damping system 50 comprises a first O-ring 52 positioned about the second end 22b of the outer casing 22, see also Fig. 5, a second O-ring 54 positioned about the first end 22a of the outer casing 22, see also Fig. 4, and a third O-ring 56 also provided about the first end 22a of the outer casing 22. First sections 22c of the outer casing 22 adjacent to the first O-ring 52 define first gaps Gl with a first section 30c of the main housing 30 opposing the outer casing first sections 22c. Second sections 22d of the outer casing 20 adjacent to the second O-ring 54 define second gaps G2 with a second section 30d of the main housing 30 opposing the outer casing second sections 22d. Third sections 22e of the outer casing 2 adjacent to the third O-ring 56 define third gaps G3 with a third section 30e of the main housing 30 opposing the outer casing third sections 22e.

In the illustrated embodiment, each of the first, second and third 0-rings 52,54 and 56 has a diameter D1, D2, D3. Further, the 0-rings 52,54 and 56 are formed from a polymeric material. Each of the gaps G1, G2, G3 has a size or height H. This damping system 50, having the dimensions and material stiffness set out above, and when incorporated into an apparatus 10 having the spindle assembly and main housing dimensions noted above, is capable of attenuating a significant amount of vibration occurring at the outer casing second end 22b relative to the main housing 30. It is believed that the first O-ring 52 dissipates a majority of the vibration attenuated by the first damping system 50.

The second damping system 60 comprises a closed damping chamber 62 defined between the first and second 0-rings 52 and 54, an outer intermediate section 22f of the outer casing 22 and an inner intermediate section 30f of the main housing 30, see Figs. 1 and 2.

The outer intermediate section 22f of the outer casing 22 comprises a first outer cylindrical portion 22g and a second outer portion 22h. The second outer portion 22h extends out from the first outer portion 22g and defines a raised helix 26. The helix 26 preferably forms an angle _ with a plane P1 orthogonal to a longitudinal axis of the outer casing 20. The inner intermediate section 30f of the main housing 30 defines a generally cylindrical inner portion 300. As is apparent from Fig. 1, the closed damping chamber 62, which is defined by the first and second outer portions 22g and 22h of the outer intermediate section 22f and the inner portion 300 of said inner intermediate section 30f, comprises a generally helical cooling

chamber C. A fluid F circulates through the helical cooling chamber C to effect cooling of the outer casing 22. It further functions to dissipate vibrational energy, as will be discussed further below.

An outer edge 26a of the helix 26 defines a plurality of gaps G4 with the inner intermediate section 30f of the main housing 30 portion, see Figs. 2 and 3. The gaps G4 preferably have a size or height HG. The gaps G4 define squeeze-film chambers which receive fluid F circulating through the cooling chamber C. Movement of the fluid into and out of the gaps G4 results in damping of a portion of the transverse oscillatory movement of the outer casing 20 relative to the main housing 30.

The fluid F is input into a first bore 32 of the main housing 30 via a conventional input structure (not shown) coupled to the housing 30. After circulating through the helical cooling chamber C, it passes through first and second openings 28a and 28b in the outer casing 22 and flows out of the apparatus 10 through a second bore 34 in the main housing 30.

A conventional output structure is coupled to the housing 30 for carrying the fluid away from the apparatus 10. A flange is coupled between the openings 28a and 28b and is positioned within the casing 20 for carrying the fluid from the first opening 28a to the second opening 28b. The fluid F may comprise water, ethylene glycol and combinations thereof.

An apparatus 100 constructed in accordance with a second embodiment of the present invention is illustrated in Figs. 6 and 7, where like elements are referenced by like reference numerals. The apparatus 100 includes the same first damping system 50 provided in the apparatus 10, illustrated in Figs. 1-5. However, the second damping system 600 is constructed in a different manner.

The second damping system 600 includes a closed damping chamber 620 defined between the first and second 0-rings 52 and 56, an outer intermediate section 220f of the outer casing 220 and an inner intermediate section 30f of the main housing 30, see Figs. 1 and 7. The outer intermediate section 220f of the outer casing 220 defines a generally cylindrical outer portion 230, and the inner intermediate section 30f of the main housing 30 defines a generally cylindrical inner portion 300. The cylindrical outer portion 300 defines a gap G5 with the cylindrical inner portion 230. The gap G5 preferably has a size or height HG2. The gap G5 defines a squeeze-film chamber which receives fluid F. Movement of the fluid into and out of the gap G5 results in transverse oscillatory movement of the outer casing 20 relative to the main housing 30 being further attenuated.

The fluid F enters into the closed damping chamber 620 through bore 32 and exits the chamber through opening 28a. The fluid F then passes through opening 28b before leaving the apparatus 100 through bore 34.

While the invention has been illustrated with reference to one or more preferred embodiments hereof, and such preferred embodiments have been described in considerable detail with reference to the drawings, it is not the intention of applicants that the invention be restricted to such detail.