Patent Application
20060115337
1. Field of the Invention
The invention relates in general to methods and devices for eliminating runout for tools mounted in collet chucks. More particularly, embodiments of the present invention relate to eliminating runout in conventional collet chucks wherein adjustments to the concentricity of tools are applied directly to the tool.
2. Description of the Prior Art
The term “runout” as used in the machine tool arts typically refers to the fact that rotating tools such as drill bits, reamers, end mills, or the like, often do not rotate exactly about their longitudinal axes. That is, the axis of rotation of the tool is not concentric with the longitudinal axis of the tool, at least at the location where the tool engages a workpiece. The cutting tip of the rotating tool, for example, describes a circle rather than a single point because the tool is not centered in its holder (lateral offset), or is mounted in the holder at an angle to the rotational axis of the system, or suffers from some combination of these conditions. This results in inaccurately formed workpieces, and possible damage to the tool or machine. Many prior expedients had been proposed for the purpose of minimizing or eliminating runout. The prior art devices and methods are not without their shortcomings. A major shortcoming of typical prior art devices and methods is their complexity in both construction and use. Further, such prior expedients did not apply adjustments to the concentricity of the mounting of a tool directly to the tool itself. For example, Priessnitz U.S. Pat. No. 4,930,957 proposes to center a tool restrained within a collet by forming the driver for the holder of the collet so that it can be deflected by adjustment screws mounted in the driver. This is problematic for a number of reasons. This distortion of the driver deflects the holder for the collet, the collet itself, and the tool that is chucked in the collet. While the tip of the cutting tool may be rotating about a single point after the adjustment is made, the rest of the rotating mass is frequently not rotating concentrically with the longitudinal axis of the system. At higher speeds there is enough unbalanced rotating mass to generate substantial vibration. Such modifications to the driver are expensive, require precise modifications, and tend to weaken it. If more than four adjustment screws are required, they would be difficult or impossible to provide. Some proposed prior expedients required that a skilled machinist first correct the angular misalignment of the tool and then the lateral offset of the tool. This takes time and requires considerable skill and experience. Many prior proposed expedients were subject to rapid wear or were easily damaged.
Prior expedients for aligning tools that are not mounted in collets include, for example, Micek U.S. Pat. No. 4,666,353 (adjusting the driver to which a holder for a tool is mounted); Jacobson U.S. Pat. No. 4,930,947 (a tool holder wherein a tool is secured in a bore by a radially mounted set screw, and the tool is purportedly centered to the tool holder by a pair of alignment members that extend tangentially of the bore); McGill U.S. Pat. No. 4,326,361 (an adjustable hub mount for a circular saw blade where four adjustment screws cause the hub to be mis-aligned to compensate for lateral warpage of the saw blade); Stelmachowski U.S. Pat. No. 2,841,929 (Uses circumferentially spaced set screws acting radially on the hub for a diamond grinding wheel to shift the hub and wheel radially of the axis of rotation to bring the axis of rotation of the system into congruency with the axis of the wheel); and Hoffman U.S. Pat. No. 4,265,057 (a shaft to which a chuck for a gem stone is mounted is inserted into a tubular dop arm and aligned with the axis of the dop arm by two sets of four screws each where the sets of screws are axially spaced along tubular dop arm). The assembly of Hoffman is only rotated in small precise angular increments to accomplish the cutting of facets on a gem stone. The assembly holds the workpiece rather than the tool. A lath dog in the form of a stepped cylindrical sleeve that is fastened to both a tool and a tool holder was proposed by Ingram U.S. Pat. No. 3,691,883. The set screws that secure the assembly together are not positioned so as to accomplish precision alignment of the cutting tool. The purpose is to prevent rotation of the tool in the holder, not to accomplish precision alignment of the tool.
Those concerned with these problems recognize the need for an improved precision tool alignment assembly, particularly where the runout is in the range of about b 0.002 inches or less, and a collet chuck assembly is employed.
The present invention has been developed in response to the current state of the art, and in particular, in response to these and other problems and needs that have not been fully or completely solved by currently available expedients. Thus, it is an overall object of the present invention to effectively resolve at least the problems and shortcomings identified herein. In particular, it is an object of the present invention to provide a simple, rugged precision alignment assembly for rotating tools wherein an aligning force is applied directly to a tool mounted in a collet chuck. It is also an object of the present invention to provide according to one embodiment an alignment assembly that can be mounted to a conventional collet chuck assembly without modifying the conventional collet chuck assembly. Finally, it is an object of the present invention to provide an alignment assembly that can be used by relatively unskilled workers to quickly adjust at least the alignment of the tip of a rotating cutting tool to be congruent or in a predetermined relationship with the rotational axis of the system. Embodiments of the present invention are particularly suitable for correcting small radial excursions (less than about 0.002 inches) of the tip of a rotating cutting tool
A preferred embodiment of the precision alignment assembly according to the present invention comprises a collet chuck assembly that includes a conventional collet member and a clamping nut element. The clamping nut element is threadably mounted to a conventional tool holder. When the clamping nut is tightened it squeezes the collet member radially inwardly to grip a shank of a tool that is received axially in the collet member. The collet chuck assembly has an axis of rotation about which it rotates. The tool has a longitudinal axis and a tip. The tool projects axially from the axially outer end of the collet, and the tip is axially remote from the shank.
A precision collet chuck assembly according to the present invention includes at least three generally radially adjustable elements spaced generally circumferentially from one another around the axis of rotation of the assembly. These radially adjustable elements are positioned to bear directly on the tool generally along radii of the tool or the assembly. Tools frequently have generally cylindrical forms, however, other cross-sectional forms such as square, hexagonal, or the like are sometimes used. Regardless of the cross-sectional shape of the tool, it generally has a longitudinal axis. The radially adjustable elements apply force generally along radii of the tool relative to the axis of rotation of the system. The location of the tool tip is adjusted relative to the axis of rotation of the system by adjustment of the adjustable elements. These radially adjustable elements are in adjustably engaging relationship with the tool at a location between the tool shank in the collet member and the tip.
The generally radially adjustable elements are preferably threadably mounted for ease of radial adjustment. These elements can be mounted, for example, in the clamping nut element, or in a centering collar member. The centering collar member is preferably mounted at least in part to the clamping nut element. One form of centering collar is a centering bonnet that slips over and clamps to a conventional clamping nut element. In general, at least three radially adjustable elements are provided. More radially adjustable elements can be employed, if desired. Four, five, six, or more such elements can be employed.
The generally radially adjustable elements function by deflecting the tool to bring the longitudinal axis of the tool into a desired alignment with the axis of rotation of the system, at least at approximately the tip of the tool. Usually, the objective is to bring the tip of the tool into alignment with the rotational axis of the system so that the tip rotates about a single point rather than defining a circle as it rotates. In some circumstances, it is desirable that the tool tip describe such a circle. The present invention is adapted to adjusting the tool to obtain either objective.
The generally radially adjustable elements bear directly on the tool at a location between the shank in the collet member and the tip of the tool, and are subject to considerable shock and vibration. Preferably, these elements are positioned radially to bring the tool into the desired alignment with the rotational axis of the system and then locked into these desired radial positions. To this end, locking members are provided in locking association with these radially adjustable elements. In one embodiment these locking members take the form of set screws that laterally engage, through protective pads, the radially adjustable elements.
To acquaint persons skilled in the pertinent arts most closely related to the present invention, a preferred embodiment of a precision alignment assembly that illustrates a best mode now contemplated for putting the invention into practice is described herein by, and with reference to, the annexed drawings that form a part of the specification. The exemplary precision alignment assembly is described in detail without attempting to show all of the various forms and modifications in which the invention might be embodied. As such, the embodiments shown and described herein are illustrative, and as will become apparent to those skilled in the arts, can be modified in numerous ways within the scope and spirit of the invention, the invention being measured by the appended claims and not by the details of the specification or drawings.
Other objects, advantages, and novel features of the present invention will become more fully apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings, or may be learned by the practice of the invention as set forth herein.
The present invention provides its benefits across a broad spectrum of machining operations. While the description which follows hereinafter is meant to be representative of a number of such applications, it is not exhaustive. As those skilled in the art will recognize, the basic apparatus taught herein can be readily adapted to many uses. This specification and the claims appended hereto should be accorded a breadth in keeping with the scope and spirit of the invention being disclosed despite what might appear to be limiting language imposed by the requirements of referring to the specific examples disclosed.
Referring particularly to the drawings for the purposes of illustrating the invention and its presently understood best mode only and not limitation:
Referring now to the drawings wherein, like reference numerals designate identical or corresponding parts throughout the several views. It is to be understood that the drawings are diagrammatic and schematic representations of various embodiments of the invention, and are not to be construed as limiting the invention in any way. The use of words and phrases herein with reference to specific embodiments is not intended to limit the meanings of such words and phrases to those specific embodiments. Words and phrases herein are intended to have their ordinary meanings, unless a specific definition is set forth at length herein.
Referring particularly to the
With particular reference to
The rotational axis of the assembly is located at 37. The radially inner ends of set screws 38, 40, and 42 are located in substantially the same adjustment circle on the surface of the tool. This adjustment circle is generally centered on rotational axis 37, and is generally approximately concentric with and spaced axially outwardly from the bore of the collet member. These set screws are spaced approximately equally around this adjustment circle, and project generally radially towards rotational axis 37. When the axes of the set screws define a plane, the ends of the set screws meet the surface of the tool at about 90 degrees. If desired, the adjusting elements can be mounted so that their longitudinal axes define one or more cones with the tip of the cones generally centered on the rotational axis of the assembly. This permits the radial adjusting force to be applied at a contact angle of other than 90 degrees to the surface of the tool. The radially inner ends of the set screws can be shaped to provide a line of contact or a point contact between the surface of the tool and the ends of the adjusting elements. Also, the force applied can be in the nature of a wedging action when the longitudinal axis of the set screw extends at an angle to the axis of rotation. This is desirable in some circumstances. Angles of as much as 60 degrees or more can be employed, if desired. A combination of conical and planer mounting forms can be employed for the adjusting set screws, if desired, particularly if more than four set screws are used in a set.
Set screws 38, 40, and 42 are shown for purposes of illustration as projecting radially outwardly from the outer circumference of body 46. The radially adjustable elements typically do not project beyond the outer circumference of the body 46 in use. This is for reasons of safety and balance, and to avoid interference with the engagement of a spanner in slots 34 for the purpose of threadably rotating the clamping nut. The ends 44 of the radially adjustable set screws are preferably slightly concave to provide a better engagement with the shank of a tool received in bore 15.
Because the radially adjustable element preferably bear directly against the surface of a cutting tool at a location axially outwardly from the shank portion that is gripped in the collet member, they are subject to substantial shock and vibration. To lock them in a desired radial position they are preferably associated with locking elements. An embodiment of a locking element is illustrated in
In use, set screw 40 is threadably adjusted to bring the cutting tool into a desired alignment with the rotational axis 37 of the collet chuck assembly. The locking set screw 48 is threadably advanced to jam the thread protecting pad 52 into the thread of the radially adjustable set screw 40. This prevents the set screw 40 from rotating. Set screw 40 is released by backing off the locking set screw 48 so that the force on the thread protecting pad 52 is released.
With particular reference to
Set screws provide a convenient form of radially adjustable elements because threaded bores to receive them can be formed quickly, easily, and accurately in separate centering collar members and in centering collar members that are a part of a clamping nut element. Set screws are very simple and reliable, and function with a minimum number of parts and mounting operations.
Other forms of radially adjustable elements can be employed according to the present invention, if desired. For example, wedging elements can be incrementally and selectively forced into engagement with a tool shank. Generally, such wedging elements are slidably mounted in a channel or groove in the centering collar member and are incrementally advanced or withdrawn under the urging of a threaded element. Other like radially adjustable elements can be employed if desired. Likewise, locking set screws are conveniently used because it is easy and simple to mount them, and they are very reliable. Other locking systems can be employed, if desired. For example, self locking nuts or inserts of various designs can be used. Also, jam screws, jam nuts, or the like can be employed.
The radially adjustable elements are typically arranged in generally equally spaced circumferential arrays around the rotational axis of a collet chuck assembly. The individual elements in a set of such elements are independently adjustable, and each set includes at least three individual elements. The elements bear on a tool at a location between the tip of the tool and the axially outer end of the collet member. The shank portion of the tool is received in the collet. For purposes of this patent it is intended that the shank be considered to be that part of the tool that is axially rearward of the axially outer end of the collet. Any part of the tool that projects axially outwardly of the collet is not considered to be part of the shank. Preferably, the elements are arrayed around approximately a common adjusting circle centered on the rotational axis of the assembly. It has been found that by locating this adjusting circle between the tip of the tool and the axially outer end of the collet member the desired precision adjustment can be achieved. It is generally not necessary to locate individual elements of the adjusting array axially of one another along the axis of rotation. Such axial location of adjusting elements substantially increases the length and complexity of the centering collar member, the time and degree of skill required to achieve the desired adjustment, and the cost of the assembly.
Selective adjustment of the adjusting elements causes the tip of the tool to be deflected slightly towards a desired alignment with the axis of rotation of the collet chuck assembly. Since the tool is generally first clamped into the assembly by fully tightening the clamping nut, the amount that the tip can be deflected is relatively small, typically less than about 0.002 inches. This is sufficient for many precision machining operations.
Many different forms of collet chuck assemblies are commercially available. The present invention is generally applicable for use with all of them. The location of the adjusting circle between the tip of the tool and the axially outer end of the collet removes the adjusting elements and associated members from interference with the collet and clamping nut, regardless of their forms. In general, a centering collar, whether integral with a clamping nut or separate from the nut, should be configured to mate closely with the particular form of collet-nut assembly to which it is to be applied.
With particular reference to
With particular reference to
With particular reference to
With particular reference to
What have been described are preferred embodiments in which modifications and changes may be made without departing from the spirit and scope of the accompanying claims. Many modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.
