Arbor Assembly

This invention relates generally, as indicated, to an arbor assembly, and more particularly to an arbor assembly which greatly facilites concentrically locating and clamping a workpiece on a spindle center of a machine tool and subsequent removal therefrom.

Before a workpiece can be accurately machined on a machine tool, the workpiece must be concentrically oriented and securely clamped with respect to the spindle center of the machine tool. Various arbor and/or chuck assemblies have been designed for this purpose which have been met with varying degrees of success. However, there is a continuing need for a more effective way of concentrically locating a workpiece with respect to the spindle center. Also, there is a continuing need for a more effective way of applying a clamping force to the workpiece to maintain the workpiece in such concentric position without placing undue stresses on the clamping mechanism and still provide for easy assembly and disassembly of the workpiece from the arbor assembly.

In accordance with one aspect of the present invention, there is provided an arbor assembly including a fixed arbor section which may already be set up on the spindle center of a machine tool and a removable arbor section. Each arbor section includes two longitudinally spaced apart cylindrical pilot surfaces spaced the same distance apart so that the pilot surfaces on each arbor section will start to engage and disengage each other at the same time during assembly and disassembly of the removable arbor section with respect to the fixed arbor section.

In accordance with another aspect of the invention, a guiding taper is desirably provided between the pilot surfaces on each arbor section to aid in aligning such pilot surfaces so that they freely engage each other during assembly. Such guiding taper and pilot surfaces can be assembled very easily, which is particularly important where, as is the usual case, the loader that places the removable arbor section on the fixed arbor section has low positioning accuracy requiring the arbor assembly to assemble and disassemble as freely as possible.

Also in accordance with the invention, both arbor sections are desirably provided with opposed external locating tapers engageable by spaced apart internal tapered bearing surfaces on the workpiece for clamping of the workpiece between such arbor sections.

In accordance with another aspect of the invention, a floating collet is desirably provided for gripping the inner diameter of the removable arbor section and transmitting a clamping force thereto to force the removable arbor section toward the fixed arbor section to clamp the workpiece securely between such arbor sections, leaving a slight clearance space between the two guiding tapers on the arbor sections so as not to interfere with such clamping action.

In accordance with still another aspect of the invention, a spring cartridge is desirably used to apply the clamping force to the collet while the collet is in a free state without any flexing of the collet fingers.

Also in accordance with the invention, only when the clamping force is released are the collet fingers free to flex inwardly to permit the removable arbor section and workpiece to be assembled onto and removed from the fixed arbor section.

In accordance with yet another aspect of the invention, the inner end of the collet is desirably supported by a collet supporting spring so that the collet can float when a clamping force is applied thereto further to prevent any bending or flexing loads from being applied to the collet during clamping.

Also in accordance with the invention, a lost motion connection is desirably provided between the collet and fixed arbor section to prevent removal of the collet during removal of the removable arbor section and workpiece from the fixed arbor section.

To the accomplishment of the foregoing and related ends, the invention, then, comprises the features hereinafter fully described and particularly pointed out in the claims, the following description and the annexed drawings setting forth in detail a certain illustrative embodiment of the invention, this being indicative, however, of but one of the various ways in which the principles of the invention may be employed.

FIG. 1 is a fragmentary longitudinal section through a preferred form of arbor assembly in accordance with this invention shown in the unclamped position;

FIG. 2 is a fragmentary longitudinal section similar to FIG. 1 but showing the arbor assembly in the clamped position; and

FIG. 3 and 4 are enlarged longitudinal sectional views of portions of the arbor assemblies of FIGS. 1 and 2, respectively.

Referring now in detail to the drawings, and initially to FIGS. 1 and 2, there is shown a preferred form of arbor assembly 1 in accordance with this invention including a fixed arbor section 2 and a removable arbor section 3 receivable over the upper end of the fixed arbor section 2 in concentric relationship therewith for clamping of a workpiece W between such arbor sections 2, 3. FIG. 1 and the FIG. 3 enlargement show the arbor assembly in the unclamped position, whereas Fig. 2 and the FIG. 4 enlargement show the arbor assembly in the clamped position.

The fixed arbor section 2 may be bolted or otherwise secured to the upper face 4 of a compensating chuck 5 which is in turn suitably secured to a spindle of a machine tool used to machine the workpiece W. The fixed arbor section 2 and compensating chuck 5 are desirably located on the spindle center of the machine tool. Accordingly, by using the removable arbor section 3 to concentrically locate the workpiece W on the fixed arbor section 2 as described hereafter, the workpiece W will also be concentrically located on the spindle center.

Preferably, the removable arbor section 3 is concentrically located with respect to the fixed arbor section 2 by means of two matching sets of longitudinally spaced apart internal and external cylindrical pilot surfaces 7, 8 and 9, 10 which may but need not be of different diameters on the respective arbor sections 2, 3. Moreover, such pilot surfaces 7, 8 and 9, 10 on the respective arbor sections 2, 3 are desirably spaced the same distance apart so that the pilot surfaces on each arbor section will commence engaging and disengaging each other at the same time to assist the removable arbor section 3 in sliding freely on and off the fixed arbor section 2 for ease of assembly and disassembly of such arbor sections. Between the respective pilot surfaces 7, 8 and 9, 10 on each arbor section 2, 3 are guiding tapers 11 and 12 which aid in aligning the pilot surfaces during such assembly. Such guiding tapers and pilot surfaces can be assembled very easily, which is especially important in applications where, as is the usual case, the workpiece W and removable arbor section 3 are handled by a loader and unloader which are not very accurate in their positioning and removal functions.

After the removable arbor section 3 has moved downwardly to clamp the workpiece W securely between the two arbor sections as illustrated in FIGS. 2 and 4, there is still a slight clearance taper (space) 15 between the two guiding tapers 11, 12 so as not to interfere with such clamping action.

The workpiece W must of course also be concentrically located with respect to the arbor sections 2, 3. To that end, both arbor sections 2, 3 are desirably provided with opposed, longitudinally spaced external locating tapers 17, 18. Also, the workpiece (in this case a drum) W has a stepped internal bore 19 therethrough with spaced apart tapered internal bearing surfaces 20, 21 that desirably closely match the respective external locating tapers 17, 18 on the arbor sections 2, 3 to support and clamp the workpiece W therebetween.

The required clamping force is transmitted to the removable arbor section 3 utilizing a floating collet 23 which has a collet sleeve 24 received within the axial outer end of the fixed arbor section 2 and extending axially outwardly therefrom with a plurality of circumferentially spaced collet fingers 25 extending radially outwardly from the protruding end thereof for receipt in an internal counterbore 26 within the removable arbor section 3 axially inwardly of the two internal pilot surfaces 9, 10 thereon.

Collet 23 is desirably free to float relative to the fixed arbor section 2 but may be retained against removal therefrom by means of a lost motion connection 28 therebetween. In the preferred embodiment disclosed herein, such lost motion connection 28 is formed by providing an external annular groove 29 in the collet sleeve 24 and one or more stop screws 30 extending radially through the fixed arbor section 2 into such groove. The axial length of the groove 29 is sufficiently greater than the outer diameter of the inner ends 31 of the stop screws 30 which are received in the groove 29 to permit a desired range of movement of the collet 23 relative to the fixed arbor section 2 while still preventing removal therefrom.

Preferably, collet 23 is supported within fixed arbor section 2 by a compression spring 32 interposed between the axial inner end of the collet sleeve 23 and an internal shoulder 33 in the fixed arbor section so that the collet 23 can float when a clamping force is applied to the collet to prevent any bending or flexing loads from being applied to the collet during clamping. The lost motion connection 28 will of course keep the collet 23 from popping out of the fixed arbor section 2 when the removable arbor section 3 and workpiece W are removed from the fixed arbor section 2.

The desired clamping forces may be transmitted to the collet fingers 25 by means of an actuating shaft 35 which extends coaxially through the center of the collet 23 and fixed arbor section 2. At the axial outer end of the actuating shaft 35 is an enlarged, tapered head portion 36 which partially radially overlaps the collet fingers 25. When the actuator shaft 35 is in it fully extended (raised) position shown in FIGS. 1 and 3, there is a clearance space 37 between the enlarged head portion 36 and collet fingers 25, whereby the collet fingers 25 are free to flex inwardly to permit the removable arbor section 3 to be freely inserted over the fixed arbor section 2 and removed therefrom. During such assembly and disassembly, there are no clamping forces to contend with. Accordingly, very little stress is applied to the collet fingers 25 during such assembly and disassembly.

After the removable arbor section 3 and workpiece W have been assembled onto the fixed arbor section 2, the enlarged head portion 36 of the actuating shaft 35 may be moved axially inwardly (downwardly) from the FIG. 1 (or 3) position to the FIG. 2 (or 4) position into engagement with the collet fingers 25 to trap the collet fingers 25 between the inner diameter (I.D.)of the removable arbor section 3 and enlarged head portion 36. Continued axial inward (downward) movement of the actuating shaft 35 causes the collet fingers 25 to apply an axial clamping force against an internal shoulder 38 on the removable arbor section 3 to clamp the workpiece W between the two arbor sections 2, 3 when the removable arbor section 3 is moved into the clamping position shown in FIG. 2 and 4 without any flexing of the collet fingers 25. Since there are no bending (flexing) loads applied to the collet 23 during clamping of the workpiece W between the arbor sections 2, 3, the useful life of the collet 23 is greatly increased. Only when the clamping pressure exerted by the enlarged head portion 36 of the actuating rod 35 is released are the collet fingers 25 free to flex inwardly to permit the removable arbor section 3 to be removed (and inserted over) the fixed arbor section 2. However, during this phase, there are no clamping forces to contend with.

The actual clamping force is desirably provided by a disc-spring cartridge 40 which, as shown, consists of a stack of spring-discs 41 slidably received on an acutating rod 42 having a threaded or other suitable connection 44 with actuating shaft 35. The disc-springs 41 may be retained on the actuating rod 42 by means of a nut 45 threaded onto the inner (lower) end of the rod 42 and secured in place as by means of a dowel pin 46 extending through the nut 45 and rod 42. At the outer (upper) end of the disc-spring cartridge 40 is a spacer 47 which may have suitable passages 48 therethrough to provide for an air blow-off of the arbor components to maintain cleanliness. The arbor assembly operates in a highly contaminated environment where cast iron machining is being performed. Any cast iron dust and chips entering the arbor assembly would degrade its accuracy in locating a workpiece, thus the need for air blow-off. Also, the blow-off air is desirably lubricated air which coats the internal arbor components with a film of lubricating oil insuring free operation. Also, a compressible foam seal 49 or the like may be attached to the removable arbor section 3 to provide for sealed engagement with the outer (upper) end of the fixed arbor section 2 as a further aid in keeping out cutting chips and the like.

The clamping force exerted on the collet 23 by the disc-spring cartridge 40 may be relieved by extending (raising) a chuck-jaw actuator 50 which acts against the bottom of the actuating rod 42 to compress the disc-springs 41 and move (raise) the enlarged end portion 36 of the actuating shaft 35 out of engagement with the collet fingers 25 as shown in FIGS. 1 and 3 so that the collet fingers 25 can flex inwardly during assembly of the removable collet section 3 and workpiece W onto the fixed collet section 2 and removal therefrom. Conversely, when the chuck-jaw actuator 50 is retracted (lowered), such downward movement of the chuck-jaw actuator 50 releases the spring cartridge 40 so that the disc-springs 41 are free to act on the rod 42 causing the rod 42 and shaft 35 to move downwardly to provide the desired arbor clamping force in the manner previously described. Such downward and upward movements of the chuck-jaw actuator 50 may in turn be transmitted to the chuck jaws (not shown) to cause the chuck jaws to move radially inwardly and outwardly into and out of clamping engagement with the exterior of the workpiece W. The chuck itself may be conventional and does not form any part of the present invention. However, the clamping of the exterior of the workpiece W by the chuck jaws reacts the machining forces thus allowing the workpiece W to be both roughened out and machine finished during a single clamping operation rather than two separate clamping operations.

From the foregoing, it will now be apparent that the arbor assembly of the present invention insures concentricity between the workpiece and spindle center and also effectively applies a clamping force to the workpiece to maintain the workpiece in the desired concentric relation utilizing a collet without placing undue stresses on the collet.

Although the invention has been shown and described with respect to a certain preferred embodiment, it is obvious that equivalent alterations and modifications will occur to others skilled in the art upon the reading and understanding of the specification. The present invention includes all such equivalent alterations and modifications, and is limited only by the scope of the claims.