US20080139092A1

US20080139092A1 - Steady rest for rotating shaft

Info

Publication number: US20080139092A1
Application number: US11/952,427
Authority: US
Inventors: Richard J. Lessway
Original assignee: Individual
Current assignee: Individual
Priority date: 2006-12-08
Filing date: 2007-12-07
Publication date: 2008-06-12

Abstract

An improved steady rest assembly having a pair of opposed gripper arms that selectively open and close around a rotating cylindrical workpiece. One end of the gripper arms includes a workpiece-engaging member while the opposite end is pivotally coupled to a stationary base portion. Each gripper arm has a precision cut camming groove located between the two ends. A linearly translating yoke carries a third workpiece-engaging member and a pair of camming pins that slidably mates with these camming grooves to open and close the gripper arms. As the yoke moves toward a workpiece, the three workpiece-engaging members close around and center the workpiece.

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority of U.S. Provisional Patent Application filed Dec. 8, 2006 having Ser. No. 60/869,142.

FIELD OF THE INVENTION

The present invention relates to steady rests employed to support a cylindrical workpiece for precision machining or grinding. More specifically, this invention relates to an economical multi-point, true centering steady rest having a pair of arms having two opposed precision cut camming surfaces which cooperate to close the arms around a workpiece.

BACKGROUND OF THE INVENTION

Turning of cylindrical objects on a lathe or similar machine tool oftentimes requires a device known as a “steady rest” to hold the free end or middle of a long workpiece while it is being machined. Conventional steady rests often include three rotating centers that cooperatively surround and grip the rotating workpiece. In most of the prior art steady rests, such as steady rest 1 illustrated in FIG. 8, two of the centers 2 are located on the ends of gripper arms 3 that open and close together due to the operation of precision ground camming surfaces 4 found on the ends 5 of the arms opposite to the rotating centers 2. The arms pivot about a centrally located pin 6. A third roller 7 translates linearly toward the workpiece while centers 2 ride on arms 3 in an arcing pattern to grip the workpiece on three sides.
If the camming surface 4 is not shaped correctly, the center 2 will not hold the workpiece properly and potentially cause the steady rest 1 to not hold a “true” or accurate centered support. Therefore, these camming surfaces must be manufactured to very high tolerances, requiring multiple expensive finishing operations, including precision grinding operations, thereby undesirably increasing the cost of the steady rest 1.
A need exists for a simplified high-precision steady rest that

SUMMARY OF THE INVENTION

The broad purpose of the present invention is to provide an economical steady rest that overcomes the high costs of conventional steady rests. In the preferred embodiment of the invention, a steady rest is provided having two opposed gripper arms. Each arm includes a workpiece-holding roller or wear pad on one end and is pivotally coupled at its opposite end to the steady rest's body. Each arm also includes a camming groove formed between the pivot end and the roller end. A yoke carrying a third roller/wear pad and two sets of camming pins coupled to the arms. Each set of camming pins is contained within the camming groove.
This improved steady rest further includes a linear actuator which causes the yoke to move, thereby causing the gripper arms to open and close relative to the workpiece. In the preferred embodiment, the camming grooves are formed in the gripper arms in a single precision machining operation, such as laser cutting, to reduce the production cost of the steady rest.
Still further objects and advantages of the invention will become readily apparent to those skilled in the art to which the invention pertains upon reference to the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The description refers to the accompanying drawings in which like reference characters refer to like parts throughout the several views; and in which:

FIG. 1 is a perspective view of the steady rest assembly;

FIG. 2 is a front view of the steady rest having one of its base plate removed for clarity;

FIG. 3 is a perspective view of one of the push plate halves;

FIG. 4 is partially assembled front view of the yoke, push plate, and one of the base plates;

FIG. 5 is a perspective view of one of the base plates;

FIG. 6 is an exploded perspective view of a pivot pin and arm spacer;

FIG. 7 is a front view of one of the arm plates;

FIG. 8 is a perspective view of a camming pin; and

FIG. 9 is a perspective view of a prior art steady rest with one of its side cover plates removed.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the Figures, a steady rest 10 is illustrated having a pair of opposed gripping arms 12 that are pivotally coupled to a stationary base or body portion 14. A sliding yoke 16 carries a pair of camming pins 18 that are mounted in camming grooves 20 formed in the arms 12.
Steady rest 10 also includes a linear actuator 21, such as a hand wheel and screw assembly, having a threaded rod 22 which turns with the hand wheel. The threaded rod 22 is threadably received by a push pin 24 that runs orthogonal to the piston rod. The actuator's threaded rod 22 and push pin 24 are arranged such that push pin 24 rides along rod 22 as it is rotated. Push pin 24 moves linearly along an axis 25 toward and away from the centerline of an elongated workpiece 23 (illustrated in phantom). The workpiece may be a shaft or other generally cylindrical object undergoing a metal finishing or turning operation. In other embodiments, linear actuator 21 may be a hydraulic or pneumatic power cylinder.
Referring now to FIGS. 2-4, yoke 16 includes a push plate 26. In the preferred embodiment, push plate 26 is formed from two identical generally rectangular plates 27. As shown in FIG. 3, each plate 27 includes a semi-circular channel 28 formed in its rearward end (i.e., adjacent to actuator 21). Channel 28 is sized such that when the two plates 27 are mated together, a blind hole is formed that is sized to rotatably receive threaded rod 22. An enlarged recess 28 a, is formed within each plate 27 proximate to the rearward end. Recess 28 a is sized to fixedly retain push pin 24. A bore 29 is formed proximate to the forward end (adjacent the workpiece) of plate 27 and is sized to receive a complementary portion of a workpiece-engaging member or roller 30. That is, the two bores 29 formed in the forward ends of the push plate 26 cooperate to form a clevis. This clevis operates to rotatably retain the workpiece-engaging roller 30. In one embodiment, member 30 is a conventional roller and includes an axle pin 31 and a round work-engaging bearing surface 32.
Each plate 27 also includes a groove or channel 33 that is sized to retain the center portion 34 of a yoke body 35. Push plate 26 is aligned with axis 25 such that its channels 33 are perpendicular to axis 25, the longitudinal axis of channel 28 is axially aligned with axis 25, and the centerline of bore 29 passes perpendicularly through axis 25.
As best shown in FIGS. 2 and 4, yoke body 35 is a rigid block-like member having a rectangular center portion 34. Shoulders 36 extend from the opposite ends of portion 34. Both shoulders 36 angle from portion 34 in the same general direction as roller 30. A camming pin bore 38 is formed through each shoulder 36. Bores 38 are located within yoke body 35 such that the centerlines of bores 38 and the center line of roller 30 are both parallel and co-planar to each other. When assembled, the two plates 27 sandwich the yoke body 35 within channels 33 and the yoke body 35 and push plate 26 are fastened together.
The linear actuator 21 is coupled to yoke 16 at the rearward end (i.e., the end opposite to yoke body 35) of push plate 26.
Referring now to FIGS. 1 and 5, the base 14 includes a pair of parallel, generally flat base plates 40. To simplify production and reduce cost, the two base plates 40 are identical. The inner face 41 of base plate 40 includes a generally rectangular center channel 42 that traverses the entire plate. Channel 42 has a width that is sized to receive the width of the push plate 26. Base 14 is formed by sandwiching the base plates 40 around push plate 26. Push plate 26 is slidably engaged within the two channels 42.
Four bores 46 are formed through the plates 40. Additionally, two pivot pin bores 48, 50 are also formed in the inner face 41 adjacent to opposite ends of the plates. A coaxial smaller diameter through bore 51 passes continues through the plate. It should be appreciated that bores 46, 48, 50, and 51 are all formed perpendicular to the prevailing flat faces (e.g., face 41) of the base plate 40.
Four body spacers 52 are provided and are sized to fit within bores 46 formed through the plates 40. Body spacers 52 cooperate to maintain a fixed spacing between the base plates. In the preferred embodiment, a through hole 53 is formed along the centerline of each spacer 52. These through holes 53 enable a user to pass fasteners through the steady rest 10 to couple the steady rest to a support or a portion of a machine tool (e.g., a lathe).
Referring to FIGS. 1, 2, and 4-6, two identical pivot pins 54 are provided and are fixed within bores 48, 50. Pins 54, like body spacers 52 and push plate 26, are sandwiched between plates 40 when base 14 is assembled. Each pin 54 has two ends 56, 58 having a diameter that is complementary to the bores 48, 50. The center portion 60 has a larger diameter than the ends 56, 58 forming two shoulders that abut the inner faces 41 of the base plates 40 when base 14 is assembled. Each end 56, 58 is tapped along the centerline of the pin to receive a threaded fastener 61. These threaded fasteners 61 pass through coaxial holes 51 and into pivot pins 54 to couple the base 14 together. In the preferred embodiment, only fasteners 61 and pivot pins 54 operate to hold the base 14 together, thereby making disassembly of steady rest 10 faster and easier.
Referring to FIGS. 1, 2, 6, and 7, gripping arms 12 are formed from two identical and parallel arm plates 62 that sandwich yoke 16. Each plate 62 is generally flat and contiguous and includes a body section 64 and two outwardly projecting flanges 66 and 68. Flanges 66 and 68 angle away from opposing sides of body 64 and represent the two “ends” of arm plate 62. Flange 66 includes a through bore 70 formed proximate to its outer edge. Bore 70 is sized complementary to the diameter of pivot pin center portion 60. Similarly, flange 68 includes a through bore 72 proximate to its edge. Bore 72 is sized to receive the axle pin of a conventional workpiece-engaging member or roller 73. In the preferred embodiment, roller 73 is identical to roller 30. In other embodiment, rollers 73 and roller 30 are replaced with wear pads.
Each plate's body section 64 includes two sides 74 and 76 that generally define its width. As best shown in FIG. 1, each camming slot 19 is cooperatively formed and includes a pair of aligned cam slots 20 formed in each arm plate 62. Each cam slot 20 is defined by a pair of opposed camming walls or surfaces 20 a and 20 b formed within body section 64 between sides 74, 76. As will be described in greater detail below, camming slot 19 (and each individual cam slot 20) has an arcuate shape that is suited for opening and closing arms 12. The arcuate shape is concave relative to outermost side 76 of arm plate 62. In the preferred embodiment, each cam slot 20 is precision cut from the body section 64 in a single operation. A precision cutting operation, such as laser cutting, is preferably used to eliminate the need to perform a secondary operation to finish the camming surfaces 20 a and 20 b, thereby reducing production time and cost.
When a gripper arm 12 is assembled, a pivot pin bore 70 of a first arm plate 62 is slid over the center portion 60 of a pivot pin 54. A tubular arm spacer 80 is then placed over the center portion 60. Next, the pivot bore 70 of a second arm plate is fitted over portion 60 of the pivot pin. In this manner, the two parallel arm plates 62 are pivotally connected to a pivot pin 54 and sandwich one end of yoke 16, leaving the plates 62 in a spaced parallel arrangement. This spaced arrangement causes the roller bores 72 in flange 68 to form a clevis that receives and retains workpiece-engaging roller 73 in a manner that is substantially the same as the clevis formed in the forward end of push plate 26.
Steady rest 10 is assembled by sandwiching the two base plates 40 around the push plate of yoke 16 (retained within the two facing channels 32).
It should be appreciated that the length of center portion 60 of the pivot pins 54 and the portion of body spacers 52 that is sandwiched between inner faces 41 are both slightly larger than the combined thicknesses of two arm plates 62 and the length of arm spacer 80, thereby allowing clearance to pivot the arm 12 within the body portion 14.
Referring now to FIGS. 1, 2, and 8, steady rest 10 includes two camming pins 18. Camming pin 18 includes a cylindrical shaft 82. Shaft 82 has a diameter that forms a slip-fit arrangement with yoke bores 38. Two concentric grooves 84 are formed on the outer surface of shaft 82. Each of the grooves 84 being proximate to the opposite ends of the shaft. Two roller bearings 86 and 88 are fitted onto shaft 82, between grooves 84. Bearings 86 and 88 are separated a distance slightly larger than the thickness of yoke 16. Roller bearings 86 and 88 are sized to slidably fit within the opposed cam slots 20, i.e., between the opposed camming surfaces 20 a, 20 b. A washer 90 covers the roller bearing 86 and is held in place by a conventional fastener, such as a snap ring 92 that is retained within groove 84.
As shown in FIG. 2, the gripping arms 12 are movable from an open position illustrated at A to a fully closed (i.e., a minimum workpiece diameter) position illustrated at B. Forward movement (upward in FIG. 2) of the push plate 26 results in both the forward mounted roller 30 and the two camming pins 18 to move linearly toward workpiece 23. The shape of camming slots 19 are such that the linear movement of camming pins 18 causes the rollers 73 in gripping arms 12 to close in toward workpiece 23 at the same rate and distance as roller 30. In this manner, steady rest 10 provides an economical three-point, true centering support for a rotating workpiece.
Further, the present invention improves accuracy and centering of a rotating workpiece through the placement of the precision camming surfaces 20 a, 20 b of cam slots 20 between the gripper arm's pivot point (pivot pin 54) and the work-engaging member 73. This central location of the camming surfaces 20 a, 20 b reduces any deflection or misalignment at the work-engaging members 73 caused by any imperfections, debris or any other impediments found within camming pins 18 or the camming surfaces.
From the foregoing description, one skilled in the art will readily recognize that the present invention is directed to a steady rest that provides high accuracy and repeatability, while remaining uncomplicated and inexpensive by the novel application of shaped gripper arms having precision cut camming slots formed therein
While the present invention has been described with particular reference to various preferred embodiments, one skilled in the art will recognize from the foregoing discussion and accompanying drawings that changes, modifications, and variations can be made in the present invention without departing from the spirit and scope thereof.
The invention has been described in an illustrative manner, and it is to be understood that the terminology, which has been used, is intended to be in the nature of words of description rather than of limitation.

Claims

1. A steady rest for gripping a rotating workpiece, comprising:

a non-moving base; and

a gripping assembly comprising:

a pair of opposed gripper arms that selectively open and close around said workpiece, one end of the gripper arms includes a workpiece-engaging member while the opposite end is pivotally coupled to said base, wherein each gripper arm includes a pair of opposed precision cut camming walls, which define a camming slot, located between the two ends; and

a yoke which is slidably mounted upon said base and which carries a third workpiece-engaging member and a pair of camming pins, each camming pin is slidably mated within one of said camming slots to open and close said gripper arms;

wherein said gripping assembly is movable between an open position where the three workpiece-engaging members are remote from the workpiece and a closed position where the three work-engaging members abut and center the workpiece.

2. A steady rest as defined in claim 1, wherein each of said gripping arms comprise:

a pair of parallel arm plates which are separated by and sandwich said yoke, each of said arm plates including a cam slot;

wherein said camming pin slidably mates with and aligns both of said cam slots, which cooperatively define one of said camming slots.

3. A steady rest as defined in claim 2, wherein said camming pins include two roller bearings, wherein each of said roller bearings is received within and abuts one of said arm plate cam slots.

4. A steady rest as defined in claim 1, wherein said yoke comprises:

a push plate; and

a body having two shoulders at opposite ends of said body, said body is mounted to said push plate whereby said shoulders project away from said push plate.

5. A steady rest as defined in claim 1, further comprising:

actuator means coupled to said yoke and which cause said yoke to translate linearly relative to said base.

6. A steady rest as defined in claim 1, in which said workpiece-engaging members each comprise a roller.

7. A steady rest as defined in claim 1, wherein each of said gripping arms have an inner side wall and an outer side wall, and wherein each of said camming slots is concave-shaped relative to said outer side wall.

8. In a workpiece gripping apparatus, a combination comprising:

a stationary housing;

a yoke having a center workpiece-engaging member extending from one end of said yoke and a pair of outwardly projecting shoulders, said first workpiece-engaging member is flanked on two sides by said shoulders, wherein said workpiece-engaging member is mounted within a center bore having a centerline and each shoulder includes a camming pin bore having a camming pin centerline which runs parallel to and co-planar with said center bore centerline;

a pair of camming pins having two concentrically mounted roller bearings, each camming pin is mounted within and extends from one of said camming pin bores whereby each roller bore is located on opposite sides of said shoulder; and

a pair of elongated gripping arms, said gripping arms terminating at one end at an outer work-engaging member, each gripping arm includes a pivot point at the end opposite to the outer work-engaging member, each gripping arm comprising:

a pair of identical parallel spaced arm plates, each arm plate including a pair of opposed arcuate camming walls, which define a cam slot located between the pivot point and the end terminating at the outer work-engaging member;

said spaced arm plates sandwich said shoulders and said roller bearings abuttingly engage said camming walls in one of said spaced arm plates; and

a pivot pin mounted to said pivot point and to said body;

wherein said yoke is linearly moveable within said housing, effective to cause said roller bearing to engage said camming walls and rotate said gripping arms about said pivot pins.

9. A combination as defined in claim 8, wherein said yoke further comprises a push plate which extends away from center work-engaging member.

10. A combination as defined in claim 9, further comprising actuator means coupled to said push plate and which cause said yoke to translate linearly relative to said housing.

11. A combination as defined in claim 8, in which said workpiece-engaging members each comprise a roller.

12. A combination as defined in claim 8, wherein each of said arm plates have an inner side wall and an outer side wall, and wherein each of said cam slots is concave-shaped relative to said outer side wall.

13. A method of forming an economical steady rest for holding a rotating workpiece, comprising the steps of:

forming an arcuate precision cam slot into an elongated arm plate between a pivot bore and a work-engaging end in only a single cutting process;

providing a yoke having a work-engaging member at one end and a pair of shoulders flanking said work-engaging member;

sandwiching a pair of said arm plates around each of said shoulders to form a pair of gripping arms;

mounting a pivot pin through said shoulder and said cam slots of each gripping arm;

pivotally mounting said gripping arms to a base at said pivot bores; and

slidably mounting said yoke to said base, whereby said gripping arms rotate about said pivot bore and follow said cam slot as said yoke is translated along said base.

14. A method as defined in claim 13, wherein said single cutting process is a laser cutting process.

15. A method as defined in claim 13, further comprising the steps of:

mounting a linear actuator to base; and

coupling said linear actuator to said yoke, effective to cause said yoke to translate linearly along said base.