STEADY REST FOR ROTATING SHAFT
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.
This application claims priority of U.S. Provisional Patent Application filed Dec. 8, 2006 having Ser. No. 60/869,142.
FIELD OF THE INVENTIONThe 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 INVENTIONTurning 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
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 INVENTIONThe 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.
The description refers to the accompanying drawings in which like reference characters refer to like parts throughout the several views; and in which:
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
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
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
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
Referring to
Each plate's body section 64 includes two sides 74 and 76 that generally define its width. As best shown in
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
As shown in
Further, the present invention improves accuracy and centering of a rotating workpiece through the placement of the precision camming surfaces 20a, 20b 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 20a, 20b 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.
Type: Application
Filed: Dec 7, 2007
Publication Date: Jun 12, 2008
Inventor: Richard J. Lessway (Bloomfield Hills, MI)
Application Number: 11/952,427
International Classification: B24B 41/06 (20060101);