US3459419A - Work holding and driving devices - Google Patents

Description

5 1969 c. 0. LILLIE 3,459,419 I WORK HOLDING AND DRIVING DEVICES I Filed net. 21, 4966 2.8heets-Sheet 1 FIG-4.

Aug. 5, 1969 c. D. LILLIE WORK HOLDING AND DRIVING DEVICES 2 Sheets-Sheet 2 Filed Oct. 21, 1966 United States Patent 3,459,419 WORK HOLDING AND DRIVING DEVICES Charles D. Lillie Cornerways, Coventry Road, Bickenhill, Sollihull, England Filed Oct. 21, 1966, Ser. No. 588,594 Int. Cl. B25!) 1/24; B23q 3/05 US. Cl. 269-267 3 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION This invention relates to work holding and driving devices. There are basically two different kinds of devices which have common features and to which the invention is applicable. First there are work holding devices incorporating essentially a plurality of work contacting members such as vice jaws, plungers or the like, which are individually mounted for displacement relative to the work and to a common body or housing, these devices being used as machine vices, fixtures or jigs for example in milling machines, and which may be built into the machine or as separate and portable or transportable devices; secondly there are driving centers in which the workpiece is steadied and supported on a live or dead center usually with a conical nose to contact the work, and the center may be fixed to the body of the device or (preferably) displaceable relative thereto against resilient means, and incorporating essentially a plurality of further work-engaging jaws, plungers or the like disposed about the center and again individually mounted for displacement relative to the work and to the body or housing.

Known devices of these kinds use a common body of hydraulic fluid which acts upon all of the plurality of jaws or plungers or the like, so that application of pressure to the fluid by a displaceable piston, or from a separate fluid pressure source applies equal pressure to the jaws so that work is clamped at the plurality of points at equal pressure irrespective of variations in work-piece shape or dimensions. These known devices are perfectly satisfactory if well designed and made, but the high fluid pressures necessary, of the order of e.g. 6000 lbs. per square inch necessitate very accurate manufacture and complex seal arrangements so that the known devices are essentially precision instruments which are both expensive and susceptible of damage by semi-skilled or unskilled operators who use the devices.

SUMMARY OF THE INVENTION The object of the present invention therefore is to provide equally satisfactory devices which are of more simple design and are apt for manufacture at less cost.

In accordance with the invention a work holding or driving device comprises a body, a plurality of workengaging parts displaceable relative to the body, and a pad of solid material contained in the body and substantially filling a chamber therein, all of said parts being disposed so that in said displacement the material is contacted and deformed, and said solid material being characterise by physical properties which permit it to be moulded to the desired chamber shape thermoplastically,

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but not at normal atmospheric ambient temperatures, or being sufficiently hard at said temperatures to be cut to the desired shape.

One example of suitable material is the grade of polyurethane sold under the trademark Presollan by John Bull Rubber Co. Ltd., of Leicester, England. This polyurethane may be moulded by normal plastics technique at elevated temperatures to form the desired chamberfilling shapes, or cut from the sheet or block by punches, dies, cutting knives or the like, and in the shaped form possesses sufficient rigidity to maintain its shape and dimensions at normal temperatures to which it may be subjected prior to assembling.

In use, the material would tend to extrude under high pressures, but to only a fraction of the extent to which hydraulic oils and fluids seep through joints, and therefore it is found sufiicient to provide high quality smooth surfaces on the parts which cooperate to define the chamber and house the displacetble part without providing O-ring seals or the like to prevent loss of the material.

The design of the devices is therefore simplified. It is however necessary to keep all of the displaceable parts relatively close together; for example if a jig is made to machine large castings, e. g. in the automobile industry and the casting is to be held and clamped at its periphery by eg three equispaced plungers, the plungers could all act upon a large diameter annulus of the material, but it is preferred to couple the plungers by lever mechanisms so that the levers act directly or by secondary plungers upon a relatively small pad of material. Alternatively, instead of using levers, each plunger could act in one end of a passage or bore filled with a rod of the material and the passages could be interconnected so that pressure in all passages is identical.

BRIEF DESCRIPTION OF THE DRAWINGS FIGURE 1 is a plan view of a work holding device;

FIGURE 2 is a section taken on the line 2-2 of FIG- URE 1;

FIGURE 3 is a sectional elevation of a work driving device;

FIGURE 4 is a plan view thereof; and

FIGURE 5 is a side elevation of a part of the driving device shown in FIGURES 3 and 4.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings and particularly to FIG- URES 1 and 2 thereof, the work holding device comprises a parallelepiped body 19 formed of two parts (see FIG- URE 2) namely a bored part 10a and a cap plate 10b. The parts are held together by a series of bolts 11. The bored part 10a is provided with a row of bores or apertures each of which slightly accommodates a plunger 12. The bores are of two diameters and the plungers are similarly shaped so that a shoulder 13 on each plunger may contact a complementary shoulder 14 in the bores to prevent the plungers from being withdrawn from out of the bores when the device is assembled as shown in FIGURE 2.

Each of the bores opens at the face which is contacted by the plate 1% to a common chamber which extends along the length of the body. Hence all of the bores open to the common chamber.

The common chamber accommodates a pad of Prescollan which is of a complementary shape to the chamber and is apertured locally to permit two of the securing bolts to extend therethrough. All of the plungers seat upon the Prescollan.

Referring now to FIGURES 3 to 5 of the drawings the arrangement shown therein comprises a generally circular body 30 having a peripheral flange 31 provided with equi-spaced apertures 32 facilitate bolting to a lathe part.

The body 30 is axially bored to accommodate a centering pin 33 and concentrically of the pin axis is provided an annular recess 34 opening to the substantially planar face of the body to receive an annulu of Prescollan.

The device has a further body part 35 secured to the body 30 by a series of equi-spaced screws 36 and this body part is provided with a bore for the centering pin 33 and With a series for example of four equi-spaced parallel bores located on a pitch circle concentric with the axis of the pin 33 and each of which accommodate a drive pin 37.

The drive pin bores open to eccentrically located larger diameter bores 38 each of which accommodates a plunger 39 and the plungers extend through the end face of the body part 35 and seat upon the Prescollan annulus.

On the other end of the body part 35 the pin bores also open into enlarged diameter portions which in this case are co-axial therewith and within each such enlarged diameter portion is located a driver 40. The drivers have chisel edges 41 as best seen in FIGURES 4 and and the chisel edges lie in planes radial to and containing the axis of the centering pin 33, being held and retained in these planes by cross pins 43 extending through transverse bores in the body part 35 and through slots 44 provided for this purpose in the drivers.

At the opposite end of the body 30 the centering pin has a shoulder 50 which forms an end abutment for a spring 51 which is held under compression by seating against the shoulder 52 in the cap 53 held in place by equi-spaced pins 54.

In operation (in both cases) movement of any one of the plungers towards the pad of Prescollan causes a local deformation of the latter and this transmits pressure throughout the Prescollan body to act upon the other plungers so that the pressure acting upon all of the plungers is substantially equalised.

Thus in the case of FIGURES 1 and 2 the various plungers shown thereon may be displaced to different heights relative to the body to accommodate a workpiece of irregular contour but may maintain substantially constant pressure on the workpiece at each of the points of contact.

Similarly in the case of FIGURES 3 to 5 the centering pin is displaced against the spring 51 to take the workpiece into contact; with the chisel edges which transmit driving force to the workpiece through rotation of the latter in the machine tool in which the driver is used, the

individual drivers 40 possibly being displaced through different distances, and the displacement being transmitted by the pins 37 and the plungers 3? and hence via the pad of Prescollan 55 so that these pressures are again all equalised.

Whilst the invention has been particularly described with reference to the use of Prescollan, it is believed that any solid material with similar characteristics may be employed.

It has been found experimentally that a device as shown in FIGURES 1 and 2 is considerably cheaper and simpler to produce than an equivalent but hydraulic device, and has a longer life in service.

I claim:

1. A Work engaging device comprising a body, a plurality of separate bores provided in said body, each of said bores opening into a chamber which is common to all of said bores, a plunger slidable in each of said bores, and a pad of solid but yielding material which is of the same shape and dimensions as said chamber and is located in and fills said chamber, each of said plungers having one end seating on the pad and the other end projecting from V the body for work engagement.

2. A device a claimed in claim 1 wherein each of said bores comprises a first part opening into said chamber and a second part, of smaller cross-sectional area than first part, opening to the exterior of the body, and each of said plungers comprises two parts to fit the two parts of the bore in which the plunger is slidable, the length of the larger part of each plunger being short relative to the length of the larger part of its bore so that the plunger is freely slidable in its bore but is restrained against moving completely out of its bore.

3. A device as claimed in claim 1 wherein the solid material is a polyurethane.

References Cited UNITED STATES PATENTS 6/1929 Joksch 269267 2/ 1939 Groene 269267 X US. Cl. X.R. 269286, 310

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