US3812629A

US3812629A - Workholder

Info

Publication number: US3812629A
Application number: US00280899A
Authority: US
Inventors: P Campbell
Original assignee: Individual
Current assignee: Individual
Priority date: 1972-08-15
Filing date: 1972-08-15
Publication date: 1974-05-28
Anticipated expiration: 1991-05-28

Abstract

A workholder of the magnetic type having movable magnetic elements to render it selectively either operative or inoperative.

Description

[ May 28, 1974 United States Patent [1 Campbell 2,635,495 4/l953 Thompson 269/80 3,452,310 6/1969 lsraelson......,.................. 335/295 X FOREIGN PATENTS OR APPLICATIONS 563,333 Great Britain...................... 335/295 243,383 5/1969 269/8 [22] Filed:

Primary Examiner-Harold D. Whitehead or FirmNorman S. Blodgett; Gerry S k .w m B A S R a w a B m A r e t mn w X t E t nWd mmw WW n 5 AAA 50 6 m w 2 2 2/12/ M51 3 75 3 8; ZQMW 00 B5 w .3/ 6 M 5 R 6 m l .W n "6 1 m m mh .r u "a n n L h C in S WM U mm 11 .l] 2 l8 5 55 A workholder 0f the magnetic type having movable magnetic elements to render it selectively either operative or in-operative.

References Cited UNITED STATES PATENTS 1,828,791 Thompson 269/8 10 Claims, 17 Drawing Figures PATENTEDm 28 1914 FIG.

FIG. 3

FATENTEDMM 2 8 ISM sumznra FIG. 4

FIG. 6

PAIENIEUIAY 28 I974 SHEET 3 OF 4 IION II J POSITION [3 "II FIG. ll

FRONT FIG. I0

24 24 I3" 23 2 W Q BACK FIG. I3

POSITION FRONT FIG. I2

BACKGROUND OF THE INVENTION In the machining of workpieces it often is necessary, not only to hold the workpiece in a firm fixed position, but also to locate it accurately relative to the machine tool spindle. The simplest way of accomplishing this is by the use of a clamping means, such as a vice. For workholders of this type have inherent drawbacks, in that they intend to warp the workpiece so that when the workpiece is removed the finished surface is no longer accurate and they also have a tendency to mar the surface of the workpiece. Magnetic workholders, therefore, have been developed which hold the workpiece without marring its surface, and in such a way as not to develop stress in the workpiece during machining. Magnetic workholders, however, have their own drawbacks, not the least of which is the fact that, they are not readily adapted to work with a wide range of types and sizes of workpieces. As a matter offact, they are usually customed manufactured for use with a particular workpiece and cannot be used with other workpieces. It then becomes necessary, in order to machine a variety of work, to have available a large number of expensive magnetic workholders. These and other difficulties experienced with the prior art devices have been obviated in a novel manner by the present invention.

It is, therefore, an outstanding object of the invention to provide the workholder capable of firmly holding a workpiece without marring its surface.

Another object of the invention is the provision of a workholder adapted to hold a variety of workpieces.

A further object of the present invention is the provision of a magnetic workholder which is simple in construction and yet which is capable of holding workpieces having a wide range of shape and size.

It is another object of the instant invention to provide a magnetic workholder in which the magnetic lines of force are concentrated in the workpiece being held in such a manner as to give large holding forces for a given size of magnet.

A still further object of the invention is the provision of a magnetic workholder which is simple in construction, inexpensive to manufacture, and which is capable of a long life of useful service with a minimum of maintenance.

It is a further object of the invention to provide a magnetic workholder having a configuration which concentrates the magnetic lines of force tomake a very effective use of the magnetic forces available.

SUMMARY OF THE INVENTION In general, the invention consists of a workholder having a base adapted to be mounted on a flat surface, having a-platen pivotally mounted on the base and having a primary magnetic element. Means is provided for locking the platen in a predetermined angular relation ship to the base. A movable secondary magnetic element is provided for rendering the primary magnetic element on the platen selectively operative or nonoperative I I More specifically, the secondary magnetic element is rotatably mounted in the platen for rotation about the same pivotal axis as the platen is mounted on the base.

BRIEF DESCRIPTION OF THE DRAWINGS The character of the invention, however, may be best understood by reference to one of its structural forms,

as illustrated by the accompanying drawings, in which:

FIG. 1 is a prospective view of a workholder embodying the principles of the present invention,

FIG. 2 is a side elevational view of the workholder,

FIG. 3 is an end elevational view of the workholder,-

FIG. 4 is a side view of the workholder showing a method of squaring it with a reference surface,

FIG. 5 is a side view of the workholder, showing a method of setting it at a predetermined angle to a reference surface,

FIG. 6 is a view of the workholder showing how it can be used to hold a thin workpiece in an upright position. For instance, for grinding one edge,

FIG. 7 is a prospective view of the workholder showing how. it can be. used to hold a elongated thin workpiece for grinding or the like, i

FIG. 8 is an end view of the workholder showing a still further way in which it can be used to hold unusually shaped workpieces,

FIG. 9 is an exploded view of the parts of a platen forming a major part of the workholder,

FIGS. l0l3 are schematic views showing various conditions in the workholder,

FIG. 14 is a sectional view through the center of the platen in its on position,

FIG. 15 is a sectional view through the end of the platen in its on position,

FIG. 16 is a sectional view through the center of the platen in its off position, and

FIG. 17 is a sectional view through the end of the platen in its off position.

Referring first to FIG. 1 wherein are best shown the general features of the invention, the workholder indicated generally by the reference numeral 10, is shown as having a base 11 which is adapted to be mounted on a flat horizontal surface such as the surface of the table of a machine tool, the platen 12 is pivotally mounted on the base and is provided with a primary magnetic element 13, a means such as a clamp 14 is provided for locking the platen 12 in a selected angular position relative to the base 11. A movable secondary magnetic element 15 is provided for rendering the first magnetic element 13 selectively operative or non-operative. The secondary magnetic element is mounted in the platen 12 for rotation about the same axis as the platen is mounted for angular adjustment relative to the base 11, but the rotation of the magnetic element 15 is independent of the rotation of the platen relative to the base.

having opposite flatsides l8 and 19. The pivotal axis of the platen relative to the base passes through the points of intersection of an imaginary diagonal line joining the corners of the platen.

Referring now to FIG. 9, it can be seen that a primary magnetic element 13 is imbedded in each comer of the platen, there being four such magnetic elements indicated by the

numerals

13, 13", 13 and 13"". Each of these four magnetic elements are arranged with its north-to-south axis perpendicular to the flat side of the platen. The elements at the end of one edge of the platen having this axis in the north-to-south mode, while the elements at the ends of the edge of the platen have this axis in the south-to-north mode. The platen is provided with a bore 21 which is concentric to the pivotal axis of the platen relative to the base l1.'The secondary magnetic element or plug is shown as a cylindrical plug which fits snugly but rotatively in this bore. The plug is provided on one side with magnetic elements 22 and on the diametrically opposite side with magnetic elements 23. These magnetic elements are arranged with their north-south axises perpindecular to the flat sides of the plug. That is to say, parallel to the axis. The magnetic elements 22 on one side are arranged in the north-to-south mode, while the magnetic elements 23 on the other side are arranged in the southto-north mode.

FIG. 9 shows particularly well that the platen 12 is formed in three parts with a central plate 24 sandwiched between

side plates

25 and 26. The central plate 24 is the one which carries the primary magnetic elements 13 and is provided with the central bore 21 in which rests the secondary magnetic element 15. The side plate 25 consists of two spaced

parallel strips

27 and 28 formed of steel and joined by a central strip 29 formed of non-magnetic material. Similarly, the other side plate 26 is formed with two spaced

parallel steel plates

31 and 32 between which runs a strip 33 of nonmagnetic material, such as copper.

The edges of the platen 12 are provided with various configurations to assist on holding various shapes of workpieces. For instance, a one end edge of the side plate 25, is provided with a flange 34 and spaced from it on the same edge is another similar flange 35. Similarly, the corresponding end edge of the plate 26 is provided with two spaced

flanges

36 and 37. The flange 34 is typical of the four flanges and is provided with an outer edge surface edge 38 which lies outwardly of the end surface of the central plate 24, so that a workpiece held against this surface is held separated from the central plate. The flange 34 is also provided with an inwardly directed bevel or inclined surface 39 which assists in holding cylindrical objects which are to be machined. The use of the bevel surface 39 causes the flat outer surface 38 to be relatively narrow in the transverse direction which has the effect of concentrating the magnetic lines of force. The

other flanges

35, 36, and 37 and similarly provided with outwardly directed flat surfaces similar to the flat surface 38 in the flange 34 and with inwardly directed beveled surfaces similar to the beveled surface'39 of the flange 34. There are, therefore. four beveled surfaces facing inwardly for particular usein holding cylindrical surfaces in four spaced flat surfaces for holding thin workpieces.

The operation of the invention will now be readily understood in view of the above description. The face 11 is mounted on a flat horizontal surface, such as the table surface of a machine tool. Since the platen 12 is generally rectangular, and has four sides, once the side has been selected to which the workpiece is to be attached its angularity to the horizontal can be adjusted by loosening a socket screw joining the two halves of the clamp 14. The clamp, of course, operates on a pivot shaft extending laterally from both sides of the platen l2 and when the angle has been set the clamp 14 is retightened to lock the platen in place. Primary magnetic elements embeded in the platen 12 are rendered inoperative and after the workpiece has been layed along the surface of the platen 12 which has been selected, the magnetic elements are re-activated. The reactivation and the activation of the magnetic elements takes place by rotating the external shaft of the secondary magnetic element 15 by means of an Allen wrench. FIGS. 10 through 13 show the various conditions of the magnetic elements. FIGS. 10 and 11 show the magnetic elements in actuated condition and FIGS. 12 and 13 show them in in-activated condition. As is evident in FIGS. 10 and 11 the poles of the secondary magnetic elements Hand 23 are orientated with the corresponding poles of the primary magnetic elements 13. For instance, the north poles of the secondary magnetic element 22 are on the same side as the north poles of the primary magnetic elements 13' and 13", while the south poles of the secondary magnetic element 23 is on that same side along with the south poles of the primary magnetic elements 13" and 13 This is shown in FIG. 10. In FIG. 11 correspondingly it can be seen that the south pole of the element 22 is on the other side of the platen 24 along with the south pole of the elements 13' and 13'', while the north pole of the element 23 is on the other side of the platen along with the south pole of the elements 13" and 13"". In this way, the secondary magnetic element reinforce and add to the magnetic lines of force produced by the primary magnetic elements.

In order to render the holding power of the platen substantially zero, it is only necessary to rotate the plug 15, as is evident in FIGS. 12 and 13. When the plug 15 has been rotated the poles of the

secondary elements

22 and 23 are opposite those of their adjacent primary magnetic elements. For instance, in FIG. 12 it can be seen that the south pole of the element 23 extends from the same side of the platen 24 as the north pole ofthe elements 13' and 13". The north pole of the element 22 extends from the same side of the plate as the south poles of the elements 13" and 13. Of course, on the other side of the plate 24, as is evident in FIG. 13, it can be seen that the north pole'of the element 23 extends from the same side as the south poles ofthe elements 13' and 13", while the south pole of the element 22 extends outwardly of the same side of the plate as the north poles ofthe elements 13" and 13"".,

It should be pointed out that the apparatus is always returned to the condition shown in FIGS. 12 and 13 to remove a workpiece and perhaps to replace-it with another. It is arranged to the condition of FIGS. 10 and 11 only when the workpiece is to be held tightly for machining, etc. As a matter of practical design, the areas of the various magnets are selected so that in .the OFF condition there is a slight polarity reversal to assist in the removal of the workpiece.

Diagrams of FIGS. 14 through 17 show the manner in which the rotation through 180 effects the magnetic lines of force in the platen 12. FIG. 14 shows the center of the platen when the magnetic is in the ON position. The magnetic lines of force originating in the magnetic element 22 form a loop through the

strips

27 and 31 of the two side plates and through the workpiece W. At the opposite ends of the platen the magnetic element 13 produces a magnetic loop of the same polarity as shown in FIG. 15. The loops of lines of force from the center and the ends overlap and combine to provide a reinforce magnetic attraction throughout the entire length of the platen on the workpiece W. Similar loops of opposite polarity take place at the other side of the platen and at the end edges.

This is shown in FIGS. 16 and 17 that when the center plug 15 is turned 180 the loops at the ends of the platen remain the same (as shown in FIG. 17), but those in the center are of reversed polarity which means that the lines of force cancel one another out and result in a practically negligible attraction of the workpiece W to the platen. The magnetic forces that are available during the ON condition of the platen are so strong that, if there were not means provided for deactivating them, it would be difficult, if not impossible, to place and remove a workpiece from the workholder. Furthermore, it would be difficult to adjust the workpiece once it was held on the workholder. As a matter of fact, as mentioned above, the reversal of polarity results in a slight over-reversal to assist in the removal of the workpiece.

FIGS. 4 through 8 show various aspects of the use of the invention. FIG. 1 shows the way in which the workholder can be squared up by using an accurately formed square S. The workholder is placed on a flat surface, such as a master plate, the platen clamp 14 is loosened so the platen is free to turn about its pivot. The square S is laid against one face of the platen l2 and once the platen has been made square in this manner the clamp is re-tightened. When this is done on the table of a machine tool this assures that the edges of the platen 12 are squared up with the surface of the worktable and with the axis of the spindle. FIG. 5 shows how an angle A may be used to set the platen in the same FIG. 8 shows how a workpiece W can be held on edge for grinding one thin edge by use of an L shaped support element. FIG. 6 shows the way in which the workholder 10 can be used to support a thin workpiece W. FIG. 7 shows how small pieces of metal can be used in combination to support a very small, long, thin workpiece W.

lt is obvious that minor changes may be made in the form and construction of the invention without departing from the material spirit thereof. It is not, however, desired to confine the invention to the exact form herein shown and described, but it is desired to include all such as properly come within the scope claimed.

What I claim is:

l. A workholder, comprising a a base adapted to be mounted on a flat surface,

b a platen pivotally mounted on the base and having a primary magnetic element,

0 means for locking the platen in a predetermined angular relationship to the base, and

d a movable secondary magnetic element for rendering the primary magnetic element on the platen selectively operative or in-operative, the secondary magnet being rotatable about a pivotal axis which is parallel to the north to south axis.

2. A workholder as recited in claim 1, wherein the secondary magnetic element is rotatably mounted in the platen for rotation about the same pivotal axis as the platen is mounted on the base.

3. A workholder as recited in claim 2, wherein the base is provided with two spaced parallel abutments, and wherein the platen is pivotally mounted between the abutments.

4. A workholder as recited in claim 3, wherein the platen is in the general form of a rectangular plate having opposite parallel flat sides that engage the abutments, and wherein the pivotal axis passes through a point on the platen at which imaginary diagonal lines intersect.

5. A workholder as recited in claim 4, wherein a primary magnetic element is embedded in the platen adjacent each corner, each magnetic element being arranged with its NORTH-TO-SOUTH axis perpendicular to the said flat sides of the platen, the elements at the ends of the edge of the platen having this axis in the NORTH-TO-SOUTH mode, while the elements at the ends of the opposite edge of the platen having this axis in the SOUTH-TO-NORTH mode.

6. A workholder as recited in claim 5, wherein the platen is provided with a bore concentric to the said pivotal axis, wherein the secondary magnetic element is a cylindrical plug which fits snugly in the bore, and wherein the plug is provided on diametrically opposite portions with magnetic elements arranged with their NORTH-TO-SOUTH axis perpendicular to the flat sides of the platen, one magnetic element having this axis in the NORTH-TO-SOUTH mode, while the other is in the SOUTH-TO-NORTH mode.

7. A workholder as recited in claim 6, wherein the platen consists of two side plates with a central plate sandwiched between them, wherein each side plate consists of two side-by-side strips separated by a strip of non-magnetic material, and wherein one of the strips contains both primary magnetic elements in the NORTH-TO-SOUTH mode, while the other contains both primary magnetic element in the SOUTH-TO- NORTH mode.

8. A workholder as recited in claim 7, wherein each side plate is provided along its edges with a flange having at least one surface lying outwardly of the corresponding edge of the central plate, so that a workpiece engaging the flanges is held in separation from the edge of the central plate.

9. A workholder as recited in claim 8, wherein the said flanges are beveled to provide facing inclined flat surfaces that will engage a cylindrical workpiece and also provide a narrow contact surface at the edge of the flange for magnetic flux concentration when used with a flat workpiece surface.

10. A workholder comprising a a platen having two sides and having a primary magnetic element,

b a movable secondary magnetic element for rendering the primary element on the platen selectively operative, or inoperative,

the primary magnetic element having a permanent magnet associated with each of the said two sides of the platen and the secondary magnetic element having a permanent magnet also associated with each of the said two sides of the platen,

so that there is a first magnetic circuit associated with one of the sides and a second magnetic circuit associated with the other of the sides, the rotation of the secondary magnetic element resulting in moving the said magnets to association with the other side and a neutralization of the magnetic circuit associated with that other side, the rotation taken place about a pivotal axis which is a parallel to the NORTH-TO-SOUTH axis of the secondary magnetic element.

Claims

1. A workholder, comprising a a base adapted to be mounted on a flat surface, b a platen pivotally mounted on the base and having a primary magnetic element, c means for locking the platen in a predetermined angular relationship to the base, and d a movable secondary magnetic element for rendering the primary magnetic element on the platen selectively operative or inoperative, the secondary magnet being rotatable about a pivotal axis which is parallel to the north to south axis.

7. A workholder as recited in claim 6, wherein the platen consists of two side plates with a central plate sandwiched between them, wherein each side plate consists of two side-by-side strips separated by a strip of non-magnetic material, and wherein one of the strips contains both primary magnetic elements in the NORTH-TO-SOUTH mode, while the other contains both primary magnetic element in the SOUTH-TO-NORTH mode.

10. A worKholder comprising a a platen having two sides and having a primary magnetic element, b a movable secondary magnetic element for rendering the primary element on the platen selectively operative, or inoperative, the primary magnetic element having a permanent magnet associated with each of the said two sides of the platen and the secondary magnetic element having a permanent magnet also associated with each of the said two sides of the platen, so that there is a first magnetic circuit associated with one of the sides and a second magnetic circuit associated with the other of the sides, the rotation of the secondary magnetic element resulting in moving the said magnets to association with the other side and a neutralization of the magnetic circuit associated with that other side, the rotation taken place about a pivotal axis which is a parallel to the NORTH-TO-SOUTH axis of the secondary magnetic element.