US 2471067 A
Description (OCR text may contain errors)
y 2 1949. s. 1. HITCHCOCK 2,471,067
MAGNETIC WORK HOLDER Filed Oct. 19, 1945 2 Sheets-Sheet l izyi. 2
My WQ/if W 10 14 L 51 r::: i.-. A -17 .1 4 13 25"" 13 11 u I n 5 l 11 I Q 10 "-0 PM :IU' 50 INVENTOR ATTORNEY May 24, 1949. 's. l. HITCHCOCK MAGNETIC WORK HOLDER 2 Sheets-Sheet 2 Filed Oct. .19, 1945 INVENTOR YZ'ANLEY ISAZAHH TCHCOQK BY% .a M.
ATTORNEY Patented May 24, 1949 MAGNETIC WORK HOLDER Stanley Isaiah Hitchco London, England, as-
signor to Tropical Plantations Limited, London,
England Application October 19, 1945, Serial No. 623,219 In Great Britain November 6, 1944 7 Claims. 1
Although applicable to magnetic workholders generally utilising permanent magnets for the retention of the work in position, and consequently including rotary magnetic chucks, the invention is particularly concerned with a magnetic workholder of the kind which is intended to maintain a workpiece or series of workpieces in .a stationary position during a grinding or other operation, the holder being intended either to be placed on a bench or other supporting surface, in .a vice, or even held in the hand Whilst the machining or other operation is being performed on the workpiece or workpieces.
,It has previously been proposed in the construc: ticn of such magnetic workholders to arrange the permanent magnet or magnets so that it or they are capable of controlled movement to cause the lines of magnetic flux to be diverted from their normal course in which they pass through the workpiece, and thus retain the latter in position on the face of the holding device, into a position in which the lines of magnetic flux wholly or mainly pass along .an alternative path which does not include the workpiece, and consequently permit of the removal of the latter from the Workpiece-supporting face. It will be appreciated, therefore, that the magnet or magnets is or are capable of being moved into either of two alternative positions, thus rendering the workholding device operative or inoperative at will.
In :such workholclers as previously proposed it has been the practice to arrange the pole faces of the permanent magnet or magnets in contact with the workpiece-supporting face plate, or with armature members associated therewith, and consequently it was not only necessary to grind the rubbing faces of the magnets and their cooperating ,parts accurately to ensure the parts being relatively movable, but the fact that the parts were actually in rubbing contact necessarily increased the effort required to produce relative rotational or slidin movement between the parts when it Was desired to bring the workholder into or out of operation.
The chief object of the present invention is to evolve a workholder of a more simple construction than hitherto, involving the minimum number of component parts; and which, furthermore, can be operated with the minimum of effort and in a simple manner.
The magnetic workholder according to the present invention comprises a worlosupporting surface incorporating soft iron or similar members, a permanent magnet mounted for angular movement about an axis situated at right-angles to its magnetic axis and capable of angular movement into either of two alternative positions in which the work will be held magnetically in position on the work-supporting surface and released therefrom, and fixed armature members located on opposite sides of said magnet and in spaced relationship to the magnets pole faces, said armature members being in contact with or in close proximity to the worlbsupporting surface and when the magnet is in its operative workholding position servin to connect the north and south pole magnetically to the work-supporting surface and work so that the lines of magnetic force pass freely through the soft iron members of the worksupporting surface and work, and when the magnet is in its alternative inoperative position together bridge north and south poles to provide alternative paths for the lines of magnetic flux of lower reluctance so that all or the majority of the lines of magnetic flux will no longer pass through. the Work and workholding surface and thus permit of the workpieces removal.
It will be appreciated therefore that, due to the fact that the pole faces of the permanent magnet do not actually contact the armature members but merely lie in close pr Ximity thereto, the permanent magnet capable of being moved angularly into either alternative position With the minimum of c-fiort on the part of the operator, the permanent magnet being preferably of partcylindrical formation, and consequently being balanced to rotate or partially rotate about its axis. In its operative position in which the magnetic axis passing through the north and south poles of the magnet lies parallel with the Workpiece-supporting face the lines of magnetic flux emanating from magnet poles pass freely through the armature members and through .the soft iron or similar members comprising the workpiece-supporting face, and thence through the wor piece or workpieces placed thereon, the latter bei g thus held firmly in position during the machining or other operation.
On however the magnet being moved angularly through an angle of through the medium of an operating knob, lever or similar device, the magnetic axis will be disposed at right-angles to a plane conte' ring the workpiece-supporting face, and in this position the two armature members will form keepers and provide two flux leakage paths the lines of magnetic flux emanating from the egnet poles, which flux leakage paths are of lou reluctance than that of the path including the soft iron or similar members of the workpiece-supporting face and the workpiece or workpieces mounted thereon, the workpiece-supporting face being thus free or substantially free from magnetic flux, the workpiece or workpieces being consequently capable of removal from the Workholder.
In order that it may be clearly understood and readily carried into effect, the invention is hereinafter described with reference to the accompanying drawing, wherein:
Figure 1 is a plan view of a magnetic workholder constructed in accordance with the present invention;
Figure 2 is a longitudinal vertical section of the same on the line H-II of Figure 1, the workholder being shown in its operative workholding position;
Figure 3 is an end elevation of the same;
Figure 4 is a transverse section on the line IVIV of Figure 2;
Figure 5 is a similar transverse section but showing the workholder in its inoperative position;
Figure 6 is a transverse section on the line VIVI of Figure 2;
Figure 7 is a perspective view of one of the magnets;
Figure 8 is a side elevation of the same;
Figure 9 is a side elevation of a magnet having pole-pieces of tapering form; and
Figures 10 and 11 are sectional views of the invention in a modified form.
The particular workholder illustrated incorporates three permanent magnets of part-cylindrical formation, each of which magnets is so magnetised that its magnetic axis lies at right-angles to the axis of rotation. It will be appreciated however that a plurality of magnets are employed for convenience in manufacture where the production of a comparatively long magnet might present difliculties. Furthermore, by employing magnets of more or less standard length, a workholder of any desired length can be easily manufactured by selecting the appropriate number of magnets and assembling them together on a supporting shaft.
The workholder therefore comprises broadly a casing l composed of non-magnetic material and of box-like form, a workholding surface 2, permanent magnets 3 fixedly mounted on a shaft 4 which is partly rotatable within suitable bearings, and armature members 5 located within the casing in such a position as to provide an alternative path of lower reluctance for the lines of magnetic flux emanating from the magnets when the latter are moved through 90, which lines of magnetic flux would otherwise pass through the workholding surface and workpiece and retain the latter in position. The alternative positions of the magnets and the paths taken by the lines of magnetic flux are shown clearly in Figures 4 and 5, a workpiece being diagrammatically shown in position on the workholding face and indicated by the reference numeral 5.
The fiat workholding surface comprises a series of soft iron or similar magnetic members i separated by intervening non-magnetic spacing members 8, the components being held together by means of non-magnetic bolts or rivets 9, the workholdin surface being finally machined to provide a smooth and flat work-supporting face. As will be clear from Figures 1, i and 5, the components 7 extend throughout the full length and width of the workholder and are of comparatively narrow cross-section, and consequently a workpiece will be effectively maintained in position even though it is situated at the extreme end or lateral edge of the workholding surface, a feature of considerable importance when it is desired to machine a large number of small articles, such as washers or other small components, at one operation.
The casing l is closed at its ends by closure members 10 which carry bearings l I for the shaft i, the bearings being held in position by means of coverplates 12. The shaft and its associated magnets are capable of being moved angularly through i. e. from the position shown in Figure 4 into the position indicated by Figure 5, the shaft being formed with square extremities l3 either of which can receive an operating handle M. A suggested means for limiting pivotal movement is shown in Figure 6, the shaft carrying a plate l5 formed with two notches it either of which may be engaged by a spring-urged plunger H, the plate intermediate the notches, at l8, being of reduced radius, the arrangement being such that with the parts in the position-shown in Figure 6 rotational movement in a clockwise direction will be permitted through 90, whereas anticlockwise movement will be effectively prevented due to the plate being of two different diameters.
The armature members are of laminated formation, as shown clearly in Figure 2, and are composed of a series of soft iron or similar metal stampings riveted or bolted together, as at IS, the armature members being located within the easing by means of securing screws 20. The armature members are held in contact with the workholding surface 2 at its edges by means of securing screws 20a, and are shaped to correspond to the curvature of soft iron or similar pole-pieces 2! on the magnets, a minimum clearance being left between the pole-pieces and armature members when the magnet system is in the operative workholding position, as in Figure 4. The polepieces are of such a length that when the magnet system is in the inoperative position shown in Figure 5, the armature members will overlap the edges of the pole-pieces associated with the north and south poles of the magnets and provide an alternative path for the lines of magnetic flux of shorter length and lower reluctance, the lines of magnetic force naturally taking the path of lower reluctance through the armature members without entering the workholding surface and workpiece. The path taken by the lines of magnetic flux in the operative and inoperative positions of the magnet system is clearly shown in Figures 4 and 5; and it will be observed that in Figure 5 the armature members virtually shortcircuit the magnets, and incidentally perform the function of keepers. It will be appreciated therefore that with the magnet system in the position shown in Figure 5 the workpiece will no longer be attracted to the workholding surface, and consequently can be removed therefrom.
As it is virtually impossible to weld or braze the soft iron pole-pieces to the extremely hard magnet castings, it is necessary to employ some other method of attachment, and in the arrangement shown each pair of pole-pieces are connected together by two plates 22 of brass or other nonferrous metal, which are brazed at their extremities to the edges of the pole-pieces, the noncircular fiat-sided formation of the magnets preventing the pole-pieces turning about the magnets axes.
In order to secure the magnets firmly in position on their associated shaft, non-ferrous members 23 of T shape are mounted in between the magnets, the T-shaped members projecting between the edges of the pole-pieces and being fixed to the shafts by securing screws 24, the magnets being thus keyed in position; the magnets and their associated members 23 being sandwiched in position between annular shoulders 25 one of which may be in threaded connection with the shaft to permit of the magnets being threaded thereon.
Due to the fact that the pole-pieces are always maintained out of contact with their adjacent armature members, the magnet system is capable of being moved from its operative to its inoper ative position, and vice versa, with the minimumof effort, but if desired the effort required may be further decreased by constructing the polepieces of the oppositely-tapering formation shown in Figure 9.
The casing is shown provided with holdingdown feet 26 so that it can be screwed in position on a workbench, but if desired the casing instead of being of the channel section shown may be fitted with a second oppositely-arranged holding surface as indicated at 21 in Figure 10 for engaging a metal workbench 28, or the metal bedplate of a milling machine, or other machine too, so that the work-holder will be secured in position by the holding power of its own magnets. Alternatively, the armature members may be continued downwards as shown at 29 in Figure 11 into a position in which they project from or lie flush with the lower part of the casing I and are therefore capable of contacting any metal surface 28 on which the workholder is placed.
The casing or its associated parts I2 may be provided with some suitable indicator for use in conjunction with the operating handle to indicate whether the parts are in the workholding position or not, and to indicate the direction of permissible movement of the operating handle, and in such a case the extremities of the shaft may be so shaped as to permit of the handle being applied to the shaft in only one position What I claim is:
1. A magnetic work holder comprising a non ferrous casing, a shaft rotatably mounted in said casing, a substantially cylindrical permanent magnet fixed to said shaft, said magnet having diametrically opposite arcuate poles, two armature members spaced from said poles, said armature members being of concave configuration to conform to the shape of said poles, a plurality of soft iron strips extending substantially parallel to said shaft, a plurality of non-ferrous strips alternating with said soft iron strips, all of said strips together providing a work-supporting surface, and supporting means maintaining said strips adjacent respective faces of said two armature members whereby a magnetic circuit including said members, certain of said strips and a work piece supported on said surface may be held in place; and a pair formed, said strips being dimensioned so that a plurality of said soft iron strips register with each of said faces and with the space separating said faces.
2. A magnetic work holder according to claim 1 wherein said supporting means include a pair of soft bars parallel to said strips and enclosing said strips between them, and non-magnetic fastening means securing said bars and said strips together, said bars being flush with said strips and resting directly on the said faces of said armature members, respectively.
3. A magnetic work holder according to claim 1 wherein said permanent magnet comprises a substantially cylindrical body, a pair of arcuate soft iron pole-pieces disjoined from said body, and a pair of non-ferrous plates extending at opposite sides of said body, each of said plates being joined to both of said pole-pieces whereby the latter are held in place.
4. A magnetic work holder according to claim 3 wherein said body has flattened sides extending substantially parallel to the magnetic axis of said body and located diametrically opposite each other, said plates being positioned adjacent said flattened sides, respectively.
5. In a magnetic work holder, in combination, a rotatable shaft; a permanent magnet fixed to said shaft, said magnet comprising a substantially cylindrical body, a pair of arcuate soft iron polepieces disjoined from said body, and a pair of non-ferrous plates extending at opposite sides of said body, each of said plates being joined to both of said pole-pieces whereby the latter are of spaced-apart armature members positioned at opposite sides of said magnet, said members being of concave configuration to conform to the shape of said pole-pieces.
6. The combination according to claim 5 wheret in said body has flattened sides extending substantially parallel to the magnetic axis of said body and located diametrically opposite each other, said plates being positioned adjacent said flattened sides, respectively.
7. The combination according to claim 5 wherein said pole-pieces are of oppositely tapering configuration.
STANLEY ISAIAH HITCHCOCK.
REFERENCES CITED The following references are of record in the file of this patent:
UNITED STATES PATENTS Number Name Date 2,189,524 Randolph et a1 Feb. 6, 1940 2,209,558 Bing July 30, 1940 2,280,437 Levesque Apr. 21, 1942 2,333,230 Beechlyn Nov. 2, 1943 2,347,023 Beechlyn Apr. 18, 1944