Abstract: Apparatus and method for sharpening a cutting tool, such as a kitchen knife. A sharpener has a base unit and one or manual sharpening modules. The base unit has a housing which encloses at least one flexible abrasive disc rotated by an electric motor. Each flexible abrasive disc is adjacent a powered sharpening stage to perform a primary sharpening operation upon the tool. Each manual sharpening module may be removably attachable to the base unit and has a manual sharpening stage that incorporates at least one sharpening element to perform a secondary sharpening operation upon the tool. Each manual sharpening module further has a powered stage guide surface to form a portion of a corresponding powered sharpening stage. When two powered sharpening stages are used, the manual sharpening module(s) can be individually placed between the powered sharpening stages to provide opposing powered stage guide surfaces for each.

Abstract: A green ball grinding method includes the step of supplying a green ball between a first surface of a first member and a second surface of a second member constituting a grinding apparatus, and the step of grinding the green ball between the first surface and the second surface while the green ball rotates around its own axis and in orbital motion. In the step of grinding the green ball, the step of causing the green ball grinding to proceed while applying load between the green ball and each of the first surface and the second surface, and the step of modifying the rotation axis of the green ball by reducing the load lower than in the step of causing the green ball grinding to proceed are executed alternately.

Abstract: The invention relates to an apparatus for the double-sided, grinding machining of flat workpieces with an upper and a lower work disk, each of which has a work surface with a grinding layer, wherein the work surfaces form a work gap amongst themselves, in which workpieces can be ground, wherein at least one of the work disks is rotatably drivable by means of a driving mechanism, and further having a device for guiding the workpieces in the work gap. It is provided according to the invention that debarring means are arranged on at least one of the work disks, which are designed to deburr the workpieces during their machining in the apparatus.

Abstract: A parts carrier assembly for a grinding machine includes an annular parts carrier and a bearing insert. The annular parts carrier includes an upper surface, a lower surface, an inner edge, an outer edge, and a plurality of loading apertures. The inner edge is configured to engage a driving wheel of the grinding machine. The driving wheel rotates about a central axis resulting in rotation of the parts carrier about an offset axis, which is offset from the central axis. The loading apertures are configured to receive parts to be ground by the grinding machine. The bearing insert includes an inner bearing surface complementary in shape to the outer edge of the parts carrier. The outer surface the parts carrier bears against the inner bearing surface of the bearing insert as the parts carrier rotates about the offset axis.

Abstract: The invention relates to a method for machining flat workpieces in a double-sided machining tool, which has an upper and a lower work disk, wherein at least one of the work disks is rotatingly driven and the work disks each have an annular work surface, wherein the work surfaces amongst themselves limit an also annular work gap, in which at least one carrier is located, which guides at least one workpiece in the work gap, so that the at least one workpiece is machined in a double-sided manner between the work surfaces. The distance between the work disks is measured at at least two radially spaced measurement locations of the work gap and in that, from the measured distances, a distance between the work disks is determined at a location of the work gap representing the thickness of the at least one workpiece machined in the work gap.

Abstract: An apparatus, system, and method are provided for reducing edge damage of a disk during chemical mechanical polishing. The apparatus includes a disk carrier configured to receive a disk, the disk having an outside edge and an inside edge, a raised ring adjacent the outside edge of the disk and extending from a surface of the disk carrier to a height greater than a height of the disk, and a raised column adjacent the inside edge of the disk and having a height greater than a height of the disk. The system includes a disk carrier for receiving a disk, a raised ring adjacent the outside edge of each opening, and plugs insertable into a central opening in the disk and having a height greater than a height of the disk. The method includes providing the apparatus, inserting a disk into the apparatus, and polishing the disk.

Abstract: In the double-side polishing apparatus, one end part of a slurry supply hole has a female-tapered face whose inner diameter is gradually increased toward a polishing face of a polishing plate. A pad hole, which corresponds to the slurry supply hole, is formed in a polishing pad covering the slurry supply hole. An edge of the pad hole is located in the slurry supply hole. A fixation pipe, in which a flange section facing the female-tapered face is formed at one end part, is fixed in the slurry supply hole. The edge of the pad hole is sandwiched and held between the female-tapered face of the slurry supply hole and the flange section of the fixation pipe.

Abstract: To propose a method for realizing appropriate delivering of works to carriers in the conventional transfer process. Specifically, in a polishing method for polishing a work retained in a carrier, at least one carrier for retaining a work to be polished is placed between an upper plate and a lower plate; the work is fit in a hole of the carrier; the carrier and the work are inserted between the upper plate and the lower plate; and at least one of the upper plate and the lower plate is rotated while supplying a polishing agent to a space between the upper plate and the lower plate. In fitting the work in the hole of the carrier, an end portion of the work is held and the work is carried to a position above the lower plate; the work is positioned with respect to the hole of the carrier on the lower plate; and the work is released from the hold and guided by a guide to be slowly carried down toward the hole.

Abstract: A wafer unloading system and wafer processing equipment (system) including the same are disclosed. The wafer unloading system includes a fluid supply tube for supplying a fluid, a nozzle for injecting the supplied fluid, and an injection hole defined in a plate to allow the injected fluid to reach a space between a polishing pad and a wafer.

Abstract: A combination sharpener assembly which is particularly useful for fishermen, includes an electrically powered knife sharpener. A manually operated scissors sharpener is mounted in the recess of the housing for the knife sharpener. A hook sharpener is detachably mounted in a compartment in the housing of the knife sharpener. The motor for the knife sharpener is mounted in a sealed inner housing and can be selectively operated under either direct current or alternating current.

Abstract: Disclosed is a semiconductor wafer polishing method for polishing the surfaces to be polished of semiconductor wafers by use of polishing pads (16, 17) provided on fixing plates by relative movement of the polishing pads and the semiconductor wafers held by carriers. The shaping surfaces (25) of a polishing pad shaping jig (21) are shaped by inverting, with respect to ideal shapes, the shapes of the surfaces to be polished of each semiconductor wafer when the surfaces are polished by use of the polishing pads (16, 17) before shaping, and the shapes of the shaping surfaces of the polishing pad shaping jig are transferred to the pad surfaces (16A and 17A) of the respective polishing pads (16, 17). The surfaces to be polished of each semiconductor wafer are polished by use of the pad surfaces.

Abstract: A tool sharpening assembly (100) suitable for sharpening cutting tools (140,350,366,546,562). In some embodiments, a wedge-shaped port is formed between a rotational first abrasive surface (160,262) and a stationary second abrasive surface (162,264) to sharpen a distal cutting edge (146) of a cutting tool (140,230,546). In other embodiments, a cooling mechanism (136,326,330,334,338) actively draws heat generated during a sharpening operation from a tool (140) and through a tool support structure (170,234,328,332) contactingly supporting the tool, in further embodiments, a rotatable abrasive slotted disc (364) comprises at least one inspection aperture (372) formed from an interior sidewall (390) with upper and lower leading and trailing edges (396,398,400,402) of non-uniform separation distance. In other embodiments, a cylindrical drum abrasive member (572) is provided with an associated stationary support plate (574).

Abstract: A knife edge enhancing apparatus includes a support having a support surface and knife blade clamping structure mounted to the support and located above the support surface. An object having a knife edge modifying surface which could be abrasive or non-abrasive is mounted to a holder which is freely slidable on the support surface so that the object surface can be manually moved into contact with a knife edge facet. At least one of the clamping structure and the object surface is angularly adjustable to control the angle of contact of the object surface with the knife edge facet.

Abstract: A method and apparatus for using continuous-loop wires to drive circular flat-surfaced disk-type workholders which are positioned between two opposed upper and lower abrasive-surfaced rotatable platens. Flat-surfaced workpieces are mounted in receptacle openings in the workholders where both surfaces of the workpieces are simultaneously abraded by the two opposed platen that have annular bands of abrasive coatings. The drive wires allow the workholders to be driven at high speeds because of the smooth-action interface between the wires and the circular workholder disks that have circular wire grooves around the peripheries of the workholders. Each workholder assembly consists of a workholder disk, a drive wire, wire idlers, workholder idlers, a wire-tension device, a workholder disk support device and a wire drive motor. The workholder assemblies can be moved away from the platen surface to change platen abrasive disks. Three workholders provide stable three-point support of a floating upper platen.

Abstract: Methods for holding a workpiece with a hydrostatic pad are disclosed herein. The pad includes hydrostatic pockets formed in a face of the body directly opposed to the wafer. The pockets are adapted for receiving fluid through the body and into the pockets to provide a barrier between the body face and the workpiece while still applying pressure to hold the workpiece during grinding. The hydrostatic pads allow the wafer to rotate relative to the pads about their common axis. The pockets are oriented to reduce hydrostatic bending moments that are produced in the wafer when the grinding wheels shift or tilt relative to the hydrostatic pads, helping prevent nanotopology degradation of surfaces of the wafer commonly caused by shift and tilt of the grinding wheels.

Abstract: A polishing apparatus to simultaneously polish both surfaces of a work, and includes a pair of stools rotating in opposite directions, a pair of detecting units to detect rotation rates of the stools, a pressurizing unit to compress the work between the pair of the stools, a slurry supply unit to supply a slurry to the stools, and a control unit to reduce, when determining that a frictional force between the polishing surface and the work exceeds a threshold, at least one of a load applied by the pressurizing unit, the rotation rate of the stools, and a supply amount of the slurry.

Abstract: A bowling ball surface treatment device for abrading, polishing or cleansing a bowling ball includes a housing, a ball displacing unit movably mounted to the housing for holding the bowling ball in a rotatable manner and for reciprocatingly displacing the bowling ball between a temporary waiting region and a surface treatment region, a surface treatment disc for supporting and spinning the bowling ball in the surface treatment region, the surface treatment disc having a surface treatment element for making frictional contact with the bowling ball, a temporary support disc for temporarily supporting the bowling ball in the temporary waiting region when the bowling ball is moved out of the surface treatment region, and a disc drive unit for rotatingly driving the surface treatment disc and the temporary support disc.

Abstract: A bowling ball surface treatment apparatus is designed to uniformly abrade and polish a bowling ball. The apparatus includes a housing and a ball movement guider provided inside the housing for guiding movement of a bowling ball and confining the bowling ball within a limited surface treatment area, and a surface treatment disc arranged below the ball movement guider for supporting, rotating and revolving the bowling ball. The surface treatment disc has a disc shaft and a surface treatment element for abrading or polishing the bowling ball. The apparatus further includes a disc rotating device for rotating the surface treatment disc about a disc center axis and a disc revolving device for rotatably holding the disc shaft of the surface treatment disc and for causing the surface treatment disc to make revolving movement around a sun axis offset from the disc center axis.

Abstract: The invention relates to an apparatus for the double-sided, grinding machining of flat workpieces with an upper and a lower work disk, each of which has a work surface with a grinding layer, wherein the work surfaces form a work gap amongst themselves, in which workpieces can be ground, wherein at least one of the work disks is rotatably drivable by means of a driving mechanism, and further having a device for guiding the workpieces in the work gap. It is provided according to the invention that debarring means are arranged on at least one of the work disks, which are designed to deburr the workpieces during their machining in the apparatus.

Abstract: A hydrostatic pad for use in holding a semiconductor wafer during grinding of the wafer by grinding wheels. The pad includes hydrostatic pockets formed in a face of the body directly opposed to the wafer. The pockets are adapted for receiving fluid through the body and into the pockets to provide a barrier between the body face and the workpiece while still applying pressure to hold the workpiece during grinding. The hydrostatic pads allow the wafer to rotate relative to the pads about their common axis. The pockets are oriented to reduce hydrostatic bending moments that are produced in the wafer when the grinding wheels shift or tilt relative to the hydrostatic pads, helping prevent nanotopology degradation of surfaces of the wafer commonly caused by shift and tilt of the grinding wheels.

Abstract: A workpiece double-disc grinding apparatus including a holder that supports a thin-plate-like workpiece from an outer periphery along a radial direction and is rotatable; a pair of static pressure support members that support the holder from both sides along an axial direction of the rotation thereof in a contactless manner based on a static fluid pressure; and a pair of grinding stones that simultaneously grind both surfaces of a workpiece supported by the holder, in which an interval between the holder and the static pressure support member is not greater than 50 ?m, and the static pressure of the fluid that is not lower than 0.3 MPa. As a result, the workpiece double-disc grinding apparatus and a workpiece double-disc grinding method can stabilize a position of the holder, which can be a cause that degrades a nanotopography of the workpiece in the double-disc grinding for the workpiece.

Abstract: An acrylic polisher includes: a base with two oppositely disposed sideboards with a notch on each of them and a disposition surface in between, a cutting blade set performing a cutting process along the edge of the disposition surface, a stopping board driven by a driving device to move up and downs with respect to the disposition surface. When the stopping board moves downward to the side of the disposition surface, a machining span is formed between the stopping board and the disposition surface. Therefore, as the stopping board lowers to the side of the base, the operator only needs to push an acrylic object toward the stopping board and can quickly obtain the required machining span. The notches on the sideboards of the base form an open space around the disposition surface. The length of the acrylic object is thus not restricted.

Abstract: A knife sharpener comprises a base, a motor, a grinding wheel assembly, a rotary shaft and a spring. The working channel between the edge of the grinding disc and the grinding awl is automatically adjustable to accommodate different blade of different thickness. When the knife sharpener performs grinding operation, the grinding wheel assembly can simultaneously grind both cutting sides of the knife. In addition, the knife can be clamped firmly through the three contacting points of the grinding disc, the grinding awl, and the cutting edge, so that the operation of knife grinding can be successfully performed.

Abstract: A knife sharpener is provided which is capable of precision sharpening of hunting and similar knives that have a first and second blade face, each of which terminates at a facet that meets the corresponding facet to create the knife edge. At least the first of the blade faces has a lower distinct planar or concave section adjacent the edge facet with the lower planar or concave section of the face being set at an angle to the center line of the blade thickness that is different from the angle of the adjoining upper section of the same blade face located adjacent to the back of the blade. The sharpener includes a sharpening member such as one having an abrasive coated surface. The sharpener also includes a planar angle knife guide surface of a knife guide which is designed for intimate sliding and sustaining contact with the second face of the blade in order to position an edge facet on the first of the faces into precise angular relation with the sharpening surface.

Abstract: A bowling ball surface treatment apparatus is designed to uniformly abrade and polish a bowling ball. The apparatus includes a housing and a ball movement guider provided inside the housing for guiding movement of a bowling ball and confining the bowling ball within a limited surface treatment area, and a surface treatment disc arranged below the ball movement guider for supporting, rotating and revolving the bowling ball. The surface treatment disc has a disc shaft and a surface treatment element for abrading or polishing the bowling ball. The apparatus further includes a disc rotating device for rotating the surface treatment disc about a disc center axis and a disc revolving device for rotatably holding the disc shaft of the surface treatment disc and for causing the surface treatment disc to make revolving movement around a sun axis offset from the disc center axis.

Abstract: The double-side polishing apparatus for polishing both faces of a wafer is capable of reliably measuring not only a thickness of an outer part of the wafer but also a thickness of a center part thereof. The double-side polishing apparatus comprises: a lower polishing plate; an upper polishing plate held by a frame; and a carrier having a through-hole for holding the wafer. A window section, through which a laser beam passes, is formed in a part of the upper polishing plate, under which the wafer held by the carrier passes. An optical thickness measuring equipment is provided to a part of the frame, under which the window section passes while the upper polishing plate is rotated. The thickness measuring equipment emits the laser beam through the window section, receives reflected beams reflected from an upper face and a lower face of the wafer, and calculates the thickness of the wafer on the basis of peak values of the reflected beams.

Abstract: The double face polishing apparatus is capable of controlling an amount of supplying slurry to a lower polishing plate. The double face polishing apparatus comprises: a lower polishing plate and an upper polishing plate; a carrier provided between the polishing plates, the carrier having a through-hole for holding a workpiece; a plate driving unit for rotating the polishing plates; a carrier driving unit for rotating the carrier; ring-shaped ducts coaxially provided to the upper polishing plate; a slurry supply source supplying slurry to the ring-shaped ducts; and supply pipes for supplying the slurry to the lower polishing plate. The slurry is supplied to each of coaxial polishing zones of the lower polishing plate via the corresponding ring-shaped ducts and the supply pipes.

Abstract: A surface grinding machine for a sintered rare earth magnetic alloy wafer comprises a pair of disk-shaped grindstones that face each other across a prescribed gap to be rotatable in opposite directions about their center axes. The grinding surfaces of the pair of grindstones and the center axe inclination of one grinding stone are configured to form a planar grinding region A wherein a portion of both of the grinding surfaces of the pair of grindstones lie parallel with a constant intervening gap therebetween. Other portions of the grinding surfaces of the grindstones constitute a wedge-like opening region B that becomes more narrow toward the planar grinding surface A. A feeder to feed the wafers from the wedge-like opening region B toward the planar grinding region A is provided in order to grind both surfaces of the wafers at the planar grinding.

Abstract: A machine for removing sharp edge in plates in general and in glass plates in particular, comprising a frame for the support and advancement of a plate on which there is at least one station for arrissing an edge of the plate, the arrissing station comprising an upper tangential grinding wheel and a lower tangential grinding wheel which have a working profile which is inclined at 45° with respect to the rotation axis of the grinding wheels and can engage respectively an upper edge and a lower edge of the plate being worked.

Abstract: A method for processing a gear set through a lapping operation that includes: providing a lapping machine tool having a first spindle and a second spindle, the second spindle being rotatable about an axis that is generally perpendicular to a rotational axis of the first spindle, the lapping machine tool having a loading zone for loading the first and second spindles; providing a robot with an end effector; loading a first gear set to a first end of the end effector, the first gear set having a ring gear and a pinion gear; moving the first end of the end effector into the loading zone; and loading the first gear set to the lapping machine tool without removing the end effector from the loading zone such that the ring gear is loaded onto the first spindle and the pinion gear is loaded onto the second spindle. An end effector is also provided.

Abstract: Finishing a seal assembly as a unit is proposed, which prevents alignment of the end gaps of the annular body and the annular ring of the seal assembly, provides the ability to manufacture the seal assembly to very low tolerances, and establishes virtually perfect parallelism between the upper and lower surfaces of the seal assembly. A finishing process is characterized by lapping a seal assembly as an assembled unit with a lapper using gritted oil as a polishing medium.

Abstract: A sharpening apparatus with substantially rigid sharpening wheels disposed substantially fixedly on a rotatable drive shaft. An edge of a blade inserted in a slot in the apparatus comes into contact with a sharpening surface on a sharpening wheel. A sliding block associated with that sharpening surface slidably yields to accommodate the inserted blade and applies a force on the blade towards the sharpening surface. The user may selectively adjust force on the blade to achieve more or less sharpening of the edge of the blade. The plurality of sharpening surfaces can offer different levels or degrees of sharpening.

Abstract: A drill bit sharpener includes a motor assembly and a drill bit grinding assembly. The motor assembly has a motor with a drive shaft to drive the drill bit grinding assembly, which includes a driven assembly, a sharpener housing, a grinding wheel assembly and a bit guide assembly. The sharpener housing is attached to the motor assembly, and the grinding wheel assembly is rotatably mounted in the sharpener housing and is rotated by the driven assembly. The bit guide assembly is mounted in the sharpener housing above the grinding wheel assembly. An adjusting screw in the bit guide assembly is used to adjust the grinding wheel assembly relative to the bit guide assembly. Multiple bit guide holes correspond to the grinding wheel assembly are defined in the bit guide assembly and allow a drill bit to pass through to abut the grinding wheel.

Abstract: A metal bond grinding wheel 12 having a horizontal working surface 12a, a holding and rotating means 14 for a workpiece having a horizontal supporting surface 14a opposite to said working surface 12a, a voltage applying means 16 having the metal bond grinding wheels and an electrode 16a installed oppositely to the working surfaces in an uncontacted state and applying a pulsed voltage between them, a grinding fluid feeding means 18 for feeding an electroconductive grinding fluid to the working surfaces are installed.

Abstract: In order to take a ground work W out of a work-holding hole of a carrier by chucking the outer periphery of the work W, a surface grinding machine is provided with chucking means for chucking the outer periphery of the work W by a plurality of claw members and a plurality of cutouts into which the claw members of the chucking means can be inserted are made in the edge of the work-holding hole of the carrier, and the ground work W in the work-holding hole is taken out at the position of the cutouts.

Abstract: A versatile ultrahoned sharpener includes a stop assembly which contains an inner hardened structure such as being made from metal or ceramic to serve as a positive limiting stop if the knife being sharpened cuts excessively into the plastic stop assembly of the sharpener. The sharpener also includes a manually actuated abrasive surfaced unit for cleaning or shaping the surface of at least one of the sharpening wheels in the sharpener. The sharpener further includes various bearing structures for effectively mounting the motor driven shaft which rotates the abrasive coated disks of the sharpener.

Abstract: A sphere grinding apparatus (1) for grinding spheres by two discs consisting of a rotational disc (5) and a stationary disc (6), the sphere grinding apparatus (1) incorporating: a central shaft (3) slidable in an axial direction; and a housing (4) for rotatively supporting the central shaft (3), wherein the rotational disc (5) is joined to the central shaft (3) and the stationary disc (6) is joined to the housing (4). Accordingly, it is possible to provide a sphere grinding apparatus which is capable of improving a machining accuracy and which has a simple structure and the cost of which can be reduced.

Abstract: An improved process for lapping a surface according to the present invention comprises:a) providing a work piece with two surfaces to be lapped,b) providing two rotatable platens, each having i) a back surface and ii) a front surface,c) providing a sheet of abrasive material having an abrasive face and a back side, the back side being on the front surface of each of the two rotatable platens with the abrasive faces of each sheet facing the other sheet,d) placing the work piece with two surfaces to be lapped between the two rotatable platens, so that each abrasive face faces only one of the two surfaces to be lapped,e) rotating the two platens at a rotational speed of at least 500 revolutions per minute,f) contacting each of the abrasive faces with the only one of the two surfaces to be lapped, andg) lapping said two surfaces of said work piece simultaneously.

Abstract: A sphere polisher capable of making uniform conditions under which balls are polished is provided. The inner and outer polishing circuits are defined by the grooves 23 provided on the rotative disc 10 and the fixed disc 20. The storage conveyor 50 is provided with an outer ball guiding passage 55 and an inner ball guiding passage 56. The ball supply chute 57 is provided with the inner chute portion 57a connecting the inner polishing circuits with the outer ball guiding passage 55, and the outer chute portion 57b connecting the outer polishing circuits with the inner ball guiding passage 56. The ball discharge chute 58 is provided with the inner discharge chute portion 58a connecting the inner polishing circuits with the inner ball guiding passage 56, and the outer discharge chute portion 58b connecting the outer polishing circuits with the outer ball guiding passage 57.

Abstract: A method for polishing a semiconductor wafer is provided. A semiconductor wafer is detached from a polishing pad on a side of an upper polishing plate and is kept to be supported by a lower polishing plate. A contact area between the a wafer and the upper polishing plate is set to be less than a contact area between the wafer and the lower polishing plate. As a result, the wafer is definitely detached from the polishing pad on the side of the upper polishing plate and is to be kept supported by the lower polishing plate when the upper polishing plate is lifted.

Abstract: In a polishing machine for polishing parts between a table and an upper polishing head, the upper polishing head includes push rods to clear the workpieces after a polishing operation. A push ring engages the push rods as a polishing head is being raised, holding the workpieces in position on the table.

Abstract: A knife sharpener (1) having a flexible grinding system includes a grinding wheel (2) and means for rotating the wheel, and has a fixed guide surface (14) for roughly positioning a knife for sharpening. A movable member (21) is disposed adjacent to the grinding member (17) of the grinding wheel, with the movable biased by a spring (26) in a direction towards the wheel. In operation, when a knife is moved into contact with the grinding wheel, the movable member is displaced inwardly to reduce the contact pressure such that only the knife edge contacts the wheel. Thus, rather than recontouring the knife edge, the knife edge is most closely returned to its original contour. Using such a flexible grinding system substantially maintains the original edge contour of the blade.

Abstract: A high speed knife sharpening apparatus where the surface of a first rotating abrasive element is that of a truncated cone and forms a first facet with microgrooves and a microburr. A second stage is a novel composite cone shaped honing wheel made up of a micro abrasive imbedded in an epoxy matrix. The honing wheel refines the edge developed in the first stage, into an erect triangular shape with a radius of curvature, at the apex (edge), of typically several microns or less depending on the hardness of the knife steel. A unique blade holding system constrains the blade to a precisely defined angle relative to each of the grinding (first) and honing (second) stages. Proportionately larger grinding forces are developed for thicker knife blades, thus sharpening times are approximately the same over the common range of knives from small paring knives (6"), large chef's knives (10") up to kitchen cleavers.

Abstract: A grinding apparatus has a tool support radially offset from a workpiece axis, rotatable about a support axis radially offset from and substantially parallel to the workpiece axis, and having a forwardly axially directed front support face formed at the support axis with an axially forwardly projecting centering formation formed a forwardly convex and part-spherical end surface. An annular grinding tool centered on a tool axis has an annular axially forwardly directed grinding surface engaging the workpiece surface and an axially backwardly directed rear tool face axially confronting the front support face and formed centered on the tool axis with an axially backwardly open recess engaging the end surface of the projection and of part-spherical shape complementary to the projection end surface. This tool is spaced from and out of direct contact with the support except at the recess and projection end surface.