US3835589A

US3835589A - Centerless grinding fixture for synthetic crystal rods and the like

Info

Publication number: US3835589A
Application number: US00286549A
Authority: US
Inventors: E Silverman
Original assignee: Individual
Current assignee: Individual
Priority date: 1972-09-06
Filing date: 1972-09-06
Publication date: 1974-09-17
Anticipated expiration: 1991-09-17

Abstract

A centerless grinding fixture for grinding rough, out of round rods to roundness and predetermined dimension by a grinding wheel, the fixture and wheel being movable relative to each other in a plane transversely of the rod. A rod support roll, a base support for the roll, a guide member extending longitudinally above the roll and below the grinding wheel for resiliently contacting the rod and capable of reacting away from the rod for altering the pattern of feed of the rod past the grinding wheel, carrying means for the guide member adjustable by a screw member along an axis making an acute angle of between 40* to 50* with a plane containing the axes of the grind wheel and roll whereby the guide member may be moved downwardly relative to the roll and inwardly relative to said plane to effect trueing of the rod and a reduction in its size while maintaining said resilient contact of the guide member with respect to the rod in a tangent plane substantially paralleling said plane through the axes of the grinding wheel and roll. Supporting means for the carrying means mounted on the roll support and which may be pivoted about the axis of the roll for adjusting said acute angle.

Description

United States Patent Silverman [451 Sept. 17, 1974 CENTERLESS GRINDING FIXTURE FOR SYNTHETIC CRYSTAL RODS AND THE LIKE [76] Inventor: Emanuel Silverman, 14401 Hartsook, Oak Park, Mich. 91403 Filed: Sept. 6, 1972 Appl. No.: 286,549

[56] References Cited UNITED STATES PATENTS 2,569,873 10/1951 Stacey ..5l/165.75X

Primary ExaminerI-larold D. Whitehead Attorney, Agent, or FirmSidney A. Ochs [57] ABSTRACT A centerless grinding fixture for grinding rough, out of round rods to roundness and predetermined dimension by a grinding wheel, the fixture and wheel being movable relative to each other in a plane transversely of the rod. A rod support roll, a base support for the roll, a guide member extending longitudinally above the roll and below the grinding wheel for resiliently contacting the rod and capable of reacting away from the rod for altering the pattern of feed of the rod past the grinding wheel, carrying means for the guide member adjustable by a screw member along an axis making an acute angle of between 40 to 50 with a plane containing the axes of the grind wheel and roll whereby the guide member may be moved downwardly relative to the roll and inwardly relative to said plane to effect trueing of the rod and a reduction in its size while maintaining said resilient contact of the guide member with respect to the rod in a tangent plane substantially paralleling said plane through the axes of the grinding wheel and roll. Supporting means for the carrying means mounted on the roll support and which may be pivoted about the axis of the roll for adjusting said acute angle.

12 Claims, 4 Drawing Figures SPAIENKDSEH 7 m4 SHEET 1 OF 2 UH xix PAIENTEB SE? I 1 m4 SHEEI 2 BF 2 CENTERLESS GRINDING FIXTURE FOR SYNTHETIC CRYSTAL RODS AND THE LIKE BACKGROUND OF THE INVENTION This invention relates to a centerless grinding fixture or apparatus operable in conjunction with a grinding wheel for grinding rough and out of round rods to true cylindrical form and predetermined dimension. It is especially directed to apparatus of this character for grinding synthetic crystal rods.

Conventional centerless grinders are designed for the grinding of materials such as tough metals having good elastic properties. They are not suitable to produce true cylindrical rods from brittle materials such as rods of crystals of ruby or sapphire, for example, which have even been ground by hand to a rough approximation of final dimension. These rods have fiat planes, are out of round, and even misshapen. When placed in a conventional centerless grinding such rods usually crack when the grinder picks up a high spot or other irregularity.

A principal object of the invention is to provide centerless grinding apparatus capable of obviating the foregoing problem and which is capable of grinding rough and out of round rods of brittle materials such as synthetic crystals and the like to true roundness or cylindrical form.

A further object is to provide a centerless grinding fixture of the character of the preceding object capable of grinding rods to predetermined size and which covers a wide range of sizes.

A specific object is to provide a centerless grinding fixture of the character of the preceding objects featuring a guide member for resiliently contacting the rod and capable of reacting away from the rod and altering the pattern of feed of the rod to thus inhibit breakage.

Another specific object is to provide a centerless grinding fixture of the character of the preceding objects featuring a micromatic feed and wherein the guide member is in contact with the crown of the curve of the rod nearest to it during all reductions in the size of the rod.

The above and other objects, features and advantages attending the present invention will be understood from a consideration of the description of a preferred embodiment of the invention following the accompanying DESCRIPTION OF THE DRAWINGS Wherein FIG. 1 is a side elevational view partly in section showing the apparatus of the invention.

FIG. 2 is a top view of apparatus of the invention shown in FIG. 1, parts being in section or broken away.

FIG. 3 is a sectional view taken at A--A of FIG. 1; and

FIG. 4 is an enlarged sectional view taken at BB of FIG. 2.

Referring to the drawings the apparatus of a preferred form of my invention comprises a main base or base support generally referred to by the numeral 10, comprising a bottom wall 12 of generally rectangular shape, a pair of opposite

upstanding side walls

14 and 16 extending longitudinally of the bottom wall 12 and connecting therewith, an upstanding end wall 18 connecting the

walls

14 and 16 and bottom wall and a further short upstanding wall 20 spaced from the wall 18 and connecting with the

side walls

14 and 16 and bottom wall 12. As seen from FIGS. 1 and 2 the

walls

14, 16, 18 and 20 form a pocket 22 to receive a hard refractory wheel or roll 24 such as a Norton rubberceramic wheel A80-RR51 which is to support the synthetic crystal rod 26 shown in phantom in FIG. 2 which is to be reduced in size for example to that of a rod 28 during the grinding operation by a grinding wheel 30. The roll 24 is supported by the base 10, through a shaft 32 which is journalled in precision roller bearings 34 located in the

walls

14 and 16. The roll 24 is fixed to the shaft 32 in any suitable manner. For instance it may have a hub 36 through which it is pinned to the shaft and which serves to locate the roll between the walls l4, 16. The roll 24 is rotatably driven by a timing pulley 38 pinned to shaft 32 which in turn is driven through a timing belt 40 from a timing pulley 42 of a drive motor 44. The grinding wheel 30 may be that of a surface grinder (not shown) on the table of which the base 10 may be secured as by bolting (not shown).

The grinding wheel 30 as seen in FIG. 1, is preferably arranged directly above the support roll 24 with the axes of rotation of both in a common vertical plane XX. They are spaced apart vertically a distance such that they form an entrance nip 45 smaller at the plane XX than the initial size of rod 28 such that the initial contact of roll 24 and wheel 30 is beyond the peripheral crests of these members where they intersect the plane XX. The roll 24 and wheel 30 must have the same direction of rotation but different speeds. In the illustrated embodiment both the roll 24 and wheel 30 are driven in a clockwise direction looking at FIG. 1. The roll 24 may, for example, have a diameter of 4 inches and be driven at 50 rpm and the wheel 30 may have a diameter of 7 inches and be driven at 3,600 rpm. Such a combination imparts rotation to the rod 26 yet enables grinding to take place.

An important feature of the invention is the feed and guide assembly generally referred to by the numeral 50 which comprises a guide member generally referred to by the numeral 52, extending longitudinally of the roll 24 and above and adjacent the roll for contacting and guiding the rod 26 during grinding, an adjustable carrying means generally referred to by numeral 54 and an adjustable supporting means for the carrying means 54 generally referred to by the numeral 56 secured to the main support 10. As evident from FIG. 3 the means 54 and 56 form a dovetail slide assembly with each other of which the means 54 is the movable part of the slide and the means 56 is the stationary part.

The carrying means 54 comprises a generally Z shape sectioned element or carriage 58 extending the length of roll 24 and radially thereof. It has a stem portion 60 of generally rectangular section, a lateral wing 62 at the lower end of the stem extending at an obtuse angle to the stem providing a horizontal face 64 for supporting the guide member 52 and has a further lateral wing 66 at the upper end of the stem projecting downwardly from the stem 60 at right angles thereto. The wing 66 carries an adjustment screw assembly generally referred to by the numeral 68.

Attached to the lower face 70 of the stem portion 60 by screws 72 is a plate 74 of regular trapezoidal section which is slidable in a slideway 76 formed as seen in FIG. 3 by two spaced rails 78, 80 and a rectangular sectioned block 82 of the adjustable supporting means 56.

The rails 78, are secured to the block 82 by spaced screws 84 of which one only is shown. The block 82 is rigidly secured to the main base 10 through an arm 86 having a hub portion 88 joumalled on a needle bearing 90 on the shaft 32 of the roll 24 thus permitting swinging movement or adjustment of the block 82 and arm 86 about the axis of the roll 24. The block 82 is attached to an outer end portion 92 of arm 86 by two screws 94. The arm 86 in turn has a lateral wing 96 by which it is rigidly connected to the inner face 98 of the upstanding wall 16 of the support base 10 through a locking bolt 100. The wing 96 has an elongated arcuate slot 102 through which the bolt extends by which the arm 86 and hence the block 82 is provided with limited swinging adjustment about the axis of roll 24 to a predetermined angle 0 prior to commencing grinding.

The guide member 52 comprises an elongated platelike element 1 10 extending longitudinally of the roll 24, and having a lateral edge face 112 facing the rod 26, formed of hard carbide for contacting the rod 26. The guide member is secured to the face 64 of carrying means 54 by two shouldered studs 114 and 116. The stud 114, which is located adjacent the front end 118 of the guide member is fitted in the element so as to provide a pivot around which the guide member may swing and adjust the relationship of the edge face 112 to the rod to a small angle R seen in FIG. 2, usually about one degree. The element 110 is provided with an elongated slot 120 at the second or rearwardly located stud 116 to facilitate the adjustment and other swinging movement of the plate. In order to provide a fine adjustment for the guide member and a resilient abutment for its edge face 112 with respect to the rod 26 the element 110 includes an upstanding ear 122 preferably located between the studs 114, 116 through which projects with clearance the threaded shank of an adjustment screw 124 threadedly received in the stern portion 60 of the carrying means 54. The stem portion 60 is also counterbored as at 126 to provide a seat for one end of a compression spring 128 surrounding the screw 124, the other end of the spring abutting the car 122 so as to urge or bias the guide member toward the rod 26 to the limit providing by the screw 124. By rotating the screw 124 the aforesaid adjustment of the guide member may be obtained. Moreover any unusual pressure against the guide member as may be caused by a high spot on the rod 26 will enable the guide member to momentarily move away from its preferred position with the spring 128 returning it to normal position after the spot is removed. Under some conditions it may be desired to lock the guide member in a fixed adjusted position. For this purpose a lock screw 130 is provided.

Operation of the carrying means 54 through its slide assembly with the supporting means 54 to effect a downward and inward movement of the guide member 52 with respect to the rod 26 is accomplished by the adjustment screw or micrometer assembly 68. The assembly 68 comprises as best seen in FIGS. 1 and 4 a rotatable shaft the lower portion of which is provided with a screw thread 142 which threadedly engages in the block 82 of the supporting means 56. Pinned as at 144 to the upper end of the shaft is a knurled control knob or head 146 having a hollow extension 148 which is rotatably carried on a rigid shouldered bearing sleeve 150 in which the shaft 140 also rotates which sleeve is fixedly mounted in a bore 152 of the wing 66 of the carrying means 54. Rotatably mounted on the extension 148 of the knob 146 is a micrometer thimble 154 provided with a circumferential dial seen in FIGv 1, provided with a zero reference line and divided into a plurality of divisions each representing an amount in thousandths of an inch to be removed from the rod 26. Adjacent the thimble 154 and pinned as at 156 to the wing 66 of the carrying means 54 slide carriage 58 is a barrel 158 carrying a zero reference line and a ten division Verner scale. Thimble 154 is releasably secured to the knob 146 by a set screw 160 so that it may have its zero line set opposite the zero line of the barrel 158 at any position of screw 142 and guide member 52. A spacing collar 162 pinned as at 164 inhibits axial movement of the shaft 140. It will be evident that rotation of the knob 146 and hence the screw shaft 140 will cause axial movement of carrying means 54 and a vertical and horizontal change in the position of the guide member 52.

In order to prevent breakage of rods if for some reason they are shifted to the rear side of roll 24 where they would drop off the roll, the invention provides a guard member secured by screws 172 to the top of wall 18 of the base support 10. It has a lateral section 174 projecting to a point short of the nip of the roll 24 and wheel 30 and which extends longitudinally of the roll 24 to inhibit the above referred to shifting of the rod. Slots 176 pennit adjustment.

It will be observed that with the angular positioning of the screw 142 and associated slide mechanism of the carrying means 54 that the guide member will have forward and downward components of movement for each turn of the screw. If the screw has a right hand thread a counter clockwise rotation of control knob 146 looking at FIG. 2 will be required to produce these movements. If the thread be a left hand thread an opposite or clockwise rotation of the knob 146 will be required to produce the same result.

In operation of the fixture of this invention the fixture is clamped on the table of a surface grinder so that the centerline or axis of the support roll 24 is directly under the centerline or axis of the grinding wheel 30 and with the axes of the roll 24 and wheel 30 parallel to each other. Moreover the wheel 30 will preferably be positioned as seen in FIG. 3 midway the length of roll 24, since it provides a greater distance of support for the rod past the wheel during feeding. This positioning of the grinding wheel is not critcal. The wheel may if desired be at any other position, for example further rearwardly as seen in phantom in FIGS. 2 and 3.

Let it now be assumed that a rod such as the rod 26 shown in phantom in FIG. 1, is to be ground down to a rod the size of the rod 28 in this figure. As seen the rod is placed on the roll 24 to the left of the plane XX an optimum distance, for instance 3/8 of an inch, from the plane XX, to obtain maximum roundness in grinding. The guide member 52 having been previously moved outwardly away from the roll 24 is now brought into position such that its edge face 112 touches the end of rod 26 at a position below the wheel 30 at the intersection of the rod periphery and a horizontal plane through the axis of the rod. With the locking screw 130 released the guide member 52 is then swingably adjusted around pivot 114 by the screw 124 so that its edge face 112 forms an angle R, as seen in FIG. 2, in the order of 1 or 2 with a plane paralleling plane X-X and with the open end of the angle to the front end of the roll 24 and wheel 30 as also seen in FIG. 2. With the support roll 24 and grinding wheel 30 rotating in the directions shown, the wheel will then be lowered into contact with the rod and grinding initiated. The rod 26 will pass under the grinding wheel 30 from front to rear designated in FIG. 2 at a rate determined by the angle R of the guide member and speed of roll 24 and by the setting of the grinding wheel 30.

The characteristic of this type of grinding is such that the axis of the rod 26 must be offset from the plane XX an optimum distance D and generally maintained if a perfectly round rod is to be obtained. This distance may readily be determined after a few spot checks of rods which have been ground using the subject apparatus. For rods about 1 inch and under a distance D of approximately 3/8 inch has been found to produce satisfactory results.

Assuming that this distance has been properly chosen, the feed and guide assembly 50 provides a convenient means by which the distance D can be maintained while simultaneously providing improved dimensional accuracy in the grinding operation.

Thus as the rod 26 is to be reduced in diameter to that of rod 28 for example from 1 inch to 1/2 inch the guide member 52 must be moved both vertically and horizontally to the new position represented by the rod 28. This new position may be obtained by lowering the guide member 52 through the screw 142 and slide carriage mechanism 60 vertically an amount equal to onehalf the distance of vertical travel of grinding wheel 30. This movement is not critical since the same contact of guide member 52 is generally maintained throughout. However due to changes in the points of contact of the roll 24, wheel 30 and the rod in going from 1 inch to l/2 inch a rod 28 exactly l/2 inch may not result for a reading on the grinder indicating removal of l/4 inch of stock or a vertical movement of H2 inch. The difference may be in order of several thousandths of an inch. To compensate for this shift in the points of contact an optimum angle of setting of the assembly 50 is selected and the thimble divisions are graduated based on this setting and the pitch of the screw 142 to indicate actual stock removal from the rod. To cover all settings of the assembly 50 an adjustment of angle 0 between 40 to 50 is provided.

As previously stated a feature of the invention is its ability to produce cylindrical rods from brittle material such as ruby or sapphire which have been ground by hand to a rough approximation to the final diameter. These rods have flat planes, high spots and are out of round. When placed in a regular centerless grinder such rods usually crack when the grinder picks up a high spot. With the spring reactive guide member of the present invention such breakage is inhibited. Thus when the rod passes under the grinding wheel and the high spot is large enough the rod will cause the guide member to react and move into a position parallel with the support roll 24. In this case the rod will no longer feed under and past the grinding wheel. Moreover if the spot is sufficiently high the guide member will react to a reverse angle in which case the rod, instead of feeding through will move away (backwards) from the grinding wheel. As it moves back, the guide member under its spring bias will return toward its normal position so that the rod will again move forward. Several forward and reverse movements may result until the grinding wheel reduces the spot to the point where the rod can complete its passage under and past the grinding wheel. Thus this system constitutes an automatic control that prevents the grinding wheel from placing too much pressure on brittle materials such as ruby and other crystal materials and glass. Once a round rod is produced the guide member 52 may be locked in normal position, if desired, and further fine grinding of the rod completed.

From the foregoing description of the invention it will be evident that a novel centerless grinding fixture particularly suited for the grinding of synthetic crystal rods has been provided which is capable of inhibiting breakage and producing round and accurately dimensioned rods. It will be understood that various changes and modifications will occur to those skilled in the art without departing from the spirit and intent of the invention and all such changes, modifications and equivalent applications and structures are contemplated as come within the purview of the following claims.

What is claimed is:

1. In a grinding machine for the centerless grinding of brittle rods to a predetermined size and circular section, a grinding fixture for receiving the rods for grinding, a table to which the fixture is secured and a rotatable grinding wheel disposed above said table, said grinding wheel and table being movable relative to each other for effecting engagement of the grinding wheel with said rods, and said fixture comprising a rotatable roll for supporting the rods during grinding, base support means carried by the table for supporting said roll, a guide member positioned for engaging the rods, carrying means for carrying said guide member, resilient means acting between the guide member and carrying means for normally resiliently holding the two in a predetermined relationship and providing a reactive cushion for the guide member during grinding, said guide member extending from said carrying means in a direction toward a plane containing the axes of the roll and grinding wheel and being positioned for engaging the rod surface being ground in the region of the rod between the regions where the rod is engaged by the grinding wheel and the roll and such that the axis of the rod is intermediate said guide member and said plane and said grinding wheel having such a direction of rotation during grinding as to urge the rod toward said guide member, supporting means for said carrying means extending from said base support means, and mechanical means operably coacting between said carrying means and said supporting means and extending in a direction generally radially of the axis of said roll and at an angle to said plane and guide member, said mechanical means by a single operation thereof and independently of said resilient means movably and fixedly adjusting said carrying means on said supporting means, during the grinding operation in said direction generally radially of and toward the axis of said roll and simultaneously therewith through said carrying means and independently of said resilient means movably and fixedly adjusting said guide member both inwardly toward said plane and laterally toward said roll and base support means while in contact with the rod surface being ground in effectuating successive reductions in the size of the rod to produce a rod of said predetermined size and of substantially true circular section.

2. A grinding machine as claimed in claim 1 wherein said carrying means is movable by said mechanical means in a plane forming an angle of approximately 40 to 50 to said plane containing the axes of said roll and grinding wheel.

3. A grinding machine as claimed in claim 1 wherein said carrying means is movable by said mechanical means in a plane forming such an angle to said plane containing the axes of said roll and grinding wheel whereby with the guide member in contact with the said surface of the rod being ground where it intersects the same diametral line therethrough, the axis of the rod following each of successive reductions in the size thereof by the grinding wheel will be at substantially the same predetermined distance from said plane containing the axes of said roll and grinding wheel.

4. A grinding machine as claimed in claim 1 wherein said carrying means is movable by said mechanical means in a plane forming such an angle to said plane containing the axes of said roll and grinding wheel whereby with the guide member in contact with the said surface of the rod being ground where it intersects the same diametral line through the axis of the rod, a tangent to the point of contact of the rod and roll is substantially the same following each of successive reductions in the size of the rod by the grinding wheel.

5. A grinding machine as claimed in claim 1 wherein said mechanical means comprises a screw type member axially confined and freely rotatable in said carrying means and threadedly received in said supporting means whereby rotation of said screw member will effect said adjustment of said carrying means and guide member and wherein the guide member extends longitudinally of the roll and comprises a lateral edge presented to the said surface of the rod being ground and is adjustable on its carrying means such that such edge face forms an acute angle with said plane containing the axes of said roll and grinding wheel and diverges from said plane from a point adjacent to a second plane containing the circumference of said grinding wheel.

6. A grinding machine as claimed in claim 1 wherein the guide member comprises a generally horizontal plate-like portion having a lateral edge face presentable to said surface of the rod being ground and a longitudinal end adjacent which it is pivotally mounted on its carrying means for swinging movement in the direction in which said guide member is adjustable by said mechanical means and wherein said resilient means associated with said guide member and carrying means biases said lateral edge toward said rod.

7. A grinding machine as claimed in claim 6 including screw means for adjusting the angular position of said lateral edge face of said guide member relative to said surface of the rod being ground and stop means for limiting the swinging movement of said plate-like portion.

8. A grinding machine as claimed in claim 2, wherein about the axis of the rotatable support roll and wherein there are means operable between said supporting means and the base support means for said roll for adjustably locking said supporting means in a predetermined position facilitating said angular positioning of said mechanical means.

10. A grinding machine as claimed in claim 1 wherein the guide member carrying means comprises a slide element operable in a slideway on said supporting means and wherein said mechanical means comprises a screw member rotatably mounted on said slide element on an axis forming an acute angle of between forty to fifty degrees with said plane containing said axes of said roll and grinding wheel and threadedly engaged with said supporting means and adapted upon rotation of said screw member to move said slide element along said angular axis whereby the guide member may be accorded said inward and lateral movement to enable grinding of the rod to a predetermined size, and wherein said screw has an operating head rotatable therewith and carries a releasable cylindrical indexing ring having a plurality of divisions demarked thereon on the periphery thereof the total of which represents the pitch of the screw and wherein the slide element carries a fixed zero and vernier ring coaxial with said screw member and axially in juxtaposition to said indexing ring,

11. A centerless grinding fixture for use with a grinder in the centerless grinding of brittle rods to a predetermined size and circular section, said grinder having a work table to which the fixture is to be secured and a grinding wheel disposed above said table, said grinding wheel and table being movable relative to each other for effecting engagement of the grinding wheel with said rods, said fixture comprising a rotatable roll for supporting the rod during grinding, base support means for supporting said roll, a guide member positioned for engaging the surface of the rod being ground in the region of the rod between the regions where the rod is engaged by the grinding wheel and the roll and such that the axis of the rod is intermediate said guide member and a plane containing the axes of the roll and grinding wheel, said guide member extending laterally toward said plane and said grinding wheel having such a direction of rotation as to urge the rod toward said guide member, carrying means for said guide member, resilient means acting between said guide member and carrying means for normally resiliently holding the two in a predetermined relationship and providing a reactive cushion for the guide member during grinding, supporting means for said carrying means extending from said base support means, said carrying means being mounted on said supporting means for sliding movement thereon in a second plane at an angle to said plane containing the axes of the roll and grinding wheel, an adjustment screw rotatably mounted on said carrying means, said screw being confined on said carrying means against axial movement and having a threaded portion received in a mating threaded bore in said supporting means whereby rotation of said adjustment screw will produce a fixedly sliding adjustment of said carrying means and guide member carried thereby relative to said surface of the rod being ground in the direction of said plane containing the axes of said roll and grinding wheel and independently of said resilient means when effecting reductions in the size of the rod, an operating head on said able on said supporting means forms an angle of between 40 to 50 with said plane containing the axes of said roll and grinding wheel and wherein said guide member is simultaneously moved toward said latter plane while maintaining substantially the same diametral point of contact with said surface of said rod in successive reductions in the size of the rod.

Claims

2. A grinding machine as claimed in claim 1 wherein said carrying means is movable by said mechanical means in a plane forming an angle of approximately 40* to 50* to said plane containing the axes of said roll and grinding wheel.

8. A grinding machine as claimed in claim 2, wherein said mechanical means comprises an adjusting screw rotatably mounted and axially confined on the carrying means for the guide member and threadedly engaged in the supporting means for said carrying means, for effecting said adjustment of said carrying means and guide member and rotatable vernier means associated with said screw and carrying means.

9. A grinding machine as claimed in claim 8 wherein the supporting means for said guide member carrying means is pivotally mounted for swinging movement about the axis of the rotatable support roll and wherein there are means operable between said supporting means and the base support means for said roll for adjustably locking said supporting means in a predetermined position facilitating said angular positioning of said mechanical means.

10. A grinding machine as claimed in claim 1 wherein the guide member carrying means comprises a slide element operable in a slideway on said supporting means and wherein said mechanical means comprises a screw member rotatably mounted on said slide element on an axis forming an acute angle of between forty to fifty degrees with said plane containing said axes of said roll and grinding wheel and threadedly engaged with said supporting means and adapted upon rotation of said screw member to move said slide element along said angular axis whereby the guide member may be accorded said inward and lateral movement to enable grinding of the rod to a predetermined size, and wherein said screw has an operating head rotatable therewith and carries a releasable cylindrical indexing ring having a plurality of divisions demarked thereon on the periphery thereof the total of which represents the pitch of the screw and wherein the slide element carries a fixed zero and vernier ring coaxial with said screw member and axially in juxtaposition to said indexing ring.

11. A centerless grinding fixture for use with a grinder in the centerless grinding of brittle rods to a predetermined size and circular section, said grinder having a work table to which the fixture is to be secured and a grinding wheel disposed above said table, said grinding wheel and table being movable relative to each other for effecting engagement of the grinding wheel with said rods, said fixture comprising a rotatable roll for supporting the rod during grinding, base support means for supporting said roll, a guide member positioned for engaging the surface of the rod being ground in the region of the rod between the regions where the rod is engaged by the grinding wheel and the roll and such that the axis of the rod is intermediate said guide member and a plane containing the axes of the roll and grinding wheel, said guide member extending laterally toward said plane and said grinding wheel having such a diRection of rotation as to urge the rod toward said guide member, carrying means for said guide member, resilient means acting between said guide member and carrying means for normally resiliently holding the two in a predetermined relationship and providing a reactive cushion for the guide member during grinding, supporting means for said carrying means extending from said base support means, said carrying means being mounted on said supporting means for sliding movement thereon in a second plane at an angle to said plane containing the axes of the roll and grinding wheel, an adjustment screw rotatably mounted on said carrying means, said screw being confined on said carrying means against axial movement and having a threaded portion received in a mating threaded bore in said supporting means whereby rotation of said adjustment screw will produce a fixedly sliding adjustment of said carrying means and guide member carried thereby relative to said surface of the rod being ground in the direction of said plane containing the axes of said roll and grinding wheel and independently of said resilient means when effecting reductions in the size of the rod, an operating head on said adjustment screw, a releasable indexing ring on said head having a plurality of divisions demarked thereon the total of which represents a predetermined axial advance of the screw and of movement of the guide member toward said rod, and a vernier ring coaxial with said adjustment screw and axially in juxtaposition to said indexing ring.

12. A grinding fixture as claimed in claim 11, wherein said second plane in which said carrying means is slidable on said supporting means forms an angle of between 40* to 50* with said plane containing the axes of said roll and grinding wheel and wherein said guide member is simultaneously moved toward said latter plane while maintaining substantially the same diametral point of contact with said surface of said rod in successive reductions in the size of the rod.