GEM FACETING MACHINE
United States Patent 3818641
A gem stone faceting machine is provided in which a dop stick holder, secured coaxially on a facet spacing shaft which forms part of a dividing head, has capacity for vertical bodily adjustment, for horizontal oscillation, for fore and aft rocking movement, and for rotary adjustment about its own axis. With reference to fore and aft rocking, a precision level is provided, stable in any indicating position, which tilts in unison with the dop stick holder, and which serves as a visual guide for consistently limiting the cutting of facets which are intended to have identical slopes to fine tolerances which are so exact as to be different in kind from any tolerances which have heretofore been available. With reference to rotary or facet spacing adjustment of the dividing head, and corresponding adjustment of the gem stone, a conventional index gear is provided having a number of teeth which is equal to, or a multiple of, the number of facet cutting positions desired. Instead of a single, fixed scale required to be used for all cuts available with that gear, I provide separate, substitutable scale plates, each having a single, marginal scale, and each with only those markings which are required for the particular job in hand.
US Patent References:
Gem holder for grinding machines
Rakowitzky - February 1951 - 2542704
Method of and device for producing specifically oriented polished faces on diamonds
Grodzinski - October 1953 - 2654979
Machine for grinding and polishing gem facets
Collar - January 1957 - 2779138
Grinding and polishing machine for precious or semi-precious stones
Malin - July 1963 - 3098327
Gem holder for grinding machines
Rakowitzky - February 1951 - 2542704
Method of and device for producing specifically oriented polished faces on diamonds
Grodzinski - October 1953 - 2654979
Machine for grinding and polishing gem facets
Collar - January 1957 - 2779138
Grinding and polishing machine for precious or semi-precious stones
Malin - July 1963 - 3098327
Application Number:
05/256817
Publication Date:
06/25/1974
Filing Date:
05/25/1972
View Patent Images:
Export Citation:
Primary Class:
Other Classes:
451/389
International Classes:
B24B9/16; B24B9/06; B24B9/16
Field of Search:
51/165.75,229,125.5
Primary Examiner:
Whitehead, Harold D.
Claims:
I claim
1. A gem stone faceting machine having, in combination,
2. A gem stone faceting machine having, in combination,
3. A gem stone faceting machine as set forth in claim 2 in which the uniformity of facet slope level is of the tube and bubble type with the tube of arcuate form and having a radius so large that uniformity of facet slope to within a few seconds of arc is dependably obtainable.
1. A gem stone faceting machine having, in combination,
2. A gem stone faceting machine having, in combination,
3. A gem stone faceting machine as set forth in claim 2 in which the uniformity of facet slope level is of the tube and bubble type with the tube of arcuate form and having a radius so large that uniformity of facet slope to within a few seconds of arc is dependably obtainable.
Description:
This invention relates to gem stone grinding and polishing machines.
The faceting of gem stones is a demanding operation because
1. The material dealt with is usually extremely valuable material which must not be wasted or ruined; and
2. The requirements for faceting of high quality are exacting.
It is important, therefore, that the operative be a person of responsibility and skill, and that he be provided with equipment which is precise, reliable, easy to understand and easy to use correctly.
The conventional faceting machine includes a motor driven lap which revolves about a vertical axis and has an upper, horizontal working face. On the lap, or on interchangeable laps of this kind, all grinding and polishing operations are performed.
On the same base alongside the lap, a stand is provided which includes an elevator and an elevator operating screw, the elevator being manually oscillatable about the axis of the screw.
A frame is mounted on the elevator with freedom for rocking movement about a horizontal axis, the elevator and frame including, respectively, a reference mark and a coarse protractor scale for guidance of the operator.
The frame carries a facet spacing shaft for adjustive rotation about an axis which intersects the frame axis at right angles to the latter. A dop stick is removably mounted on the facet spacing shaft in coaxial relation therewith, by means of a chuck.
Angular adjustment of the frame controls the facet slope. Rotary adjustment of the facet spacing shaft controls the angular disposition of the facets about the axis of the shaft, and hence about the axis of the gem stone.
The facet spacing shaft has fixed upon it an index gear which may be set and locked in various predetermined, mechanically controlled angular positions by a locking device on the frame. The index gear is equipped with index means for the guidance of the operator. Adjustment of the index gear controls the angular disposition of the facets about the axis of the dop-stick-held gem stone.
The even spacing of like crown facets about the axis of the gem stone is precisely, mechanically controlled by angular settings of the index gear which is fast on the facet spacing shaft. The means provided in the conventional machine for guiding the operating in selecting these settings is adequate but awkward and undependable.
The slope of a facet changes as the cutting proceeds. The operator watches the declination scale and terminates the operation when the scale indicates to him that the desired angle has been attained. Some machines are provided with an adjustable stop which limits the downward movement of the dop arm. The first facet of a series is cut to the desired depth, the stop is set at that point, and the rest of the series cut down to the same stop. This is an imprecise procedure.
After the crown is finished the gem stone is re-dopped with the aid of a V block, to reverse it end for end, and the pavilion facets are similarly cut.
The conventional machine, as outlined above, has two grave defects which it is the purpose of the present invention to remedy.
The first of these is that the setting for facet slope is coarse, being governed by a 90° scale generally having a radius of only about 11/2 inches, so that each degree space is minute, measuring a little more than 1/40 of an inch and a little less than 2/3 of a millimeter. As the cutting proceeds, the operator watches the 90° scale and terminates the operation when he judges, on the basis of inexact information, that the desired slope has been attained. Seemingly minute errors can produce grave deficiencies, throwing edges out of line, varying their lengths, and mislocating edge terminal points.
The difficulty is not serious if all the corresponding facets have exactly the same slope, even if that slope deviates somewhat from the intended slope. It is want of consistency which shows up importantly as defective execution.
I have contrived a means for essentially eliminating want of consistency.
To this end, I have adjustably mounted a precision level vial on the supporting shaft of the declination frame as a permanent part of the machine to turn in unison with the frame. This level vial, disposed in a vertical plane, includes a glass tube having an upwardly convex arcuate bore of such large radius, for example, that 1 minute of arc measures 2 millimeters. With the declination frame set so that the reading on the 90° scale appears to be correct, the level is placed in its neutral or zero position on the shaft, and a set screw is tightened to fix the level relative to the shaft and to the 90° scale. In cutting main facets, the first of a series is cut to the desired depth and slope. The level is then adjusted to an index mark on the vial while the facet contacts the lap. The bubble of the level is watched as the subsequent grinding proceeds, and each remaining facet of the series is ground down to a point at which the bubble attains the same index. The terminal point is approached cautiously in each instance and one or more static readings of the level at a marked point on the lap are desirably taken for each facet. The tube of the level has index marks at 2 millimeter intervals. Uniformity to within a small fraction of 1 minute or arc is virtually assured. In the conventional machine the slope can, at best, be duplicated to 1/10 of a degree, or 6 minutes of arc. With my improvement, duplication to within 2 to 3 seconds of arc is definitely attainable. The precision is improved approximately 180 fold.
When all the facets of like slope have been ground, these facets are polished. If this requires substitution of a thicker or a thinner lap, the level is consulted in readjusting the height of the elevator.
Uniform spacing of the facets about the gem stone axis demands that the index gear have a number of teeth equal to, or a multiple of, the number of facets in each set of like facets.
The facet spacing shaft of the conventional machine similarly has fast upon it an index gear having a number of teeth which is equal to, or a multiple of, the number of facet settings required for a particular cut.
There are two types of cut that constitute at least 90 per cent of all faceting; to-wit, the standard brilliant cut and the step or emerald cut. Each of these cuts requires only 32 operating positions. The 96 tooth index gear is conventionally used for these cuts. The head, including this gear, has a scale of 96 divisions with every sixth division numbered 6, 12, 18, 24, etc., and the other marked divisions unnumbered.
It is very confusing to cut a brilliant gem of 32 divisions on a head with 96 index gear teeth and 96 divisions marked, but five of every six divisions unnumbered, because it is necessary to keep tab on the concerned 32 divisions, half of which are unnumbered.
The eight main facets would be cut at 12, 24, 36, etc. The eight stars would come halfway between at 6, 18, 30, 42, etc. The 16 girdle facets would be cut at 3, 9, 15, 21, 27, etc. This requires great care and concentration on the part of the operator.
In accordance with the present invention, this difficulty is overcome by providing a separate, marginally graduated scale plate for each situation, and by providing means for removably securing each scale plate in approproate position to the face of the indexing gear. For 32 divisions only eight positions are numbered settings for main facets. Each numbered division is halved and quartered. Star facets are cut on the half marks and girdle facets on the quarters. With this system a brilliant can be cut without reference to numbers for all facets excepting the mains.
Other objects and advantages will hereinafter appear.
In the drawing forming part of this specification,
FIG. 1 is a view in side elevation of an illustrative, practical and advantageous faceting machine embodying features of my invention;
FIG. 2 is a fragmentary view showing how the angular disposition of the faceting arm changes progressively as the grinding of a facet proceeds;
FIG. 3 is a fragmentary front view showing the indexing gear, and an index disc adapted for cutting 32 facets, and associated with a 96 tooth index gear;
FIG. 4 shows a substitutable indexing disc adapted for 96 cuts and usable with a 96 tooth indexing gear; and
FIG. 5 is a sectional view through the index gear and associated parts, taken on the line 5--5 of FIG. 3, in the direction of the arrows.
The illustrative machine 10 as seen in FIG. 1 comprises an electric motor driven lap 12 which is fast with the upper end of a vertical drive shaft 14 and has an upper, horizontal working surface 16.
A fixed, adjacent, channeled table 18 supports and guides the base 20 of a stand 22 directly toward and from the lap. The stand 22, in addition to the channel-fitting base 20, comprises a standard 24 and an overhanging rigid beam 26.
An elevator operating screw 25 is seated on a bearing in the base 20, has bearing in the beam 26, and is provided at its upper end with an operating wheel 28 upon which an upstanding handle 30 is fixed.
An elevator 32 has the elevator operating screw 25 threaded through it. The elevator may be adjusted as to height by holding it against rotation while turning the screw. The elevator may be fixed at any desired level and made oscillatable in unison with the screw 25 by means of a set screw 34 which has a cross handle 36.
The elevator is a bifurcated structure whose arms rotatatively support horizontal bearing shafts 38, 38 of a tiltable frame 40. The frame 40 rotatively supports a facet spacing shaft 42 for movement about an axis which intersects the axis of the shafts 38, 38 at right angles. The facet spacing shaft 42 carries at its outer end a chuck 44 in which a gem stone carrying dop stick 46, having a gem stone 48 affixed to it, may be clamped. The construction is such that the dop stick necessarily extends in coaxial relation to the shaft 42. Hence, the gem stone is co-axial with the shaft.
The shaft 42 also has fast upon it an index gear 50 which may be adjusted to, and locked in, various predetermined angular positions about the axis of shaft 42 for determining the angular locations of the facets about the axis of the gem stone. The frame 40 carries a locking lever 52 which is rockable upon a cross pivot pin 54. The locking lever 52 is formed with at least one tooth which may be inserted in any desired tooth space of the gear 50 for securing the gear, and consequently the gem stone, in a fixed angular position about the axis of the shaft 42 as a center. The locking lever can be rocked clear of the gear to permit adjustment of the gear from one faceting position to another. A knurled set screw 56 is disposed directly over the locking arm of the lever 52 and may be turned in one direction to force the lever 52 down into locking position, and in the opposite direction to free the arm for withdrawal from locking position. The reference locking tooth of the lever 52 may serve as an index for determining the orientation of the gear 50, and hence of the gem stone.
Up to this point, the structure as described in detail does not differ essentially from conventional practice.
It is a significant feature of the invention that the gear 50 is made on its forward face to include a concentric circumferentially threaded boss 57 of larger diameter than the outside of the chuck 44. Distinct scale plates 58a and 58b are provided, each having a marginal scale. These scales have, respectively, 32 divisions and 96 divisions, each appropriate for use with a 96 tooth gear. A knurled ring 60 is threaded onto the boss for clamping the selected scale plate against the face of the gear. When 96 distinct settings are required, the plate 58b is used, and when 32 distinct settings are required, the plate 58a is used.
The gear 50 is adapted to be replaced by a gear of the same diameter with a different number of teeth, and for use with such a gear suitable distinct scale plates of appropriate spacing can be provided. The 32 position scale plate 58a may also be used with a 64 tooth gear. On each scale plate shown every fourth division is numbered, and halves and quarters are distinctively marked but not numbered. The principle may, of course, be extended to provide scale plates suitable for use with other gears. With an 80 tooth gear, for example, a scale plate would be provided having 20 major divisions marked and numbered, with halves and quarters indicated but unnumbered.
The control of the angular disposition of the facet spacing shaft 42 with reference to the axis of shaft 38 is a matter of primary importance, not only because it controls the actual slope of the facets, but also the consistency of slope of related facets.
The shaft 38 as in the conventional machine, has fast upon it a 90° scale plate 62 which turns in unison with the declination frame 40. The scale plate 62 is cooperative with an index mark 64 on the elevator. The scale plate has a radius of the order of 11/2 inches, so that 1° covers only a little more than 1/40 of an inch or a little less than 2/3 of a millimeter.
During the cutting of a facet, the declination of the faceting shaft increases, and the operator is required to determine at what point of declination the operation should be terminated. The scale plate 62 is inadequate for securing the required consistency of facet slope.
In accordance with the invention a level carrying arm 66 is mounted on the shaft 38 with freedom for rotation relative to the shaft. A knurled set screw 68, threaded through the hub of the lever carrying arm 66, may be tightened to fix the arm in any desired angular position relative to the shaft.
A level 70, carried by the arm 66, is a permanent part of the machine. It is of a well known precision type, never previously used in this connection. The bore of the level is made arcuate, being formed precisely upon an arc of very large radius, illustratively upon a radius so great that an arc of 1 minute covers 2 millimeters of circumference.
With the declination of shaft 42 held at the desired angle as indicated by the scale plate 62, the level carrying arm is set, through loosening and retightening of the set screw 68, so that the level indicates a level condition and is fixed in that relationship to the shaft 38. This relationship of level to shaft and scale is maintained throughout the cutting of all facets of a set of corresponding slope.
If the circle of which the level forms a segment were completed it would occupy a vertical plane, with its center far below the small arcuate segment formed by the level itself.
As the cutting of a facet progresses, the bubble of the level remains at one end of the level tube until approximately the last two and one-half minutes of tilting, i.e., with the center of the bubble about two and a half minutes of arc removed from the level position.
By watching the bubble of the level in relation to index marks of the level, itself, the facet forming operation may be terminated for each facet when the bubble of the level indicates zero on the level. This assures the hitherto unattainable and revolutionary result that all of the involved facets of a group will be within a small fraction of 1 minute of arc, of identical slope. As previously indicated, the precision of slope is increased 180 fold as compared with reference to the protractor 62.
Each group of facets required to have substantially identical slopes is similarly dealt with.
An important function of this level is in changing from the last grinding lap to a polishing lap. It is extremely important that the gem facet lie perfectly flat on the polishing lap as it did on the last grinding lap. Due to difference in thickness of laps, adjustment in the height of the head must be made. To do this, the bubble is set on an index mark on the vial with the facet contacting the grinding lap. After changing to the polishing lap, the bubble is made to take the same index position by raising or lowering the head. With only ordinary care the facet can be made to duplicate its position on the two laps to within two or three seconds of arc.
The terms "horizontal" and "vertical" are generally used herein in a relative sense for bringing out clearly the relation of the parts to one another. Where the level is concerned, however, the terms are absolute. The entire organization as shown and described, for example, could be tilted in any direction without contradicting these terms as they are used herein.
I have described what I believe to be the best embodiment of my invention. What I desire to secure by letters patent is set forth in the following claims.
The faceting of gem stones is a demanding operation because
1. The material dealt with is usually extremely valuable material which must not be wasted or ruined; and
2. The requirements for faceting of high quality are exacting.
It is important, therefore, that the operative be a person of responsibility and skill, and that he be provided with equipment which is precise, reliable, easy to understand and easy to use correctly.
The conventional faceting machine includes a motor driven lap which revolves about a vertical axis and has an upper, horizontal working face. On the lap, or on interchangeable laps of this kind, all grinding and polishing operations are performed.
On the same base alongside the lap, a stand is provided which includes an elevator and an elevator operating screw, the elevator being manually oscillatable about the axis of the screw.
A frame is mounted on the elevator with freedom for rocking movement about a horizontal axis, the elevator and frame including, respectively, a reference mark and a coarse protractor scale for guidance of the operator.
The frame carries a facet spacing shaft for adjustive rotation about an axis which intersects the frame axis at right angles to the latter. A dop stick is removably mounted on the facet spacing shaft in coaxial relation therewith, by means of a chuck.
Angular adjustment of the frame controls the facet slope. Rotary adjustment of the facet spacing shaft controls the angular disposition of the facets about the axis of the shaft, and hence about the axis of the gem stone.
The facet spacing shaft has fixed upon it an index gear which may be set and locked in various predetermined, mechanically controlled angular positions by a locking device on the frame. The index gear is equipped with index means for the guidance of the operator. Adjustment of the index gear controls the angular disposition of the facets about the axis of the dop-stick-held gem stone.
The even spacing of like crown facets about the axis of the gem stone is precisely, mechanically controlled by angular settings of the index gear which is fast on the facet spacing shaft. The means provided in the conventional machine for guiding the operating in selecting these settings is adequate but awkward and undependable.
The slope of a facet changes as the cutting proceeds. The operator watches the declination scale and terminates the operation when the scale indicates to him that the desired angle has been attained. Some machines are provided with an adjustable stop which limits the downward movement of the dop arm. The first facet of a series is cut to the desired depth, the stop is set at that point, and the rest of the series cut down to the same stop. This is an imprecise procedure.
After the crown is finished the gem stone is re-dopped with the aid of a V block, to reverse it end for end, and the pavilion facets are similarly cut.
The conventional machine, as outlined above, has two grave defects which it is the purpose of the present invention to remedy.
The first of these is that the setting for facet slope is coarse, being governed by a 90° scale generally having a radius of only about 11/2 inches, so that each degree space is minute, measuring a little more than 1/40 of an inch and a little less than 2/3 of a millimeter. As the cutting proceeds, the operator watches the 90° scale and terminates the operation when he judges, on the basis of inexact information, that the desired slope has been attained. Seemingly minute errors can produce grave deficiencies, throwing edges out of line, varying their lengths, and mislocating edge terminal points.
The difficulty is not serious if all the corresponding facets have exactly the same slope, even if that slope deviates somewhat from the intended slope. It is want of consistency which shows up importantly as defective execution.
I have contrived a means for essentially eliminating want of consistency.
To this end, I have adjustably mounted a precision level vial on the supporting shaft of the declination frame as a permanent part of the machine to turn in unison with the frame. This level vial, disposed in a vertical plane, includes a glass tube having an upwardly convex arcuate bore of such large radius, for example, that 1 minute of arc measures 2 millimeters. With the declination frame set so that the reading on the 90° scale appears to be correct, the level is placed in its neutral or zero position on the shaft, and a set screw is tightened to fix the level relative to the shaft and to the 90° scale. In cutting main facets, the first of a series is cut to the desired depth and slope. The level is then adjusted to an index mark on the vial while the facet contacts the lap. The bubble of the level is watched as the subsequent grinding proceeds, and each remaining facet of the series is ground down to a point at which the bubble attains the same index. The terminal point is approached cautiously in each instance and one or more static readings of the level at a marked point on the lap are desirably taken for each facet. The tube of the level has index marks at 2 millimeter intervals. Uniformity to within a small fraction of 1 minute or arc is virtually assured. In the conventional machine the slope can, at best, be duplicated to 1/10 of a degree, or 6 minutes of arc. With my improvement, duplication to within 2 to 3 seconds of arc is definitely attainable. The precision is improved approximately 180 fold.
When all the facets of like slope have been ground, these facets are polished. If this requires substitution of a thicker or a thinner lap, the level is consulted in readjusting the height of the elevator.
Uniform spacing of the facets about the gem stone axis demands that the index gear have a number of teeth equal to, or a multiple of, the number of facets in each set of like facets.
The facet spacing shaft of the conventional machine similarly has fast upon it an index gear having a number of teeth which is equal to, or a multiple of, the number of facet settings required for a particular cut.
There are two types of cut that constitute at least 90 per cent of all faceting; to-wit, the standard brilliant cut and the step or emerald cut. Each of these cuts requires only 32 operating positions. The 96 tooth index gear is conventionally used for these cuts. The head, including this gear, has a scale of 96 divisions with every sixth division numbered 6, 12, 18, 24, etc., and the other marked divisions unnumbered.
It is very confusing to cut a brilliant gem of 32 divisions on a head with 96 index gear teeth and 96 divisions marked, but five of every six divisions unnumbered, because it is necessary to keep tab on the concerned 32 divisions, half of which are unnumbered.
The eight main facets would be cut at 12, 24, 36, etc. The eight stars would come halfway between at 6, 18, 30, 42, etc. The 16 girdle facets would be cut at 3, 9, 15, 21, 27, etc. This requires great care and concentration on the part of the operator.
In accordance with the present invention, this difficulty is overcome by providing a separate, marginally graduated scale plate for each situation, and by providing means for removably securing each scale plate in approproate position to the face of the indexing gear. For 32 divisions only eight positions are numbered settings for main facets. Each numbered division is halved and quartered. Star facets are cut on the half marks and girdle facets on the quarters. With this system a brilliant can be cut without reference to numbers for all facets excepting the mains.
Other objects and advantages will hereinafter appear.
In the drawing forming part of this specification,
FIG. 1 is a view in side elevation of an illustrative, practical and advantageous faceting machine embodying features of my invention;
FIG. 2 is a fragmentary view showing how the angular disposition of the faceting arm changes progressively as the grinding of a facet proceeds;
FIG. 3 is a fragmentary front view showing the indexing gear, and an index disc adapted for cutting 32 facets, and associated with a 96 tooth index gear;
FIG. 4 shows a substitutable indexing disc adapted for 96 cuts and usable with a 96 tooth indexing gear; and
FIG. 5 is a sectional view through the index gear and associated parts, taken on the line 5--5 of FIG. 3, in the direction of the arrows.
The illustrative machine 10 as seen in FIG. 1 comprises an electric motor driven lap 12 which is fast with the upper end of a vertical drive shaft 14 and has an upper, horizontal working surface 16.
A fixed, adjacent, channeled table 18 supports and guides the base 20 of a stand 22 directly toward and from the lap. The stand 22, in addition to the channel-fitting base 20, comprises a standard 24 and an overhanging rigid beam 26.
An elevator operating screw 25 is seated on a bearing in the base 20, has bearing in the beam 26, and is provided at its upper end with an operating wheel 28 upon which an upstanding handle 30 is fixed.
An elevator 32 has the elevator operating screw 25 threaded through it. The elevator may be adjusted as to height by holding it against rotation while turning the screw. The elevator may be fixed at any desired level and made oscillatable in unison with the screw 25 by means of a set screw 34 which has a cross handle 36.
The elevator is a bifurcated structure whose arms rotatatively support horizontal bearing shafts 38, 38 of a tiltable frame 40. The frame 40 rotatively supports a facet spacing shaft 42 for movement about an axis which intersects the axis of the shafts 38, 38 at right angles. The facet spacing shaft 42 carries at its outer end a chuck 44 in which a gem stone carrying dop stick 46, having a gem stone 48 affixed to it, may be clamped. The construction is such that the dop stick necessarily extends in coaxial relation to the shaft 42. Hence, the gem stone is co-axial with the shaft.
The shaft 42 also has fast upon it an index gear 50 which may be adjusted to, and locked in, various predetermined angular positions about the axis of shaft 42 for determining the angular locations of the facets about the axis of the gem stone. The frame 40 carries a locking lever 52 which is rockable upon a cross pivot pin 54. The locking lever 52 is formed with at least one tooth which may be inserted in any desired tooth space of the gear 50 for securing the gear, and consequently the gem stone, in a fixed angular position about the axis of the shaft 42 as a center. The locking lever can be rocked clear of the gear to permit adjustment of the gear from one faceting position to another. A knurled set screw 56 is disposed directly over the locking arm of the lever 52 and may be turned in one direction to force the lever 52 down into locking position, and in the opposite direction to free the arm for withdrawal from locking position. The reference locking tooth of the lever 52 may serve as an index for determining the orientation of the gear 50, and hence of the gem stone.
Up to this point, the structure as described in detail does not differ essentially from conventional practice.
It is a significant feature of the invention that the gear 50 is made on its forward face to include a concentric circumferentially threaded boss 57 of larger diameter than the outside of the chuck 44. Distinct scale plates 58a and 58b are provided, each having a marginal scale. These scales have, respectively, 32 divisions and 96 divisions, each appropriate for use with a 96 tooth gear. A knurled ring 60 is threaded onto the boss for clamping the selected scale plate against the face of the gear. When 96 distinct settings are required, the plate 58b is used, and when 32 distinct settings are required, the plate 58a is used.
The gear 50 is adapted to be replaced by a gear of the same diameter with a different number of teeth, and for use with such a gear suitable distinct scale plates of appropriate spacing can be provided. The 32 position scale plate 58a may also be used with a 64 tooth gear. On each scale plate shown every fourth division is numbered, and halves and quarters are distinctively marked but not numbered. The principle may, of course, be extended to provide scale plates suitable for use with other gears. With an 80 tooth gear, for example, a scale plate would be provided having 20 major divisions marked and numbered, with halves and quarters indicated but unnumbered.
The control of the angular disposition of the facet spacing shaft 42 with reference to the axis of shaft 38 is a matter of primary importance, not only because it controls the actual slope of the facets, but also the consistency of slope of related facets.
The shaft 38 as in the conventional machine, has fast upon it a 90° scale plate 62 which turns in unison with the declination frame 40. The scale plate 62 is cooperative with an index mark 64 on the elevator. The scale plate has a radius of the order of 11/2 inches, so that 1° covers only a little more than 1/40 of an inch or a little less than 2/3 of a millimeter.
During the cutting of a facet, the declination of the faceting shaft increases, and the operator is required to determine at what point of declination the operation should be terminated. The scale plate 62 is inadequate for securing the required consistency of facet slope.
In accordance with the invention a level carrying arm 66 is mounted on the shaft 38 with freedom for rotation relative to the shaft. A knurled set screw 68, threaded through the hub of the lever carrying arm 66, may be tightened to fix the arm in any desired angular position relative to the shaft.
A level 70, carried by the arm 66, is a permanent part of the machine. It is of a well known precision type, never previously used in this connection. The bore of the level is made arcuate, being formed precisely upon an arc of very large radius, illustratively upon a radius so great that an arc of 1 minute covers 2 millimeters of circumference.
With the declination of shaft 42 held at the desired angle as indicated by the scale plate 62, the level carrying arm is set, through loosening and retightening of the set screw 68, so that the level indicates a level condition and is fixed in that relationship to the shaft 38. This relationship of level to shaft and scale is maintained throughout the cutting of all facets of a set of corresponding slope.
If the circle of which the level forms a segment were completed it would occupy a vertical plane, with its center far below the small arcuate segment formed by the level itself.
As the cutting of a facet progresses, the bubble of the level remains at one end of the level tube until approximately the last two and one-half minutes of tilting, i.e., with the center of the bubble about two and a half minutes of arc removed from the level position.
By watching the bubble of the level in relation to index marks of the level, itself, the facet forming operation may be terminated for each facet when the bubble of the level indicates zero on the level. This assures the hitherto unattainable and revolutionary result that all of the involved facets of a group will be within a small fraction of 1 minute of arc, of identical slope. As previously indicated, the precision of slope is increased 180 fold as compared with reference to the protractor 62.
Each group of facets required to have substantially identical slopes is similarly dealt with.
An important function of this level is in changing from the last grinding lap to a polishing lap. It is extremely important that the gem facet lie perfectly flat on the polishing lap as it did on the last grinding lap. Due to difference in thickness of laps, adjustment in the height of the head must be made. To do this, the bubble is set on an index mark on the vial with the facet contacting the grinding lap. After changing to the polishing lap, the bubble is made to take the same index position by raising or lowering the head. With only ordinary care the facet can be made to duplicate its position on the two laps to within two or three seconds of arc.
The terms "horizontal" and "vertical" are generally used herein in a relative sense for bringing out clearly the relation of the parts to one another. Where the level is concerned, however, the terms are absolute. The entire organization as shown and described, for example, could be tilted in any direction without contradicting these terms as they are used herein.
I have described what I believe to be the best embodiment of my invention. What I desire to secure by letters patent is set forth in the following claims.