FIELD OF THE INVENTION

This invention relates to a method and apparatus for chamfering a glass substrate used for manufacturing of information recording media including hard disk drives (HDDs).

BACKGROUND OF THE INVENTION

There has been an increasing need for information recording media with increase capacity such as ability to store larger amount of data. In order to fulfill such need, a glass substrate nowadays is preferred over a conventional aluminum alloy substrate. The downside of the glass substrate, which is usually machined into a disk shape with a circular hole in the center, is that it is prone to cracking, breaking. As a result it contributes to higher quantity of defect glass or no good (NG) glass. Thus, in a glass substrate manufacturing, chamfering to even out the edges (outer and inner edges) is an essential step.

In a conventional glass substrate manufacturing process, a step of chamfering of a glass substrate occurs after a step of coring, but prior to a step of lapping.

Japanese Patent Application Publication No. 2000-107995 disclosed a grinding method in which the glass substrate is positioned onto a chamfering machine and is fixed to a position via a vacuum means. The chamfering machine rotates in a grinding manner simultaneously grinding the inner and peripheral edges of the substrate. At the completion of the chamfering process, the substrate is subjected to further lapping and polishing to reach a predetermined level of smoothness and thickness.

The disadvantage of the known method is that as the glass substrate is grinded, glass chips occur and remain on a chamfering machine. Thus, the remaining glass chips cause scratching on the face of the next and subsequent glass substrate being introduced onto the chamfering machine. This problem has not been recognized in the past as the glass substrate is prepared with high thickness and the conventional manufacturing of glass substrate tends to have high stock removal. Thus, any scratch marks on the substrate are eventually eliminated in the polishing process. However, preparing a raw glass substrate with high thickness require higher quantity of melted glass while high stock removal will take longer polishing time all of which contribute to higher manufacturing cost. Further, the current trend of the HDD technology allows the disk to spin even faster than before. Therefore, a slightly thicker glass disk is preferred. This means that high stock removal is no longer an option as a means for removing scratch marks on the face of the glass substrate.

US Patent No. 7,798, 889 B2 disclosed a chamfering apparatus of which includes a grindstone having a cylindrical hollow end portion, a grind stone driving unit that rotates the grindstone around an axis of the cylindrical hollow end portion, a substrate rotation- driving unit that rotates the glass substrate around either one of an axis of the outer periphery and an axis of the center circular hole; and a pressing unit that presses the grindstone to the glass substrate such that an annular end face of the grindstone contacts with an edge of either one of the outer periphery and the inner periphery of the glass substrate while the cylindrical hollow end portion of the grindstone face with one of the outer periphery and the inner periphery of the glass substrate. However, there is still a need for a chamfering apparatus, method and manufacturing process that efficiently reduce scratching cause by glass chips. SUMMARY OF THE INVENTION

It is an object of the present invention to provide an apparatus and method for chamfering glass substrate for use in the manufacturing of information recording medium. The apparatus helps reducing scratches on the glass substrate causes by the glass chips derived during the chamfering process. Reducing scratching during chamfering in turns reduces stock removal and ultimately lower production cost.

In one aspect of the invention, there is provided an apparatus for chamfering glass substrate, more specifically those glass substrate for manufacturing information recording medium including Hard Disk Drives (HDDs). In one embodiment, the apparatus comprising a single clamp jig. The clamp jig has a circular-shaped body with a center circular hole. The clamp face adapted to receive a glass substrate introduced thereon. The apparatus includes a means to operable securing the glass substrate onto the clamp jig while chamfering is in progress and releasing the glass substrate at the end of the chamfering cycle.

In another embodiment, apparatus further comprising a second clamp jigs. The first clamp jig is mounted on a fixed mounting plate in the same manner as with the earlier embodiment. Both the first and the second clamp jigs have a circular hollow body corresponding to a glass substrate with a center circular hole. The second clamp jig is adapted to move down and clamp the glass disk between the first and the second clamp jigs and move up when each chamfering cycle is completed releasing the glass disk from the clamping so that the chamfered glass disk can be transported out of the first clamp's face. The apparatus further comprise a means for cleaning the face of the first and second clam jigs. In another aspect of the invention, there is provided a method for chamfering glass substrate. The method comprising a step of cleaning a clamp jig to remove glass chips at the end of each chamfering cycle prior to starting the next chamfering cycle. The method uses pressurized fluid in which a stream of pressurized fluid is directed toward the face of the clamp jig wherein the pressurized fluid sweep across the face of the clamp jig removing any glass chips remain on the face of the clamp jig.

In a further aspect of the invention, the invention provides a method for manufacturing of a glass substrate for use in manufacturing of information recording media. The method comprising a novel chamfering process according to one of the aspects of the present invention. BRIEF DESCRIPTION OF DRAWINGS

The objects, features and advantages of the principles of the invention will be better understood by following the detail description of the invention with accompanying drawings which illustrate the principles described herein and are a part of the specification. Fig. 1 shows a schematic diagram explaining chamfering process and an embodiment of the chamfering apparatus according to the principle of the present invention;

Fig. 2 shows a schematic diagram of an embodiment of the apparatus for chamfering according to the principle of the present invention;

Fig. 3 shows a schematic diagram explaining a further embodiment and a method for cleaning the face of claim jigs forming part of the chamfering process according to the principle of the invention;

Fig. 4 shows a schematic diagram explaining the method of chamfering according to the principle of the present invention; and

Fig. 5 shows a flow chart illustrating a method for manufacturing a glass substrate for use in manufacturing of information recording medium according to the principle of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the principles of the present invention. It will be apparent, however, to one skilled in the art that the present principles may be practiced without these specific details. Reference in the specification to "an embodiment," "an example" or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment or example is included in at least that one embodiment, but not necessarily in other embodiments. The various instances of the phrase "in one embodiment" or similar phrases in various places in the specification are not necessarily all referring to the same embodiment. The present invention discloses an apparatus and method for chamfering glass substrate use for the manufacturing of information recording medium including hard disk drives (HDDs).

In a manufacturing of glass substrate for the manufacturing of informing recording medium such as HDDs, chamfering occurs after a step of coring. The purpose of chamfering is to smooth out the outer as well as inner peripheral edges of the glass substrate, for example a glass disk in order to avoid cracking of the glass substrate when subject to further step of treatment along the course of production such as lapping and polishing. During the chamfering process, the grindstone cause the glass to chip away, thus make the glass edges smoother. However, at the end of each cycle of the chamfering, the glass chips remains on the chamfering machine, such as on the clamp faces. The glass chips, then causes scratching of the next glass substrate being introduce onto the chamfering machine.

The present invention provides an apparatus 10 for chamfering glass substrate, for example, a glass substrate 12 with a center circular hole for the manufacturing of Hard Disk Drives (HDDs).

Fig. 1 shows a schematic diagram explaining the principle and embodiment of the chamfering apparatus 10 with clamp jigs being contaminated with glass chips, a root cause of scratching of the glass substrate 12, and a solution of removing such contaminants from the clamp face proposed by the present invention.

Fig. 2 shows an embodiment of the chamfering apparatus 10 according to the present invention. In this embodiment, the apparatus 10 comprising only one clamp jig. The embodiment comprising a first clamp jig 15, a cylindrical grindstone 35, a grindstone 45, a cleaning means 50 and a securing means (not shown). The prefer features and characteristic of each element will be further discussed in the description of the second embodiment of the apparatus discussed below. Fig 3 shows a second embodiment of the apparatus in which the apparatus further comprising a second clamp jig 20.

As shown in Figs. 1 , 2, 3 and 4, the first clamp jig 15 has a hollow circular shape corresponding to a disk-shaped glass substrate 12 (glass disk) and with a size corresponding to the size of the glass disk such that the center circular hole on the glass disk is overlaid on the circular hollow of the first clamp jig 15. The first clamp jig 15 is mounted on a fixed mounting plate (not shown) and communicates to a driving unit driving (not shown) the fist clamp jig 15 to rotate around its axis as generally known in the art. The second clamp jig 20 also has a circular hollow body as with the first clamp jig 15. The second clamp jig 20 is also mounted on a separate mounting base (not shown) opposite the first clamp jig 15 and is adapted to move toward and away from the first clamp jig 15. The first and the second clamp jigs 15, 20 adapted to securely clamp the glass disk between them. The second clamp jig 20 moves down toward the first clamp jig 15 in order to clamp the glass disk between the first and the second clamp jigs 15, 20. The face or clamp face 25 of the first clamp jig 15 includes a plurality of through holes 32 which will interact with a negative force such as a vacuum creating a vacuum seal sufficiently strong, capable of securing the glass disk onto the first clamp jig 15 or between the first and the second clamp jigs 15, 20 and able to hold the glass disk in place while chamfering is in progress. The clamp face 32 may further includes at least one groove 30 which will also interact with the vacuum to further enhance securing of the glass disk to the first clamp jig 15. The second clamp jig 20 moves away when each chamfering cycle is completed releasing the glass disk from the clamping so that the chamfered glass disk can be transported out of the clamp face 25 of the first clamp jig 15. A cylindrical grindstone 35 assembled to a retractable (or capable of moving up or down) and rotatable shaft 40. The second clamp jig 20 able to house the cylindrical stone 35. The said shaft 40 communicates to a driving unit (not shown) and by controlling the said driving unit, the shaft 40 rotates and in turn driving the cylindrical grindstone 35 to rotate around its axis. Preferably, the cylindrical grindstone 35 rotates in an opposite direction of a rotation of the first clamp jig 15. As mentioned, the cylindrical grindstone 35 is coupled to the retractable and rotatable shaft 40. Thus, the cylindrical grindstone 35 is operable control to extend, reaching the inside of the circular hollow of the first and the second clamp jigs 15, 20 through the circular center of the glass disk clamped between them enabling the cylindrical grindstone 35 to come into contact with the inner edge of the glass disk and chip away the rough edge of the glass disk. As mentioned, the apparatus 10 also includes a grindstone 45. The grindstone 45 adapted to rotate around it axis as well as adapted to move toward or away from the clamp jigs (15, 20) by a control unit as generally known in the art. The grindstone 45 also able to rotates in a direction opposite to the direction of rotation of the glass disk and adapted to grind the outer edges of the glass disk. The grinding of the outer edge of the glass disk by the grindstone 45 occurs simultaneously with the grinding of the inner edges of the glass disk by the cylindrical grindstone 35. Thereby, the peripheral inner and outer edges of the glass disk are being chamfered at the same time. Also as shown in Figs. 1, 2, and Fig. 4, the apparatus 10 comprising a cleaning means 50 to clean the face 25 of the clamp jigs 15, 20, either before commencing of chamfering or at the end of each chamfering cycle of each glass disk. The cleaning means 50 projected to the face 25 of the first clamp jig 15, and/or the first and the second clamp jigs 15, 20. The said cleaning means 50 realized as at least one pressurized fluid conduits 55 directing pressurized fluids to the face 25 of the first or second clamp jigs 15, 20 removing contaminants, such as glass chips, from the clamp jigs 15, 20. As shown in Figs. 1 and 2, for the embodiment with a single clam jig only one pressurized fluid conduit 55 is sufficient, whereas in the second embodiment with two clamp jigs as shown in Fig. 3, two pressurized air conduit is preferred in order to thoroughly and efficiently clean the face of both clamp jigs 15, 20. However, it is also possible to utilize only one pressurized fluid conduit with the second embodiment provided the pressurized fluid conduit is adapted to direct pressurized fluid toward both the first and the second clamp jigs 15, 20 either simultaneously or sequentially.

As shown in Fig.3, the pressurized fluid may be directed to the clamp jig's face 25 via two air conduits 55. Each air conduit 55 having one end communicates to a pressurized fluid source (not shown) and another end projected to the face 25 of the clamp jig 15, 20. One conduit 55 directs pressurized fluid to the face 25 of the first clamp jig 15 while another conduit 55 directs pressurized fluids to the second clamp jig 20. The conduits 55 or the pressurized fluid main is controllably operable by a valve communicates to the pressurized fluid source, whereby pressurized fluid may be released simultaneously or sequentially allowing a jet of pressurized fluid to sweep across the face 25 of the clamp jigs 15, 20. Preferably, the pressurized fluid is a pressurized air, readily available from the air-main of a robotic arm controlling unit, or from any other clean sources.

As mentioned, the apparatus also comprising a securing means for securing the glass substrate 12 to the clamp jig's face. The securing means may be realized as a vacuum force generating from a pump 16 placed beneath the first clamp jig 15. As described, the first clamp jig 15 includes a plurality of through holes 32 and /or may further include at least one groove 30 for aiding vacuum seal. The spaced-apart through holes 32 (from the bottom of the clamp jig's face 25) and the groove 30 distributed throughout circular body of the first clamp jig 15. Thus, as the glass substrate 12 is positioned onto the clamp face, the vacuum force through the through holes 32 causing a suction force capable of securely holding the glass substrate 12 onto the clamp face 25 while the chamfering is in progress. The securing means operate in same manner with the embodiment with the second clamp jig 20. The clamping of the second clamp jig 20 to the first clamp jig 15 further complement securing of the glass substrate 12.

Next, we will now describe the chamfering method according to the present invention as illustrated in Fig. 4. The main characteristic of chamfering method according to the present invention is that the method comprising a step of cleaning the face 25 of the clamp jigs 15, 20 either before commencing the chamfering cycle or at the end of each chamfering cycle and/or prior to the starting of the next chamfering cycle. In more detail, the chamfering method according to the invention comprising the following steps:

- Securing and positioning a glass disk onto the chamfering apparatus 10.

In this step, one glass substrate 12 having a disk shape with a center circular hole (glass disk) is positioned on to a chamfering apparatus 10, more specifically, on to the face 25 of a first clamp jig 15, by the assistant of a robotic arm (not shown) as generally known the art. The glass substrate 12 is secured thereto by securing means, for example, a vacuum generate by a pump 16 placed beneath the first clamp jig. The vacuum is applied (allowing the vacuum to come into contact with the glass substrate position on the clamp face through the through holes 32) to hold the glass disk on to the face 25 of the first clamp jig 15 prior to commencing chamfering. In the embodiment with the second clam jig 20, once the glass disk is in position, the second clamp jig 20 moves down to firmly clamp the glass disk between the first and the second clamp jigs 15, 20. The clamping of the second clamp jig 20 may be operated in parallel with the vacuum to complement securing of the glass substrate 12 by the vacuum or as stand alone. Other means of securing the glass substrate to the clamp jig are also possible.

- grinding the inner and outer peripheral edges of the glass disk to reach a predetermined smoothness value:

In this step, once the glass disk is firmly secured in position on the first clamp jig 15 or between the first and the second clamp jigs 15, 20, the cylindrical grindstone 35, such as a diamond wheel, which is coupled to the retractable and rotatable shaft 40 moves down toward the hollow body of the first clamp jig 15. The cylindrical grindstone 35moves down reaching the inside of the circular hollow body of the first clamp jig 15 or the first and the second clamp jigs 15, 20, as the case may be, through the circular center of the glass disk and adapted to grind the inner edge of the glass disk. The grindstone 45 also moves toward the glass disk and adapted to rotate and grind the outer peripheral edges of the glass disk being securely fixed on the first clamp jig 15 or between the first and second clamp jigs 15, 20, simultaneously to the grinding of the inner edge or independently (before or after grinding of inner edge) thereto. In an alternative method, while the glass disk is firmly secured the first and/or the first and the second clamp jigs 15, 20 rotate by the operation of clamp jig driving units. As a result, the glass disk also rotates. The cylindrical grindstone 35 also rotates by operation of its driving unit, but in an opposite direction of the rotation of the first and the second claim jigs 15, 20. The cylindrical grindstone 35 comes into contact with glass disk while rotates so as to grind away rough inner edge of the glass disk to reach a predetermined smoothness value. The outer peripheral edge of the glass disk is being grind simultaneously or sequentially with the grinding of the inner peripheral by the grindstone 45 which set to rotate in an opposite direction of the rotation of the glass disk. The abrasive quality of the grindstone chips away the rough outer and inner edges of the glass disk resulting is a smoother edges, thereby reducing cracks on the glass disk when subject to further treatments; removing chamfered glass disk from the first clamp jig 15 using the robotic arm as generally known in the art; and

- cleaning the clamp jigs 15, 20 by removing contaminant including glass chips from the face 25 of the clamp jigs 15, 20 prior to introducing the substrate onto the chamfering apparatus, more specifically, the clamp face or at the end of each chamfering cycle of each glass disk prior to introduction of the next glass disk on to the chamfering apparatus 10.

In this step, the faces 25 of the first and/or the first and the second clamp jigs 15, 20 of which came into contact with the glass disk during chamfering are cleaned in order to remove any contaminant including glass chips generated from the chamfering of a previous glass disk which may remain on the face 25 of the clamp jigs 15, 20. As the chamfering occurs in cycle and repeated for the next glass substrate, the step of cleaning may be performed before beginning of each chamfering cycle or at the end of each chamfering cycle, i.e. before introducing a glass substrate onto the clamp jig 15. The faces 25 of the fist clamp jig 15 and/or the first and the second claim jigs 15, 20, as the case may be, are cleaned by using a stream of pressurized fluid. Pressurized fluid is directed toward the face 25 of the clamp jigs 15, 20 and a jet of pressurized fluid is released to sweep across the face 25 of the clamp jigs 15, 20 blowing away contaminants including glass chips which may remain on the face 25 of the clamp jigs 15, 20. As the face 25 of the clamp jigs 15, 20 are wet due to uses of cooling agent during the chamfering process, the glass chips tend to stick to the face 25 of the clamp jigs 15, 20. Therefore, the pressurized fluid being used must be with sufficient pressured so as to blast the glass chips away from the clamp jig's faces 25. Although other kinds of pressurized fluids such as water may be used, it is less preferred as water tends to dilute the concentration of the cooling agent feed to the chamfering apparatus during chamfering. Thus, use of pressurized water could affect efficiency of the chamfering process. Accordingly, pressurized air, at the pressure of 3-5 bars is preferred. The pressurized air may be obtained from the existing air-main of the robotic arm control unit or from other separate clean air sources. Pressurized air may be released simultaneously from the conduits 55 or upper and lower grills 65, 70, allowing the air jet to sweep across the face 25 of the first and second clamp jigs 15, 20 simultaneously removing any glass chips remain on the faces 25 of the first and second clamp jigs 15, 20 at the end of each chamfering cycle. For optimum reduction in scratching, cleaning of clamp jig's face 25 should be carried out at each end of chamfering cycle of each glass disk and prior to introduction of the next and subsequent glass disk onto the chamfering apparatus.

By removing the glass chips from the faces 25 of the clamp jigs 15, 20, scratching cause by contamination of glass chips on the face 25 clamp jigs 15, 20 is eliminated or reduced. From a test conducted by the inventor, it was found that by employing the apparatus with a cleaning means and a step of cleaning the clamp jig in the chamfering process, the number of damage glass substrate or NG (no good) glass was reduced by 10% in comparison to the control sample without using the cleaning means or cleaning of the clamp jig during the chamfering process. Although this appears to be a small reduction, in large scale manufacturing environment, this figure represents large number of product. Hence the output or yield is improved.

In another aspect of the invention, the invention provides a method for manufacturing of a glass substrate. As shown in Fig. 5, the method comprising:

(1) Shaping and First Lapping Process

Plate-like glass members are obtained by any one of many known manufacturing methods using molten glass, such as a pressing method, a float method, a down-drawn method, a redrawing method, or a fusion method. It is recognized herein that the use of a pressing method can achieve the production of large quantities of glass substrates at low cost. The plate-like glass members may be any one of an amorphous glass, a ceramic or crystalline glass, an alumino-silicate glass, a soda-lime glass, a borosilicate glass, or the like. It is recognized herein that an alumino-silicate glass (Si02: 58 to 75 wt %; A1203: 5 to 23 wt %; Li20: 3 to 10 wt %; and Na20: 4 to 13 wt %) is preferably used for its capabilities of being chemically strengthened and having excellent flatness and strength. Thereafter, a lapping process was applied to both principal faces of each of the plate-like glass members so as to obtain disk-shaped glass base members. The lapping process was carried out using a double-sided lapping machine employing a planetary gear-type mechanism and using alumina-based free abrasive grains. Specifically, the lapping process was carried out by pressing lapping face plates onto both principal faces of each of the plate-like glass members from the upper and lower sides, supplying a grinding liquid containing said free abrasive grains onto the main faces of each of the plate-like glass members, and moving the plate-like glass members and the face plates relative to each other. By performing said lapping process, glass base members having flat principal faces were obtained.

(2) Cutting, Coring

Glass base members obtained from the above process were then cut using a diamond cutter to form disk-shaped glass substrates. Thereafter, a coring process was carried out wherein a concentric inner hole was formed for each of the disk-shaped glass substrates using a cylindrical diamond drill so as to obtain annular glass substrates.

(3) Second Lapping Process

A second lapping process was then performed to both principal faces of each of the glass substrates obtained from the above process in a similar manner to the first lapping process. In performing this second lapping process, fine irregularities on the principal faces of each of the glass substrates formed as a result of the above process are removable in advance.

(4) Chamfering Process

The glass substrate obtain from the process were then chamfered to smoothen the outer and inner peripheral edges of the glass substrate to reach a predetermined smoothness value in order to avoid cracking of the glass substrate when subject to further process down steam of the manufacturing line. The chamfering process according to the present invention is characterized in that it comprising a step of cleaning clamp jig face during which contaminant including glass chips were removed from the face of the clamp jigs prior to introducing the substrate onto the chamfering apparatus, more specifically, the clamp face or at the end of each chamfering cycle of each glass disk prior to introduction of the next glass disk on to the chamfering apparatus. (5) Edge Face Polishing Process

A brush polishing process was then applied to the outer edge face and the inner edge face of each of the glass substrates so as to achieve a mirror face state. In achieving a mirror face state, precipitation of sodium and potassium becomes prevented. In the said process, slurry of free abrasive grains containing cerium oxide abrasive grains was utilized as the polishing abrasive grains. Thereafter, the obtained glass substrates were thoroughly washed with water.

(6) First Polishing Process

A first polishing process was then carried out on the glass substrates obtained from the above process so as to remove cracks and/or strains remaining on the principal faces from the first and second lapping processes. In this first polishing process, the principal faces of each of the glass substrates were polished using a double-sided first polishing machine having a planetary gear-type mechanism and using upper and lower hard resin polishing pads. Cerium oxide abrasive grains used in the polishing liquid comprised a smaller diameter than the aperture diameter of the nap formation holes of the polishing pads.

The obtained glass substrates having been subjected to the said first polishing process were then cleaned by immersions in respective cleaning baths of neutral detergent, pure water and IP A (isopropyl alcohol).

(7) Second Polishing Process

A second polishing process was carried out so as to finish the principal faces to a mirror face state. In this process, the principal faces were mirror-polished using a double-sided second polishing machine having a planetary gear-type mechanism and using a softer resin foam polishing pad. Smaller diameter silica oxide abrasive grains than those of the first polishing process were used in the polishing liquid of the second polishing process. In this regard, the diameter of the said abrasive grains used in the second polishing process was smaller than the aperture diameter of the nap formation holes of the polishing pad.

Glass substrates having been subjected to the second polishing process were then cleaned by immersions in respective cleaning baths of neutral detergent, pure water, and IPA (isopropyl alcohol). An ultrasonic wave was applied to each cleaning bath.

(8) Chemical Strengthening Process A chemical strengthening process was then applied to the glass substrate by preparing a chemical strengthening solution in the form of a mixture of potassium nitrate (60%) and sodium nitrate (40%), heating this chemical strengthening solution to about 400C, preheating the cleaned glass substrate to about 300C, and immersing it in the chemical strengthening solution for about 3 hours. The immersion was carried out in a state where a plurality of glass substrates were placed in a holder so as to be held at their end faces, thereby enabling the entire faces of the glass substrate to be chemically strengthened.

In performing the immersion treatment in the chemical strengthening solution, lithium ions and sodium ions in a face layer of the glass substrate are replaced by sodium ions and potassium ions in the chemical strengthening solution, respectively, so that the glass substrate becomes strengthened. The thickness of a compressive stress layer formed at the face of the glass substrate was about 100 microns to 200 microns.

Glass substrates having been subjected to the chemical strengthening treatment were immersed in a water bath at about 20C so as to be rapidly cooled, and maintained for about 10 minutes. Thereafter, the rapidly cooled glass substrates were cleaned by immersing in concentrated sulfuric acid heated to about 40C. Thereafter, the glass substrates were immersed in respective cleaning baths of pure water and IPA (isopropyl alcohol) in turn.

In the past, glass chips on the chamfering jig cause scratching on the face of the glass substrate. Thus, high stock removal is a necessity in order to move such scratching (grinding deeper into the glass substrate beyond the depth of the scratch marks to achieve desired smoothness value of the glass substrate). High stock removal increases production cost in term of larger quantity of melted glass per piece of glass substrate, larger amount of polishing powder, longer time for lapping, polishing of which increase cost in term of man power (labor cost) as well. By taking early precaution in the chamfering process, i.e. by cleaning the clamp jig, scratching is less likely to occur. Therefore, it is no longer a necessity to remove as much stock as in the past. Thus, lowered production cost. In addition, as the current trend of technology requires a thicker glass disk, it is much easier to meet the product specification due to lower stock removal. Therefore, the chamfering method and apparatus according to the present invention as described clearly illustrate that objects of the invention as set out above have been met.