WO2009066312A1

WO2009066312A1 - A polishing mill for polishing gemstones

Info

Publication number: WO2009066312A1
Application number: PCT/IN2008/000461
Authority: WO
Inventors: Janak Mistry
Original assignee: Janak Mistry
Priority date: 2007-07-17
Filing date: 2008-07-17
Publication date: 2009-05-28

Abstract

The present invention provides a polishing mill comprising a spindle having a scaife for polishing gemstones and a motor having a hollow shaft wherein said spindle passes through or in the said hollow shaft coaxially.

Description

TITLE

A POLISHING MILL FOR POLISHING GEMSTONES

FIELD OF THE INVENTION

The present invention relates to polishing mills for polishing gemstones, such as Diamonds.

DESCRIPTION OF THE BACKGROUND ART

Rough gemstones are processed in various multi-step, time and effort consuming techniques, such that precious and semi-precious polished gemstones and diamonds (hereinafter referred to as 'gemstones') are obtained. The processing steps are usually involved with measurable abrasion of the surface of a rough or semi-rough gemstone, by means of a rotating tool, such that the manufacturing is continued inwards from the outer surface of the rough stone to a predetermined position inside the stone, wherein the facets of the produced gemstone are lying. There have been various ways and methods used in the prior art and today, by which gemstones are polished according to the predetermined set values to meet the requirements of the industry. The stone to be cut or polished is held in a device known as a dop, which is adapted to run-in contact with the surface of the rotating wheel (also known as scaife and hereinafter referred to as scaife) to effect polishing of the stone. These polishing wheels are necessarily run at very high speeds to properly effect the cutting or polishing of the facet of the stone. Another necessity is that these polishing wheels must run perfectly in a horizontal plane without any tipping or wobbling to avoid uneven cutting or polishing of the stone. One of the commonly used polishing mills is shown in Fig 1. This polishing mill has a polishing wheel or Scaife (S) fixed to the spindle that rotates by means of a motor (E). A belt and pulley mechanism (C& D) is fixed to the spindle, the pulley forms part of the spindle, wherein the belt engages with the motor (E). Both the ends of the spindle are formed into two conical static points (A & B). Each conical point is supported under a static bearing material, to counter the axial movement of the rotating spindle.

But there is a problem with such kinds of polishing mills. Due to the radial force associated with the belt drive system, the spindle moves on motor side resulting an uneven wearing of static bearing material, causing dislocation of the spindle axis, particularly so at the lower end support. The lower end of spindle shifts toward the motor (E) causing a small tilt in the alignment of the spindle, that poses adverse effect on the rotational plane of the Scaife (S). Face of the Scaife (S) starts rotating in different planes to a deviational degree at different times and this deviationa! degree from the standard keeps changing thought the day during the operation of polishing mills.

This rotation of Scaife (S) in different planes is extremely critical for the quality of polishing as desirable to be achieved. As an attempt to tackle the problem of the Scaife rotating in different planes, a system of polishing benches is devised that has a spindle mounted with the motor, as referred in Figure 2. In this system the belt and pulley assembly of the previous polishing mills is completely eliminated and the rotating spindle (G) is directly engaged with the motor (E). Advantage offered by this new improved polishing system was that a defined plane of Scaife face (S) was achieved and the axis of the spindle rotation does not change. The problem that even this arrangement faces is that there will be a small amount of axial movements of the spindle axis, which is attributed to axial run out of the rolling bearings. This is due to the fact that the rolling contact bearings make use of spherical balls or cylindrical rollers, where the axis of rotation of these balls / cylinder and the assembly axis is not same. Due to manufacturing limitations, the size of these balls / cylinders and concentricity of the races is never controlled to zero tolerance. Due to these non-zero tolerance values, the rotational axis will never remain unaltered. In fact it will keep changing during the complete process of rotation along the assembly axis.

Theoretically, the axis of inner race and the outer race in a rolling contact bearing should be same, but practically is never same and keeps changing their relative position as the rolling contact balls / cylinders rotates between the races. This causes dynamic vibration, which has its adverse effect on the surface polish quality in gemstones.

This situation is of course objectionable and accordingly demands an improvement. SUMMARY OF THE INVENTION One of the objects of the present invention is to provide a polishing mill that obviates above discussed problem.

Another object of the present invention is to provide a polishing mill for polishing gemstones having a stable plane of scaife. The present invention provides a polishing mill for a gemstone, comprising: a scaife for polishing the gemstone; a motor having a hollow shaft rotating about a vertical axis; a spindle for mounting the scaife adapted rotatably between two static bearing supports wherein said spindle extends coaxially through or in the hollow shaft of the motor; and a coupling for coupling the shaft and spindle to transfer rotary motion of the hollow shaft to the scaife.

In one embodiment of the present invention, the hollow shaft houses one of the static bearing supports. Advantageously, the hollow shaft houses bottom static bearing support. Alternatively, the spindle can be passed coaxially through and through the hollow shaft and supported by the static bearing out of the hollow shaft.

According to another embodiment of the present invention, the scaife is mounted permanently on the spindle. Alternatively, the scaife is mounted removably on the spindle. A BRIEF DESCRIPTION OF THE DRAWINGS

Reference will be made to embodiments of the invention, examples of which may be illustrated in the accompanying figures. These figures are intended to be illustrative, not limiting. Although the invention is generally described in the context of these embodiments, it should be understood that it is not intended to limit the scope of the invention to these particular embodiments.

Figure 1 illustrates the cross-sectional view of a polishing mill as available in the prior art. Figure 2 illustrates the cross-sectional view of the polishing mill showing the integration of the rotating spindle with the motor according to the prior art. Figure 3 illustrates the cross-sectional view of the polishing mill according to an embodiment of the present invention. Figure 4 illustrates the cross-sectional view of the polishing mill according to another embodiment of the present invention.

A BRIEF DESCRIPTION OF THE INVENTION

In preferred general terms, the present invention provides a polishing mill comprising a spindle having a scaife for polishing gemstones and a motor having a hollow shaft wherein said spindle passes through or in the said hollow shaft coaxially.

Referring to Fig 3-4, embodiments and perspective view of a polishing mill (100) according to present invention are shown. The polishing mill (100) generally comprises a scaife (110) having a polishing surface (not shown) and a spindle (120) passes centrally through the scaife

(110), which is driven about a vertical axis (Y-Y). The scaife can be adapted permanently or removably on the spindle.

According to the present invention, the spindle (120) is adapted between two static bearings supports (150) namely top static bearings support (150A) and bottom static bearings support (150B) which helps to hold the spindle rotatably about the vertical axis helping to rotate the scaife in one and single plane.

Preferably, the spindle (120) has conical ends (120A, 120B) engaging with the conical recesses of the bearings (not shown) of the static bearings supports (150). The engagement of spindle with the static bearing support is not limited to conical arrangement and can be done by alternative available ways and is not required to discus in details as person skilled in the art can easily do and understand.

According to the present invention, as shown in Figures 3 and 4 the spindle (120) is passed through or in a hollow shaft (130) of motor (125) before adapting between the static bearings supports (150). According to the present invention, the spindle (120) is adapted in the hollow shaft (130) in such a way that the vertical axis of the spindle (120) is coaxial with a rotating axis (Y-Y) of the hollow shaft (130) of the motor (125).

The spindle (120) is coupled with the hollow shaft (130) of the motor (125) with the help of axial coupling (140) to transfer rotary motion of the hollow shaft (130) of the motor (125) directly to the scaife (110) through the spindle (120). Due to the axial coupling (140), there will be no radial load on the spindle (120) and thus there will be no tilt of rotating axis (Y-Y), thereby allowing the rotating plane of the scaife to be remained unaltered, that is, the scaife (110) rotates in one and single horizontal plane only. Advantageously, axial coupling (140) can be a flexible coupling for vibration damping or noise reduction. One embodiment of the present invention is shown in Fig 3 wherein the motor (125) is fixed in a way that the hollow shaft (130) of the motor (125) houses the bottom static bearing support (150B). In other word, the bottom static bearing support (150B) supports the spindle (120) in the hollow shaft (130) without any physical contact with the hollow shaft (130) and/or motor (125). In the another embodiment of the present invention as shown in Figure 4, the spindle (120) can be passed through and through the hollow shaft (130) coaxially and supported between the static bearings supports. Both the embodiments depend upon the vertical space available for polishing mill and length of the spindle.

The axial coupling between the shaft and spindle may be adapted below the table or above the table. Preferably, the axial coupling between the shaft and spindle is below the table. The other conventional parts (not shown) of the polishing mills such as dop, tang plates, dop support and other polishing accessories and inventions in those parts can be adapted as like in the conventional/available polishing mills. According to the present invention, the motor (125) is preferably fixed below the table (not shown) of the mill i.e. below the scaife matching the rotating axis with the rotating axis of the spindle. Preferably, the motor is fixedly adapted below the table on the ground to avoid transfer of vibrations of motor to the table. Alternatively, the motor may be fixedly adapted to the table. Alternatively, the motor can be fixedly adapted above the scaife. Advantageously, the hollow shaft may house the top bearing support.

As in the polishing mill of the present invention, the spindle securing the scaife is adapted between the two static bearing supports and the rotating axis of the motor and the scaife is one and the same, the scaife rotates in one and single horizontal plane without any tipping or wobbling thereby avoid uneven cutting or polishing of the stone resulting in the excellent surface finish of the gemstone with controlled faceting and control on facet angle also.

The principle of this invention is in the adapting a spindle carrying scaife rotatably between the two static bearing supports by allowing passing of the spindle coaxially through a hollow shaft of the motor to which said spindle is coupled with the hollow shaft and is, of course, to be understood that the present invention is, by no means, limited to the particulars shown in the drawings but also comprises any modifications within the scope of the appended claims.

Claims

CLAIMS:

1. A polishing mill for a gemstone, comprising: a scaife for polishing the gemstone; a motor having a hollow shaft rotating about a vertical axis; a spindle for mounting the scaife, said spindle adapted rotatably between two static bearing supports wherein said spindle extends coaxially through or in the hollow shaft of the motor; and a coupling for coupling the shaft and spindle to transfer rotary motion of the hollow shaft to the scaife.

2. A polishing mill as claimed in claim 1 , wherein the hollow shaft of the motor preferably houses one of the static bearing supports.

3. A polishing mill as claimed in claim 2, wherein the hollow shaft preferably houses bottom static bearing support.

4. A polishing mill as claimed in claim 1 and 3 wherein said coupling is preferably adapted below the table of the polishing mill.

5. A polishing mill as claimed in 1 or 2, wherein said coupling is flexible coupling.

6. A polishing mill as claimed in claim 1 , wherein said spindle has conical ends engaging with the conical recesses of the bearing of the stationary ends.

7. A polishing mill as claimed in claim 1 , wherein said scaife is permanently adapted on the spindle.

8. A polishing mill as claimed in claim 1 , wherein said scaife is adapted removably on the spindle.

9. A polishing mill substantially as herein described with reference to the foregoing description with the accompanying drawings.