FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
As amended by the Patents (Amendment) Act, 2005
AND
The Patents Rules, 2003
As amended by the Patents (Amendment) Rules, 2005
COMPLETE SPECIFICATION
(See section 10 and rule 13)
TITLE OF THE INVENTION
An improved countersunk locking mechanism.
APPLICANT(S)
Crompton Greaves Limited, CG House, Dr Annie Besant Road, Worli, Mumbai 400 030, Maharashtra, India, an Indian Company
INVENTOR(S)
Sathe Mahesh Kashinath of Crompton Greaves Ltd, Speciality Products Cell, Industrial Design Centre, Global R&D, Crompton Greaves, Kanjurmarg (East), Mumbai- 400042 Maharashtra, India; an Indian National
PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the nature of this invention and the manner in which it is to be performed:

FIELD OF THE INVENTION
This invention relates to the field of mechanical engineering.
Particularly, this invention relates to countersunk screws and its fixtures.
Specifically, this invention relates to an improved countersunk locking mechanism.
BACKGROUND OF THE INVENTION
Mechanical parts need to be assembled using fixation devices such as screws. There are varied designs for such screws. Screws may be through through-holes wherein a through-hole is drilled through two abutting or adjacent mechanical parts and a screw is placed through the through hole. The stem of the screw resides in the hole while the head of the screw rests over the hole. The head may be a flat head or a bulbous head, and in such cases, projects over and above the general plane of the mechanical part surface. While it is okay to have a projecting head in many cases of mechanical abutment, there are certain cases which necessitate that the head be resident in line or within the plane of the mechanical part which is to be abutted. This may be for functional and / or for aesthetic value. In such cases, a countersunk hole is drilled which receives a countersunk screw. The countersunk hole and the countersunk screw form a countersunk locking mechanism.
A countersink is a substantially conical hole cut into a manufactured object or a mechanical part. A common usage is to allow the head of a countersunk bolt or screw, when placed in the hole, to sit flush with or below the surface of the surrounding material. A countersink may also be used to remove the burr left from

a drilling or tapping operation thereby improving the finish of the product and removing any hazardous sharp edges.
An enclosure design carrying countersunk holes with embosses on component requires to carry screw head, but the mating component carries flat wall for mating with screw head carrying mating component. This was just taking care of screw seating flush with screw head carrying component external face. Spring action generated through emboss wall was missed out since the emboss size was selected such that after drilling counter sunk screw head size hole into emboss, the emboss wall thickness is not reduced.
Therefore, there is a need for a better countersunk locking mechanism.
OBJECTS OF THE INVENTION
An object of the invention is to provide a countersunk screw locking without spring washer.
Another object of the invention is to provide a joint with a countersunk locking mechanism used in joints which can be used as standard feature on all sheet metal component assemblies and can improve product aesthetics and ergonomics.
Yet another object of the invention is to provide spring action based locking of countersunk screw and avoiding loosening of the countersunk screw due to vibration.
Still another object of the invention is to provide a countersunk locking mechanism such that mating component alignment is quick and correct.

An additional object of the invention is to provide a countersunk locking mechanism which ensures flush screw head seating with mating component external face.
Yet an additional object of the invention is to provide a countersunk locking mechanism which avoids breaking and loosening, thereby delivering a leak-tight joint.
SUMMARY OF THE INVENTION
According to this invention, there is provided an improved countersunk locking mechanism adapted to provide abutment between an operative outer surface and an operative inner surface, said operative inner surface comprises a stepped cut which is co-axial with a countersunk bore with a nut fitted in said stepped cut region in order to receive a countersunk screw, said mechanism comprising a countersunk hole on said operative outer surface, said countersunk hole with an annular sloping surface which is a circumcircle to a through hole, said conical surface being a relatively longer conical surface adapted to extend support to at least a portion more than half of a tapering / conical head of a countersunk screw adapted to sit in said mechanism, thereby providing a longer support base for said countersunk screw.
Typically, said countersunk hole is a conical indentation with a through hole.
Typically, the distance between inner diameter of said conical surface and outer diameter of said conical surface is relatively long.

Typically, said nut is a cleat / rivetted nut fitted in the stepped cut region in order to receive said countersunk screw which abuts said operative outer surface to said operative inner surface.
Typically, said annular sloping surface is of a pre-defined thickness such that it provides a resilient counter support to said countersunk screw with a conical mating surface which rests on said annular sloping surface.
Preferably, said annular sloping surface is of a pre-defined thickness such that it provides a resilient counter support to said countersunk screw with a conical mating surface which rests on said annular sloping surface such that head of said screw rests in the conical part of said bore, while the stem of said screw mates with the inner side of a nut provided in said stepped cut region.
Additionally, said mechanism comprising an O-ring fitted on the counterside of said annular sloping surface in order to deliver a leak-tight joint.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 illustrates a cut-section side view of an enclosure wherein a countersunk locking mechanism of the prior art is engaged; and
Figure 2 illustrates a zoomed view of the encircled portion of Figure 1.
The invention will now be described in relation to the accompanying drawings, in which:

Figure 3 illustrates a cut-section side view of an enclosure wherein a countersunk locking mechanism of the invention is engaged;
Figure 4 illustrates a zoomed view of the encircled portion of Figure 3;
Figure 5 illustrates a close-up isometric view of Figure 4; and
Figure 6 illustrates a nut adapted to be used with the improved countersunk locking mechanism.
DETAILED DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 illustrates a cut-section side view of an enclosure wherein a countersunk locking mechanism of the prior art is engaged.
Figure 2 illustrates a zoomed view of the encircled portion of Figure 1.
An enclosure outer cover (12) and an enclosure inner cover (14) are to be abutted and for the head of the screw to be flush with the enclosure outer cover surface, a countersunk locking mechanism is used. A countersunk bore (16) is made which penetrates through the enclosure outer cover (12). A stepped cut (22) is made in the enclosure inner cover (14). The stepped cut (22) is co-axial with the countersunck bore (16). A nut, typically a cleat / rivetted nut, (18) is fitted in the stepped cut region in order to receive a screw (24) which abuts the enclosure outer cover (12) to the enclosure inner cover (14). The cleat / riveted nut is typically press fitted in the stepped cut (22) region so that it sits across the steps of the stepped cur region in a firm manner. The countersunk bore (16) includes a conical surface (26) which

receives the conical complementary surface of the countersunk screw (24). As seen from Figure 2 of the accompanying drawings, a gap (28) is formed. This gap does not provide adequate gripping or locking of the countersunk screw (24) in the bore. There is a need for force distribution without the use of a washer or spring.
According to this invention, there is provided an improved countersunk locking mechanism.
Figure 3 illustrates a cut-section side view of an enclosure wherein a countersunk locking mechanism of the invention is engaged.
Figure 4 illustrates a zoomed view of the encircled portion of Figure 3.
Figure 5 illustrates a close-up isometric view of Figure 4.
Figure 6 illustrates a nut adapted to be used with the improved countersunk locking mechanism of this invention.
In accordance with an embodiment of this invention, there is provided a countersunk hole (52) on an operative outer surface (12). The countersunk hole is a conical indentation with a through hole. There is an annular sloping surface (54) which is a circumcircle to the through hole. The conical surface, according to this invention, is a relatively longer conical surface, as compared to the prior art, i.e. the distance between the inner diameter of the conical surface and the outer diameter of the conical surface is relatively long. This provides a longer support base from a countersunk screw (24) which sits in the countersunk hole and through hole.

The operative inner surface (14) includes a stepped stepped cut (22) (same as the prior art) which is co-axial with the countersunck bore (16). A nut, typically a cleat / rivetted nut, (18) is fitted in the stepped cut region in order to receive a screw (24) which abuts the enclosure outer cover (12) to the enclosure inner cover (14). The cleat / riveted nut is typically press fitted in the stepped cut (22) region so that it sits across the steps of the stepped cur region in a firm manner.
In accordance with another embodiment of this invention, the annular sloping surface (54) is of a pre-defined thickness such that it provides a resilient counter support to a countersunk screw (24) with a conical mating surface (55) which rests on the annular sloping surface. The head of the screw rests in the conical part of the bore, while the stem of the screw mates with the inner side of the nut (18). This annular sloping surface (54) of a pre-defined thickness is a thin emboss wall.
The inventive step of this invention lies in provisioning an improved spring-less and washer-less countersunk locking mechanism for having enclosure assembly screws seating flush or bit inside of enclosure component on screw head side externa] face, by allowing over travel of screw and at the same time spring action generated by the thin emboss wall on external component over pressing, locking screw unwinding due to vibration. In the prior art, countersunk screws do not carry spring washers or plain washers and loosening prevention was through friction force between mating countersunk head screw taper face and corresponding hole taper face holding the screw in place. This sometimes prevented over travel which may be required for screw head flush seating with mating component external face. This joint can be used as standard feature on all sheet metal component assemblies and can improve product aesthetics and ergonomics.

In accordance with another embodiment of this invention, an O-ring can be fitted on the counterside of the thin emboss wall in order to deliver a leak-tight joint.
While this detailed description has disclosed certain specific embodiments of the present invention for illustrative purposes, various modifications will be apparent to those skilled in the art which do not constitute departures from the spirit and scope of the invention as defined in the following claims, and it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the invention and not as a limitation.

We claim,
1. An improved countersunk locking mechanism adapted to provide abutment between an operative outer surface and an operative inner surface, said operative inner surface comprising a stepped cut which is co-axial with a countersunk bore with a nut fitted in said stepped cut region in order to receive a countersunk screw, said mechanism comprising a countersunk hole on said operative outer surface, said countersunk hole with an annular sloping surface which is a circumcircle to a through hole, said conical surface being a relatively longer conical surface adapted to extend support to at least a portion more than half of a tapering / conical head of a countersunk screw adapted to sit in said mechanism, thereby providing a longer support base for said countersunk screw.
2. A mechanism as claimed in claim 1, wherein said countersunk hole is a conical indentation with a through hole.
3. A mechanism as claimed in claim 1, wherein the distance between inner diameter of said conical surface and outer diameter of said conical surface is relatively long.
4. A mechanism as claimed in claim 1, wherein said nut is a cleat / rivetted nut fitted in the stepped cut region in order to receive said countersunk screw which abuts said operative outer surface to said operative inner surface.
5. A mechanism as claimed in claim 1, wherein said annular sloping surface is of a pre-defined thickness such that it provides a resilient counter support to

said countersunk screw with a conical mating surface which rests on said annular sloping surface.
6. A mechanism as claimed in claim 1, wherein said annular sloping surface is of a pre-defined thickness such that it provides a resilient counter support to said countersunk screw with a conical mating surface which rests on said annular sloping surface such that head of said screw rests in the conical part of said bore, while the stem of said screw mates with the inner side of a nut provided in said stepped cut region.
7. A mechanism as claimed in claim 1, wherein said mechanism comprising an O-ring fitted on the counterside of said annular sloping surface in order to deliver a leak-tight joint.