FORM 2
THE PATENTS ACT, 1970 (39 of 1970)
COMPLETE SPECIFICATION
(Section 10)

■ MACHINE"
"A SPECIAL EXTENSION BOX FOR DEEP HOLE DRILLING"

LARSEN & TOUBRO LIMITED
L&T House,
Ballard Estate,
MUMBAI-400 00K Maharashtra state, India
An Indian Company registered under the
Provisions of the Companies Act 1956
The following specification describes the nature of this invention and the manner in which it is to be performed.

22 NOV 2004

The present invention relates to a special extension box for deep hole drilling machine. More particularly, it relates to an improved Guide Bush Assembly for deep hole drilling machine of drilling holes with large length-diameter ratio (Between 5 to 150).
It is also the object of the present invention to reduce the deflection of the drill tube and control the straightness of 19.3 mm diameter hole within close tolerance of 0.175mm in thickness of 426mm.
The object of the present invention is to extend the guide bush to reach out to surface, which is deep inside and drill a hole close to sidewall in the job.
Prior Art:
Deep Hole drilling is the machining of holes with a relatively large depth-diameter ratio. In normal drilling techniques depth is rarely more than five times the diameter. In deep hole drilling, the ratio may reach 150:1.
In prior art, there are three different techniques for deep hole drilling:
1. Gun Drilling.
This is for smaller diameters, in the range of .98 mm to 40.5 m. In Gun drilling the cutting fluid is supplied to the cutting edge through a duct inside the drill and chips are carried through a V-shaped flute along the outside of the drill.
2. Single Tube System (STS)
This is also known as BTA Drilling. This is suitable for diameters in range 15 to
130 mm.
Here the cutting fluid is supplied in the space between the drill tube and the
drilled hole. The cutting fluid then comes out along with chips through the drill
tube.
3. The Ejector System


This is used for diameters in range 18.4 to 130 mm. Here there is twin tube system where the cutting fluid is supplied in the space between inner and outer tube. The cutting fluid then comes out along with chips through the inner tube.
The function of the carbide bush assembly is to guide BTA drill head (which is a drilling tool) at the point of entry and to keep contact with surface of job and seal it so that cutting oil remains under pressure in the space between drill tube and wall of drilled hole.
Drawbacks in the prior art:
a) The carbide bush cannot reach the job surface, when a hole is to be drilled close to sidewall of the job. The Bush box obstructs with the side wall.
b) While drilling deep holes, the span of guides for BTA drill head and BTA drill tube assembly becomes excessive. This excessive span of guides causes the excessive deflection of BTA drill tube while drilling. In this situation, BTA drill head drifts away from the axis and affects the straightness of the hole.
It is the object of the present invention to rectify the drawbacks of prior art.
STATEMENT OF INVENTION
The present invention relates to a special extension box for deep hole drilling consisting of a main body (1) assembled in front of bush box which houses a carbide guide bush (5) to guide the drill head while drilling; a spieth bush (3) positioned concentric with the carbide guide bush (5), a clamping plate (4) to secure carbide guide bush (5) within the housing by four alien screws the improvement comprising an improved guide bush assembly having:
i) an improved guide bush (2) located behind the carbide guide bush (5); the
improved guide bush (2) having axial slots for passage of cutting oil and providing support to the drill tube (6) while it rotates and moves axially while drilling; and


ii) having an extension at front end with small external diameter so as to clear the side wall of the job, making it possible for front end of bush box to reach the surface of job which is deep inside.
DESCRIPTION OF THE INVENTION
The present invention is described with reference to the drawing. The figure shows the cross section of the bush box with special extended improved guide bush assembly in place. Key to the figure:
1- Main body
2- Improved guide bush
3- Spieth bush
4- Clamping plate
5- Carbide guide bush
6- Drill tube
7- Bush
According to the present invention, the special extension box for deep hole drilling consists of a main body (1) which is assembled in front of the bush box. It houses the carbide guide bush (5) through the spieth bush (3) and clamping plate (4).
The main feature of the present invention is the presence of improved guide bush assembly (2) positioned behind the carbide guide bush (5). This bush is made up of phosphor bronze and it guides the BTA drill tube precisely. It has axial slots which provide passage for cutting oil.
Advantages of the invention
• Since the external diameter of special guide bush extension is smaller and extended, it clears the sidewall if the job and makes it possible for front end of bush box to reach the surface of job which is deep inside.
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• In front of the bush box, the drill tube (6) is guided in the improved guide bush (2) just behind carbide bush where BTA drill head is guided.
• As the drilling progresses, BTA drill head looses the guide in carbide guide bush but the drill tube is constantly guided in the improved guide bush.
• At any point of drilling, BTA drill head and BTA drill tube assembly is guided in three points, i.e. at cutting point, the improved guide bush and in the bush (7) at the rear end of the pressure head.
• Due to three supports instead of two in the prior art, total span of guides gets reduced as compared to prior art.
• This reduced span reduces the deflection of BTA drill tube, thereby reduces the drifting of BTA drill head from the axis and improves the straightness of hole.



1. A special extension box for deep hole drilling consisting of a main body
(]) assembled in front of bush box which houses a carbide guide bush (5)
to guide the drill head while drilling; a spieth bush (3) positioned
concentric with the carbide guide bush (5), a clamping plate (4) to secure
carbide guide bush (5) within the housing by four alien screws the
improvement comprising an improved guide bush assembly having:
i) an improved guide bush (2) located behind said carbide guide bush
(5); said improved guide bush (2) having axial slots for passage of cutting oil and providing support to the drill tube (6) while it rotates and moves axially while drilling ; and
ii) having an extension at front end with small external diameter so as to clear the side wall of the job and make it possible for front end of bush box to reach the surface of job which is deep inside.
2. A special extension box for deep hole drilling as claimed in claim 1, wherein said improved guide bush (2) is made up of phosphor bronze.
3. A special extension box for deep hole drilling as claimed in claims 1 and 2 as described with reference to the drawing.
Dated this 20th day november 2004
M. D. BHATE AGENT FOR APPLICANT
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