WO2014118771A1

WO2014118771A1 - Undercut tool

Info

Publication number: WO2014118771A1
Application number: PCT/IL2014/050084
Authority: WO
Inventors: Arieh Sher
Original assignee: Derio Medical Instruments Ltd.
Priority date: 2013-01-29
Filing date: 2014-01-23
Publication date: 2014-08-07

Abstract

A tool for forming undercuts in prefabricated boreholes includes a working head mounted on a driving shaft, both rotate at the same rotational speed. The working head center of gravity is always located eccentric to the driving shaft axis. As a result of the rotation of the driving shaft, centrifugal force is exerted on the working head causing it to slide outwardly relative to the driving shaft axis. The working head moves outwardly until its outer surfaces, which are impregnated with diamonds, come into contact with the borehole wall. With continued operation, the undercut tool grinds the borehole wall to create a widening of the borehole surface with a shape corresponding to the outer surface contour of the working head.

Description

Undercut tool

DESCRIPTION

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent Application Ser. No.

61/757,734, filed January 29, 2013, entitled "Undercut Tool", the entire disclosure of which is hereby expressly incorporated by reference herein.

FIELD OF THE INVENTION

The present invention relates generally to drilling devices, and, particularly, relates to undercut tools for providing increased anchorage, by creating an undercut in a prefabricated borehole.

BACKGROUND OF THE INVENTION

The need for anchoring objects to other surfaces is well known. The material of the substrate may be plastic, wood, bone, concrete, metal, for example, and thus requires any anchoring system that is acceptable to many materials. Some materials, such as concrete, are brittle and are not able to be threaded by a tap and thus the borehole must be otherwise modified to hold an anchoring system. Concrete anchoring system comprising anchor bolt that are glued into the borehole, or anchor bolts with expandable walls may, under stressful conditions such as high vibrations, lose their grip to the borehole wall which eventually results in failure of the anchoring system. A modification of the borehole by undercutting the wail of the borehole increases the force needed to pull out the anchor, thus providing a suitable solution to this problem.

The solution for forming undercuts in prefabricated boreholes is addressed in prior art. There are devices that use mechanical elements for operation, for example, US

6,213,859, US 8,122,978, US 7,188,690, etc.

Other devices, which are relevant to the present invention, exploit centrifugal force. For example, US 4,978,258 discloses a cutting tool that is made up of a tubular drive shaft and a cutting member combining to form a ball joint for the pivotal support of the cutting member. The drive shaft has an axially extending guidance bore with a pair of oppositely located guidance stop faces for guiding a shank section of the cutting member in a position eccentric to the axis of the drive shaft at the ball joint. As the drive shaft rotates, centrifugal force acts on the cutting member and causes the cutting head to contact the borehole wall. Such contact imparts a rolling motion to the cutting member around its own axis opposite to the rotation of the drive shaft in addition to the entrainment afforded by the rotating drive shaft, whereby the cutting elements in a repetitive and alternating manner contact the borehole wall and use the rotational energy imparted to the cutting member for effecting the material removal by striking or impact. Further, a scraping type of material removal is superimposed on the impact type, because of the entrainment rotary motion provided by the drive shaft.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a tool for forming undercuts or circumferentially extending widened sections in prefabricated boreholes. The tool permits the formation of undercuts of a definable shape and at a predetermined depth into a borehole.

In accordance with the present invention, the undercut tool is made up of a tubular drive shaft, a plug with a slot attached to the leading end of the driving shaft and a working head. The driving shaft is connected to the drill chuck by various known means. The drill, the means of connecting the shaft, and water recycling system are not detailed here as they are not parts of the present invention. The working head has an extension that protrudes into a slot in the plug, extending along the radius of the plug. It is to be noted that another feasible design is that the elongated slot is located in the working head whereas the plug has an extension.

This construction enables only a limited linear movement of the working head along the slot of the plug between two defined positions. One position defines the minimal eccentricity of the center of gravity of the working head to the axis of rotation (which is the driven shaft axis) and the second position defines the maximum eccentricity of the working head center of gravity to the axis of rotation. The working head is fastened to the plug with a sliding plate and a screw such that the only possible movement of the working head is limited to sliding along the slot of the plug.

After the insertion of the undercut tool into a prefabricated borehole, as the drive shaft starts to rotate, centrifugal force acts on the working head and causes it to slide in the slot, outwardly away from the drive shaft axis. Centrifugal force is developed due to a minimal eccentric displacement of the working head center of gravity from the rotation axis. This eccentricity becomes bigger as the working head slides outwardly relative to the driving shaft axis. The centrifugal force acts on the working head and causes it to come in contact with the borehole wall. All the surfaces of the working head that come in contact with the borehole wall are plated or impregnated with diamonds, CBN (Cubic Boron Nitride), tungsten carbide or other abrasive super hard particles of the desired grit size. With continued operation, the undercut tool creates a widening of the borehole surface with a shape corresponding to the outer surface contour of the working head. It is to be noted that the working head can be designed in various surface shapes e.g., sloped, straight, corrugated etc.

The undercut tool works optimally when it is driven by a high speed drill. An example of such a drill is Hilti DD EC-1 or Weka DK 1 1 Diamond coring tool. These drills rotate at no load at a speed of approximately, 9200RPM, and with load at approximately 6000RPM. Working at such high speeds results in significant centrifugal force as can be calculated from the formula below. Apart from this, the high speed enables using diamonds that actually grind the material rather than cutting it. Unlike cutting, grinding exerts small moments and forces and therefore the design of the undercut tool is simple. Although grinding with diamonds removes only small quantity of substrate material per revolution, compensation is achieved by the high rotation speed of the working head resulting in removal of a substantial amount of substrate material.

The centrifugal force is calculated by

Where:

F- Centrifugal force (Newton) m - Mass of working head (Kg)

E- Eccentricity of center of gravity of working head from axis of rotation (m) f- Frequency of rotation (revolutions/second).

Based on the above shown formula and the dimensions of the undercut tool, the contribution of changing the mass of the working head and the eccentricity to the centrifugal force is, relatively, small. The most significant parameter affecting the centrifugal force is the speed of rotation, as the centrifugal force is related to the square of the speed of rotation.

At the end of the operation the undercut tool must be pulled out of the borehole. To this end, the working head must be pushed towards the driving shaft axis. At the end of operation, the working head stays in contact with the undercut wail because there is no lateral force to push it towards the driving shaft axis. It should be noted that in case of the sloped working head there is no need for special means to push the working head towards the shaft axis. This is due to the fact that when the undercut tool is pulled out of the borehole, the sloped surface of the working head slides on the already created slope of the undercut, thus pushing the working head towards the drive shaft axis, in other cases, such as a straight working head, special biasing means e.g., coil spring are required to push the working head towards the shaft axis. Note: It is clear that the biasing means, although not absolutely needed, may be added to the sloped working head.

OBJECTS OF THE INVENTION

One object of the invention is to provide a tool for forming undercuts in prefabricated boreholes.

Another object of the invention is to provide an undercut tool that incorporates a working head that has various shapes for forming various undercuts.

Further object of the invention is to provide an undercut tool where the working head can be easily assembled and replaced.

Another object of the invention is to provide an undercut tool that has a compact and simple construction.

An additional object of the invention is to provide an undercut tool that can be operated by an existing drill without any additional provisions.

The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be made to the accompanying drawings and descriptive matter relating to the preferred embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. 1 is an isometric view of the undercut tool system.

FIG. 2 is an isometric view of the leading end of the undercut tool.

FIG. 3 is a longitudinal cross sectional view of the preferred embodiment of the undercut tool inserted in the borehole before starting its operation.

FIG. 4 is a cross-sectional view of the preferred embodiment along the line A-A.

FIG. 5 is a longitudinal cross sectional view of the preferred embodiment of the undercut tool at the end of its operation.

FIG. 6 is a cross sectional view of the preferred embodiment along the line B-B.

FIG. 7 is an isometric view of a second embodiment of the undercut tool.

FIG. 8 is a longitudinal cross sectional view of the second embodiment of the undercut tool at the end of its operation.

FIG. 9 is a longitudinal cross sectional view of the second embodiment of the undercut tool before pulling it out of the borehole.

FIG. 10 is an isometric view of a third embodiment of the working head.

FIG. 11 is a longitudinal cross sectional view of the third embodiment of the undercut tool at the end of its operation. DETAILED DESCRIPTION OF THE INVENTION

FIG. I shows the system of the undercut tool. It includes a drill 1 that rotates at high rotation speed. As an example, diamond coring tool Hilti DD EC-1 or Weka DK 1 1 , that are used for driving diamond bits, are suitable for driving the undercut tool. These drills include provisions for water recycling system, parts of it are shown: supply hose 3 collecting hose 2 and seal 4. Using water extends the lifespan of the undercut tool 5. The drill has a chuck for connecting the undercut tool 5 in the same way that diamond bits are connected to the drill. The drills and their provisions are not detailed here as they are not a part of the present invention.

FIG. 2 shows the leading end of the undercut tool 5. It comprises - a sloped working head 6, a plug 7, a sliding plate 8, a screw 9 and a driving shaft 10. The sloped working head 6 has an oval extension 11. All the surfaces 12 of working head 6 that come in contact with the wall of the borehole are impregnated with diamonds or CBN. Impregnation of the diamond can be done by known technologies such as vacuum brazing, electroplating or sintering. Oval extension 11 protrudes into oval slot 13 of plug 7 and is secured to it with sliding plate 8 and screw 9. Screw 9 is secured in the thread with thread locking adhesive such as Loctite. Alternatively, screw 9 may have a left hand thread opposing the right hand rotation direction of the drill. This construction enables working head 6 to slide radially along slot 13. In order to facilitate the sliding movement it is possible to harden and/or coat all the surfaces that come in contact with each other with a sliding material like PTFE. The surfaces that come in contact include: oval extension 11, slot 13 and sliding plate 8. Plug 7 is screwed to driving shaft 10. In order to prevent the loosening of plug 7, it is preferred that the thread of plug 7 is a left hand thread opposing the right hand rotation of the drive shaft 10. Plug 7 includes flats 30 to facilitate its assembly to driving shaft 10. It is clear that it is possible to weld plug 7 to driving shaft 10. The outside diameter of plug 7 is bigger than the outside diameter of driving shaft 10, but slightly less than the diameter of the prefabricated borehole. The surfaces 31 of plug 7 are hardened and/or coated with a sliding material like PTFE. A ring with the outside diameter of plug 7 can be attached to the driving shaft 10 at a distance from plug 9 in the direction of the drill 1 (not shown in drawing). This design, described in the preceding sentence, is aimed to limit the lateral movement of shaft 10 in the borehole during operation. Plug 7 also includes openings 14 that enable water to flow from driving shaft 10 to the diamonds on the working head 6.

FIG. 3 is a cross sectional view of the sloped undercut tool 5 inserted into the borehole, before driving shaft 10 starts to rotate. It is shown that the concrete 15 has a prefabricated borehole 16. The distance between the upper surface of the borehole 16 and the upper surface of working head 6 is arbitrary and is defined by the operator.

FIG. 4 is a cross sectional view along line A-A which shows a top view of the undercut tool 5. It is clearly shown that no part of working head 6 extends beyond the contour of plug 7, so it is possible to insert undercut tool 5 into the borehole 16. The center of gravity (C.G. in drawing) of working head 6 is located at a minimum eccentric distance (Emin) from the rotation axis. As a result of the undercut tool rotation, designated by arrow RPM, centrifugal force designated F is exerted on the working head 6 causing it to slide in the direction of F. Also shown, are two holes 14 located in plug 7 that enable water to flow from driving shaft 10 to the working head 6.

FIG. 5 is a cross sectional view of the sloped undercut tool 5 at the end of its operation. The undercut contour 17 in the concrete is an imprint of the contour of working head 6. It is possible to pull out the undercut tool 5 from borehole 17, because sloped surface 19 of working head 6 slides over the concrete undercut surface 17, pushing working head 6 towards the rotation axis.

FIG. 6 is a cross sectional view along line B-B which shows a top view of the undercut tool 5 at the end of its operation. The maximum eccentric distance (Emax) is determined by surface 20 of slot 13 (shown in FIG. 5). At this maximum eccentric distance the centrifugal force F reaches its maximum value.

FIG. 7 shows a second embodiment of the undercut tool 5. The working head 21 has straight surfaces. In this embodiment, the undercut tool cannot be pulled out of the borehole and therefore a biasing means is added, to force the working head 21 to move towards the rotation axis. The biasing means shown is a coil spring 23 located on guiding pin 24 that is threaded at its end. Plug 22 has a threaded hole 25 into which guiding pin 24 is screwed. Working head 21 has a bore 29 that accommodates spring 23. Other parts are the same as described in the first embodiment.

FIG. 8 shows the position of working head 21 at the end of its operation. In this case it is impossible to pull out undercut tool 5 because the lower surface of working tool 21 hits the substrate undercut 26. The role of the coil spring 23 is to push the working head 21 towards the rotation axis as shown in FIG. 9. The force of the coil spring 23 is smaller than the centrifugal force therefore it can be expressed only when there is no rotation of the drive shaft 10. When there is no rotation of drive shaft 10 it is possible to either insert undercut tool 5 into borehole 16 or to pull it out from borehole 16.

FIG. 10 and FIG. 1 1 show a third embodiment of the working head. The contact surfaces of working head 27 are corrugated so the imprint 28 in substrate 15 will also be corrugated. It is clear that other shapes of the working tool surfaces are possible.

While specific embodiments of the invention have been shown and described in detail to illustrate the application of the inventive principles, it will be understood that the invention may be embodied otherwise without departing from such principles.

Claims

CLAIMS What is claimed is:

1. An undercut tool for forming undercuts in prefabricated boreholes, said undercut tool comprises a driving shaft, a plug and a working head. Said plug contains an elongated slot that allows extension of said working head to slide outwardly relative to the driving shaft axis. Said working head rotates at the same speed of rotation with the driving shaft, and due to centrifugal force, slides on said plug outwardly until the outer surfaces of the working head come in contact with the borehole wall, said working head outer surfaces are impregnated with abrasive particles. With continued operation, the undercut tool creates a widening of the borehole surface with a shape corresponding to the outer surface contour of the working head.

2. Undercut tool, as set forth in claim 1, wherein said working head contains biasing means.

3. Undercut tool, as set forth in claim 1, wherein said elongated slot is located in the working head and wherein said plug has an extension.

4. Undercut tool, as set forth in claim 1, wherein said outer surfaces of the working head are sloped.

5. Undercut tool, as set forth in claim 1, wherein said outer surfaces of the working head are straight

6. Undercut tool, as set forth in claim 1, wherein said outer surfaces of the working head are corrugated.

7. Undercut tool, as set forth in claim 1, wherein said abrasive particles are diamonds.

8. Undercut tool, as set forth in claim 1, wherein said abrasive particles are CBN.

9. Undercut tool, as set forth in claim 1, wherein said plug is welded to said driving shaft.

10. Undercut tool, as set forth in claim 1, wherein said plug is screwed to said driving, shaft

1 1. Undercut tool, as set forth in claim 1, wherein said plug has water recycling openings.