GB2248200A - Expansible drill bit for undercutting bores - Google Patents

Abstract

The drill comprises a rotatable tubular drill body 10 having an axial bore, a first blade 12 at one end of said drill bit for cutting a bore, and at least one radially extending arm 14 attached by hinged means 16 at one end of the drill body such that the arm is pivotal radially outwards. Second cutting means 17 are formed in the arm and the arm is moved pivotally radially outwards by axial movement of a non-rotatable shaft 21 carrying a rotatable collar 23. <IMAGE>

Description

FURTHER IMPROVEMENTS IN DRILLS The invention relates to improvements in drills for undercutting holes.

Many building components such as walls, roofs etc. are required to support some form of fixing, such as a bolt or an anchor. Many such fixings are used nowadays which have an expanding sleeve or skirt, which, once the fixing is inserted into a bore in the building component, is then expanded. Expanding fixings are advantageous in that they provide an increase in the bearing strength of the fixing for a smaller contact area. Thus the fixing may be more securely fixed or a shorter fixing and shallower hole may be used.

The main disadvantage of such fixings lies in that there is only a small area of actual contact between the fixing and the walls of the bore in which it is affixed.

Some drills are now available which are capable of forming an undercut or cavity within the bore below the surface of the component. When a fixing is expanded in an undercut bore, there is a far greater area of contact between the fixing and the walls of the bore and it is far more secure.

Applicant's published patent application GB-A-2184962 describes an expansible drill for forming an undercut. The drill disclosed in this document comprises a cylinder having an incorporated cutting edge at one end. The end of the cylinder is slotted and can be expanded by tightening a nut on the end of the central shaft sticking out of the bore. This forces a frusto-conical wedge inside the slotted end of the cylinder causing it to expand radially.

The problem with this drill is that whilst it functions extremely well it is expensive to produce.

GB-B-2157207 also discloses an undercutting drill. Again in this drill the blades carrying the cutting teeth are flexible and are forced to expand radially as the body of the drill is forced over the conical guide. The latter is effected by pushing the drill against the bottom of the bore so that the guide, which is movable axially relative to the drill body, can move no further and the blades thus slide over the guide sides and consequently are expanded.

Alternatively, a collar is described which bears on the outer surface of the material having the bore.

The collar is fixed to the lower half of the drill body, whilst the upper half is movable relative thereto in an axial direction.

The retraction of this drill relies on the recovery of the blades which have been forced to expand. If this were not to happen, perhaps due to fatigue or excessive friction the drill would be useless. Additionally the bore would probably be wrecked whilst trying to extract the useless drill.

It has been found that the drill is also difficult to use because of the force required to expand the blades. The friction caused by the blades moving over the cruciform guide is quite substantial and prevents ease of use. Also the length of the drill required to ensure that the upper and lower parts of the drill body are movable relative to each other made the drill cumbersome and difficult to use.

The problems encountered with all these drills is that a separate drill is needed to cut the parallel sided bore before the undercutting drill can be used and this therefore makes the process of undercutting more time consuming and expensive.

Many of the existing drills cannot be used to drill the initial bore because their means for expanding to form the conical undercutting edge protrude from the end of the drills. Furthermore, most of the conical undercutting surfaces are shaped so that it would not be possible to extract the dust resulting from the bore being cut, which would result in cutting difficulties and inefficiency.

It is an object of the present invention to provide an improved drill for forming a bore and undercutting it.

According to the present invention there is provided an expansible drill bit for drilling and undercutting bores comprising a rotatable tubular drill body having an axial bore, first cutting means at one end of said drill bit for cutting a bore, at least one radially extending arms attached by hinge means at one end of the drill body such that the arm is pivotal radially outwards, second cutting means formed in the arm, means for pivotally moving the arms radially outward so as to undercut the bore drilled by the first cutting means.

A preferred embodiment of the present invention will now be described by way of example only, with reference to the accompanying drawings in which: Fig. 1 is a side elevation of a portion of a drill according to the invention, and Fig. 2 is a section on line II-II of Fig. 1.

The drill bit 10 comprises a rotable generally tubular body 11 which is attached either directly or through a gear box to driving means (not shown). One way in which this can be done is described in applicant's co-pending application No. 9015577.1.

The body 11 is made from steel or any other suitable material and at an end opposite the end connected to the driving means has first cutting means 12. The first cutting means 12 can be of any suitable shape which would enable a parallel walled bore to be drilled when the drill 10 is rotated and pressure applied against a building component.

Second cutting means 13 are also provided. The second cutting means comprise a pair of pivotal arms 14 positioned within slots 15 cut axially in the body 11. The arms 14 are hinged to the drill body 11 by a hinge of any suitable means. In Figs. 1 and 2 the hinge is shown as a pin 16 located within a co-axial hole drilled through each arm 15 and the body 11. The hinge allows one end of the arm 14 to swing our radially in an arc. In the outer surface of each arm 14 are formed cutting teeth 17 and the arms 14 are substantially the same length as the slots 15. In the embodiment of the invention illustrated there are two arms 14 used, although the invention is not limited to this number. In the inner surface of each arm 14 is curved to form a projection 18 at the end furthest from the hinge.

A circlip 20 or other suitable means is used to prevent the arms 14 from swinging out of the slots 15 of their own accord. The circlip 20 generally restrains the arms 14 so that the projection 18 lies within the bore of the tubular body 11. The circlip 20 must be of a suitable design to allow the arms 14 to be extended when a suitable force is applied, but which easily recovers its original position when the force is removed to cause the arms 14 to retract again as shown in Fig. 2. The circlip 20 preferably lies within a groove in the outer surface of the tubular body 11.

The force to extend the arms 14 is applied by means of a non-rotating shaft 21 which is axially slidable within the tubular body 11. Movement can be effected by means of a trigger as described in applicant's co-pending application No. 9015577.1, or any other suitable manner.

Located on a spigot 22 on the end of the non-rotating shaft 21 is a rotable collar 23 held in position by a circlip 24. When the drill is in use and the tubular body 11 is rotating relative to the shaft 21, the collar 23 which is in contact with the inner surfaces of the arms 14 will also rotate thus avoiding friction between the tubular body 11 and the shaft 21. The projections 18 on the inner surfaces of the arms 14 are shaped such that as the collar 23 travels towards the end of the rotating tube 11 it forces the projections 18 outwards such that the arms 14 swing outwards. It should be noted that although this is one way of extending the arms, the invention is not limited to this method and any other suitable method can be employed.

To enable the drill 10 to operate effectively it is necessary to remove the dust formed during the cutting of the initial bore. The tubular body 11 therefore has a pair of helical grooves 30 cut into its surface to assist the flow of dust.

It should be noted that the grooves need not be helical, and may vary in number and shape. For example, if the drill has three pivotal arms one or more grooves may run parallel to and between them before becoming helical. Alternatively a helical groove may have a very large pitch at the end of the drill where the pivotal arms are located to avoid the arms and a smaller pitch over the rest of the length of the drill. The depth and width of the groove may also vary along the length of the drill bit.

In use, the drill bit 10 is connected to power driving means and placed against the building component in which the hole is desired. As the drill bit 10 is rotated and pushed against the building component the first cutting means 12 cuts a parallel sided bore in the component, the dust from which is transported externally of the bore by means of the grooves 30. When the desired depth is reached, axial pressure on the end of the drill is released and the shaft 21 moved towards the cutting end of the drill bit to cause the arms 14 to expand outwards whilst the drill bit is still being rotated. As the collar 23 travels along in contact with the inner surfaces of the arms 14, it forces the arms 14 outwards thereby expanding the drill bit 10 to cut a conical shaped undercut.

When the drill bit 10 is to be withdrawn from the bore, the non-rotating shaft 21 is retracted away from the arms 14. The circlip 24 then is allowed to recover causing the arms 14 to move inwards to their original position. The drill 10 may then be withdrawn.

Claims (12)

CLAIMS:

1. An expansible drill bit for drilling and undercutting bores comprising a rotatable tubular drill body having an axial bore, first cutting means at one end of said drill bit for cutting a bore, at least one radially extending arms attached by hinge means at one end of the drill body such that the arm is pivotal radially outwards, second cutting means formed in the arm, means for pivotally moving the arms radially outward so as to undercut the bore drilled by the first cutting means.

2. An expansible drill bit as claimed in claim 1 in which there are provided means to remove dust resulting from the drilling of the bore, from the bore.

3. An expansible drill bit as claimed in claim 2 in which the dust removing means comprise at least one groove in the outer surface of the tubular drill body.

4. An expansible drill bit as claimed in claim 3 in which the groove is helical.

5. An expansible drill bit as claimed in claim 4 in which the pitch of the groove is regular.

6. An expansible drill bit as claimed in claim 4 in which the pitch of the groove is irregular.

7. An expansible drill bit as claimed in any one of claims 3 to 6 in which only a portion of the groove is helical.

8. An expansible drill bit as claimed in any one of claims 3 to 7 in which the depth and/or width of the groove vary along the length of the drill bit.

9. An expansible drill bit as claimed in any one of the preceding claims in which there are a plurality of arms disposed within slots cut axially in an end of the drill body.

10. An expansible drill bit substantially as hereinbefore described with reference to and as shown in the accompanying drawings.

11. An expansible drill comprising a drill bit as claimed in any one of the preceding claims and means for driving said drill bit.

12. A method of drilling and undercutting bores using the drill as claimed in claim 10 comprising the steps of; a) driving the drill bit to rotate whilst the drill bit is in contact with a building component in which the hole is to be formed, the radially extending arms of the drill body being held in a retracted position within said slots to thus cut the bore to the required depth; and b) causing the radially extending arms to pivot outwards to undercut the bore.