GB2132127A

GB2132127A - Hammer-tool attachment for portable hand-held electric drill

Info

Publication number: GB2132127A
Application number: GB08236097A
Authority: GB
Inventors: Frederick Jackson
Original assignee: Individual
Current assignee: Individual
Priority date: 1982-12-20
Filing date: 1982-12-20
Publication date: 1984-07-04
Also published as: GB2132127B

Abstract

A repetitive hammer blow attachment for use with hand held electric power drills, comprising of cylindrical housing 1 in which there is provided an axially reciprocating tool holder bolt 4, which is free to reciprocate but not rotate, and a rotary cylindrical hammer 9 which is free to reciprocate axially and rotate in one direction only. The tool holder bolt head 4 and the cylindrical hammer 9 are provided with aharp drop 14 mating axial cams 8, 11. The rotary cam is spring loaded against the reciprocating tool holder bolt 4 by a compression spring 27, and is rotated by an internal spine 10 of a rotating shaft 15 which is driven externally 21 by an electric power drill which results in repetitive hammer blows from the rotating reciprocating hammer 9 onto the tool bit holder. <IMAGE>

Description

SPECIFICATION Hammer tool attachment for portable hand-held electric drill The invention relates to a conversion tool attachment for use with a hand-held portable electric power drill. The attachment is capable of changing the rotary power of an electric drill into repetitive hammering blows with pure reciprocating motion.

To use a preferred embodiment of this invention, one only needs to unscrew the chunk from an electric drill and in its place screw in the attachment's spindle. The other end of the device is provided with a reciprocating tool holder into which can be fitted an assortment of tool bits with a variety of cutting shapes, cutting angles, rake angles and clearance angles, and made out of an assortment of hardened materials.

The drill thus converted is then capable of performing tasks such as chiselling, punching, hammering, making square holes as well as holes with sharp corners and also, when fitted with a bolster chisel, perform tasks like removing ceramic tiles from walls, and removing ceramic tile adhesive and plaster from walls.

Furthermore, such an attachment has the advantage of being small, compact, light and inexpensive and hence within easy affordable access for both the DIY enthusiast as well as the jobbing tradesman, neither of whom can afford the expense nor space required to possess existing purpose built hammer tools.

According to one preferred embodiment of the invention which is illustrated in the accompanying drawing, there is provided a hollow cylindrical housing 1 one end of which is provided with a long, square bore 2, and other end is open but provided with an internal thread 3.

Sliding inside the hollow square bore there is provided a tool bit holder bolt 4 which is square in cross section for most of its length, but provided with a cylindrical head 5. The tool bit holder bolt is free to reciprocate inside the square bore but is restrained from striking against the closed end 6 of the housing 1 by means of a strong (rebound) compression spring 7. The lower end of the hammer head 5 of the tool bit holder bolt 4 is formed in the shape of a plurality of axial cam teeth 8.

Also sliding in the cylindrical housing 1 there is provided a rotating cylindrical hammer 9. The rotating cylindrical hammer 9 is provided with a square bore 10 and, on the side facing the tool bit holder bolt 4, it is provided with a mating set of axial cam teeth 11. Each axial cam tooth 8 and 11 has a helical ramp 12, a crest 13 and a dwell 14. Preferably there is a sharp drop into the dwell 14 after a crest 13.

Inside the rotating cylindrical hammer 9 there is provided a rotary drive shaft 15. The rotary shaft 15 is provided with a solid axial cylindrical guide 16 at one end which slides and rotates inside an axial bore 17, provided in the head of the tool bit holder bolt 4.

The middle section 18 of the rotary shaft 15 is of solid square cross section and a sliding fit inside the square bore 10 ofthe rotating cylindrical hammer 9.

The lower end of the rotary shaft 15 is cylindrical in shape and is provided with a radial bearing (preferably radial ball bearing) 20. The extreme outer end 21 of the rotary shaft 15 is privided with a male thread 21 of a diameter size and form identical to the threaded spindle of the chuck of the electrical drill.

Preferably the spindle is also provided with a groove 23 into which there is fitted a circlip 24 to stop the shaft 15 from sliding further into the housing.

The radial bearing 20 is located inside a hollow cylindrical bearing housing/screw cap 25 which is provided with an external screw thread 22, which enables it to be screwed or unscrewed into or out of the internal thread 3 of the cylindrical housing 1. The lower end 26 of the screw cap 25 is provided with a bore which is large enough to be a clearance diameter for the rotating shaft 15 but too small to allow the circlip 24 to enter same.

Exerting an axial force between the rotating hammer 9 and the screw cap 25 there is provided a strong helical compression spring 27 and two spacing washers 28 and 29 on either axial side of same 27. Preferably the compression spring 27, although strong, is weaker than the rebound compression spring 7. The spacer washer 29, the external diameter of which fits inside the bearing bore of the screw cap 25, is preferably provided with a clearance recess 30 to allow freedom of movement of the radial ball bearing 20.

The lower end 26 of the screw cap 25 is provided with a square sectioned boss 26. The screw cap is constrained from accidentally unscrewing loose by the provision of a bent spring clip 31 and retaining screws 32, which is fitted in the screwed tapped hole 33 of the cylindrical housing 1.The bent spring clip 31 prevents accidental unscrewing of the screw cap 25 by engaging one of the flats of the square sectioned boss 26. The tool bit holder bolt 4 is preferably provided with a breather hole 34, and prior to assembly all the voids inside the cylindrical housing 1 are stuffed with a thick grease for lifelong lubrication The outer end 35 of the tool bit holder bolt 4 is hollow to permit is to accept a tool bit 36.The tool bits are preferably provided with a diametrical hole 37 and held in position by a retention screw 38, which screws into the diametrically tapped hole 39 provided in the end of the tool bit holder 4.

One side of the cylindrical housing 1 is preferably provided with a boss 40 and tapped hole 41 to permit the fitting of a screw-in handle grip 42 at right angles to the axis of the cylindrical housing 1.

As an optional extra, one side of the cylindrical housing 1 is provided with a tapped hole 43 into which is provided a screw 44 for retention of an adjustable slotted depth stopping strip.

Operation When the rotary shaft 15 is screwed into an electric drill (in place of the chuck) and the electric drill is switched on, the square section 18 of the rotary shaft 15 causes the rotary hammer 9 to rotate. However, due to the square shape of the tool holder bolt 4, rotation of the tool holder bolt 4 is constrained and consequently the axial cams 8 and 11 cause the tool holder bolt head 5 and cylindrical hammer 9 to be prized apart against the force of the two compression springs 27 and 7. The prizing apartwill continue until the profiles of the axial cam teeth 8 and 11 have reached their peak 13, after which the teeth fall abruptly into the dwell 14. Under the pressure of the compression spring 27 the cylindrical hammer 9 is now brought down hard with an impacting force upon the tool bit holder bolt 4, and if the tool bit 36 is resting on a workpiece, damage to that workpiece will result. In like manner, continued rotation of the spindle 15 will cause a series of repetitive blows from the rotating hammer 9 on the tool bit holder bolt4.

Claims

1. A repetitive hammer blow attachment for use with hand-held electric power drills, comprising of a cylindrical housing, in which there are provided a reciprocating tool holder bolt which is free to axially reciprocate but not rotate, and a rotating cylindrical hammer which is free to reciprocate and rotate in one direction only, both of which are provided with mating axial cams. The rotary hammer is pressed against the reciprocating tool holder bolt by a compression spring. The rotary hammer is provided with an internal axial spline, which is rotated by a mating splined rotary shaft, driven externally by an electric power drill

2. An invention as described in Claim 1, but where the end of the rotary shaft is provided with a screw thread identical to an electric drill chuck spindle screw thread.

3. An invention as in Claims 1 and 2, but where the internal spline of the rotating hammer and the section of the drive shaft that rotates it is of a square cross section.

4. An invention as in Claims 1,2 and 3, but where the tool holder bolt is constrained from rotary motion by virtue of its axial sliding element being rectangular (including square) in cross section.

5. An invention as in Claims 1,2,3 and 4, but where only one axial cam is provided in eitherthe tool holder head or the rotary hammer head, and the other element is provided with a hardened steel pin to act as an axial cam follower.

6. An invention as in Claim 5, but provided with an additional stronger helical spring spaced between the housing and the tool holder bolt head.

7. An invention as in Claim 6, but provided with a gripping handle at right angles to the cylindrical housing.

8. An invention as in Claim 7, but where the axial cam has a plurality of symetrical teeth about the centre of rotation and the profile of each tooth is so provided that there is a gradual rise to a peak, and a sharp drop into a dwell.