GB2114925A

GB2114925A - Work-head and a power device including such a work-head

Info

Publication number: GB2114925A
Application number: GB08205074A
Authority: GB
Inventors: George John Antoni Karwacki
Original assignee: Individual
Current assignee: Individual
Priority date: 1982-02-20
Filing date: 1982-02-20
Publication date: 1983-09-01

Abstract

A power drill has a rotary attachment sanding or polishing work- head 2. The work-head 2 has a Compressible resilient foam base 3 and the upper face 3a of the base 3 is secured by adhesive to a first generally disc-shaped rigid plastics carrier part 4 of the work-head. A thin sheet of flexible backing material 5 is secured by adhesive 5 to face 3b of base 3, and the backing material 5 receives a self-adhesive, removable abrasive sheet 6. The base has such compressibility and density characteristics that it is able to deform locally during a sanding or polishing operation to allow pressure to be spread over relieved or contoured areas of a workpiece and facilitate carrying out the operation. The drill is connected to the work-head by way of centrally located internally threaded sleeve 4b. <IMAGE>

Description

SPECIFICATION Work-head and a power device including such a work-head This invention relates to a work-head, for example, for use in sanding or polishing and to a power driven device including such a work-head.

The work-head may be an attachment to a power take-off of the device or be an integral part of the device.

Power driven work-heads of the rotary pr reciprocating type, including a hard rubber base to which separate abrasive sanding sheets may be attached, are well known. Rotary work-heads including a hard foam base with a backing to which self-adhesive abrasive sheets may be attached are also known. Problems which occur with work-heads of these types are that in carrying out a work operation such as sanding a relieved or contoured workpiece, especially a workpiece having deeply re-entrant or concave surface portions, the operation is made more difficult since a lot of care and attention may be required to perform the work operation without damaging the workpiece. Even where the workpiece is not contoured similar problems may arise. The hardness of the base, particularly around the periphery may cause damage to the workpiece despite some inherent resilience in the base.In a particular case of sanding-down operations on vehicle bodies with a rotary sanding work-head, areas of the vehicle body such as around the wheel arches or other relieved areas require particular care since normal hand pressure on the base may inadvertently cause damage to the vehicle body by cutting through the paint into the body instead of merely sanding the surface of the paintwork. When sanding-down such areas it can prove very awkward to achieve successful results with such a work-head, particularly for the nonexpert.

It is an object of the present invention to provide an improved work-head in which at least some of the aforementioned disadvantages are alleviated.

According to the present invention there is provided a work-head comprising a base secured to a first, carrier, part of the work-head and a sheet of flexible backing material secured by adhesive to a planar work-face of the base, the backing material being suitable for attaching a selfadhesive abrasive sheet thereto and capable of flexing with part of an abrasive sheet secured thereto and with part of the work-face out of the general plane of the work-face, the material and dimensions of the base being selected to suit parameters of a work operation or work operations to be performed by the work-head, for example, speed of movement of the work-head and pressure application to the work-head while performing a work operation, the material of the base being soft, compressible and resilient so that:: a) the base is capable of being locally deformed substantially over the entire area of the base including at the edge or edges of the base; b) in use of the work-head with an abrasive sheet in performing a work operation, the base is capable of being deformed locally so that the abrasive sheet flexes with part of the backing material and part of the work-face moves out of the general plane of the work-face allowing the base to conform substantially to the shape of a work-piece being operated upon by the workhead, c) the base does not collapse during the workoperation, thereby allowing the abrasive sheet to crease or tear but is resilient enough to sustain the abrasive sheet in worl < ing operation with the work-piece.

Further according to the present invention there is provided a power driven device including a work-head as described in the immediately preceding paragraph.

Still further according to the present invention there is provided a method of sanding, smoothing or polishing a workpiece, said method comprising: a) bringing a work-head having a base and a sheet of sanding, smoothing or polishing material secured thereto into working operation on a workpiece, said sheet being attached to a planar work-face of the base; b) moving said work-head relative to said workpiece with said sheet in contact with the workpiece;; c) applying pressure on said work-head in a direction generally towards the workpiece during said relative movement, to resiliently locally deform the base so that part of the work-face moves out of the general plane of the work-face with a part of said sheet, said local deformation being adjacent a raised or relieved portion of the workpiece such that the base conforms substantially to said raised or relieved portion of the base thereby spreading the pressure applied to said raised or relieved portion and facilitating sanding, smoothing or polishing said raised or relieved portion.

The first part of the worl < -head is, preferably, rigid and, in use, the first part is movable under pressure towards the backing material thereby resiliently compressing the base allowing the first part to tilt or float relative to the backing material.

when performing a work operation on a generally flat surface of a workpiece.

Preferably, the base is a foam material which in most cases will, preferably, be of open-cellular form since closed cell foams usually have a poorer compression 'set' and can therefore permanently distort under load. The foam material is, preferably, a polyurethane foam and may be a polyether or polyester foam.

The density of the foam may be in the range 20-35 kg/M3, or preferably, 25-35 kg/M3 and a particularly suitable density is in the range 28-30 kg/M3.

A particularly suitable foam is marketed under the trade name VRT 300 by British Vita Limited of Manchester. This foam has a density of 28-30 kg/M3 and when subjected to British Standard method of testing hardness according to B.S. 3667 has a hardness of 1 6-19 kg, and when subjected to British Standard method of testing hardness according to B.S. 4443 (N) has a hardness of 1 15--135 Newtons. This foam is a polyurethane foam of open-cellular form and has approximately 95% open cells and 5% closed cells. The density of the foam is generally uniform throughout -- VRT 300 has been found particularly suitable for use in rotary work-heads which are rotated at speeds of 1,400-2,000 r.p.m.

Since the sheet of backing material flexes when the base deforms locally the choice of backing material and the way it is secured to the base need to be carefully selected. Therefore, the backing material is preferably a P.V.C. sheet incorporating a fibre reinforcement, tarpaulin, or other material which is not likely to fray around the edge or edges when subjected to the strain and stresses involved. It is important that the adhesive used is flexible and remains steadfast regardless of the normal operating temperatures of the work-head.

Preferably, the base is at least 2.0 cm thick and is, preferably, of uniform thickness.

The first part of the work-head may comprise or include a plastics moulded attachment part which is attachable to a power take-off of a power driven device. The attachment is, preferably, by screw thread engagement, and where the work-head is a rotary work-head the first part may be a generally disc-shaped rigid body with a raised frusto-conical hub portion having a sleeve with an internal screw thread, said disc and hub portion, preferably, having been moulded in situ around said sleeve, and a central area of the disc, preferably, having a recess or having an aperture extending through the hub portion.A fault occurs in some rotary work-heads that the central portion of the workface of the base bulges outwardly at the centre through continued use due to stress factors and it is a second feature of the present invention that said first part may be designed to overcome this problem, by providing said recess or aperture as aforesaid to relieve pressure at the centre of the base.

The base, preferably, extends beyond the edge or edges of the first part and, where the workpiece is a rotary work-head, the base is, preferably, generally frusto-conical.

By the present invention a work-head is provided in which undesirable vibrational effects, such as chattering, may be aileviated.

An embodiment of a power-driven device having a work-head in accordance with the present invention will now be described, by way of example only, with reference to the accompanying illustrative drawings in which: Figure 1 shows in much simplified form the power driven device which is a power drill having a work-head attachment part; Figure 2 shows an enlarged section through the work-head, and Figure 3 shows an enlarged plan view of the work-head.

Figure 1 shows a power drill 1 having a removable rotary attachment work-head 2 which is generally disc-shaped (see Figure 3).

The drill 1 is a conventional drill having a revspeed of 1,400 to 2,000 r.p.m. and a power takeoff 1 a. Since the drill is of conventional form, it will not be described in further detail.

As shown more clearly in Figure 2 the workhead 2 has a base 3 comprising a layer of opencellular polyurethane resilient foam material such as that marketed under the trade name VRT 300, of which the physical characteristics have already been mentioned. The upper face 3a of the base 3 is secured by adhesion to a first generally discshaped rigid carrier part 4 of the work-head 2. The thickness of the foam material base 3 is approximately 2.5 cm for a nominal 6 inch (15 cms) or 8" (20 cms) diameter carrier part 4.

The carrier part 4 is of moulded plastics material and has a raised upwardly projecting frustoconical hub portion 4a surrounding a metal openended sleeve 4b which is internally threaded for attachment to a threaded rod 1 b of power take-off 1 a. The part 4 is injection moulded around the sleeve 4b in situ. The sleeve 4b has a bore 4c which extends all the way through the thickness of the carrier part 4. This is to relieve pressure on the centre of the base 3 to restrain the lower surface or work-face 3a bulging at the centre.

The base 3 is generally frusto-conical with the periphery of the base extending beyond the periphery of the carrier part 4, and providing a slightly arcuately concave profile in section, as illustrated. The lower surface or work-face 3b of the base is flat.

A disc-shaped thin sheet of flexible backing material 5 is secured by adhesive to the work-face 3b of the base 3.

The backing material 5 may be of any suitable form which will stand up to the stresses involved during a work operation which is described later.

In this embodiment, the backing material 5 is a fabric reinforced P.V.C. sheet and as such is not susceptible to fraying at the edges due to the edges of the abrasive sheet flexing during a work operation.

The backing material 5 is suitable for the reception of a self-adhesive abrasive sheet 6 so that the abrasive sheet may be firmly secured to the backing material but is removable therefrom once the abrasive sheet is worn out.

The adhesives used must be selected carefully so that they are flexible, heat resistant and provide adequate adherance or bonding throughout continued use of the work-head. A suitable adhesive for use in this example is that marketed under the name "SURESTIK" and given a code number 7557 by the Anglo-Chemical Company Limited.

In the embodiment described the work-head is removably attached to the power take-off but the power-driven device could be designed so that the work-head is not interchangeable with other attachments, and the power take-off may be any suitable form, for example a reciprocating rather than rotary take-off.

The operation of the work-head will now be described.

The power drill 1 may be held at any suitable angle to a workpiece (not shown) with the abrasive surface of the abrasive sheet 6 on the workpiece. As pressure is applied to the workhead 2 towards the workpiece whilst the workhead is rotated, a sanding, smoothing or polishing work operation may be performed on the workpiece. As the abrasive surface is moved relative to the workpiece, relieved or contoured areas of the workpiece may be operated op more uniformly since the base 3 will readily deform locally allowing the backing material 5 to flex with part of the abrasive sheet 6 out of the general plane X-X of the work-face 3b.The base 3 is capable of conforming substantially to the shape of the workpiece, surface even when the latter is deeply re-entrant or concave for example, and this is particularly important around the periphery or edge of the base 3.

Since the base 3 is soft, compressible and resilient just to the correct degree, where the edge of the abrasive sheet is used for sanding, smoothing or polishing, pressure is spread and there is no relatively hard edge provided by the base 3 which may cut into, and damage, the workpiece. This is particularly important in sanding down coats of paint on vehicle bodies. On the other hand base 3 is resilient enough to sustain the abrasive sheet in working operation with the work-piece and will not collapse thereby allowing the abrasive sheet to crease or tear.

Thus, a more uniform pressure may be applied to a workpiece using a work-head of the present invention with less regard to the contour of the workpiece.

Claims

1. A work-head comprising a base secured to a first, carrier, part of the work-head and a sheet of flexible backing material secured by adhesive to a planar work-face of the base, the backing material being suitable for attaching a self-adhesive abrasive sheet thereto and capable of flexing with part of an abrasive sheet secured thereto and with part of the work-face out of the general plane of the work-face, the material and dimensions of the base being selected to suit parameters of a work operation or work operations to be performed by the work-head, for example, speed of movement of the work-head and pressure application to the work-head while performing a work operation, the material of the base being soft, compressible and resilient so that:: (a) the base is capable of being locally deformed substantially over the entire area of the base including at the edge or edges of the base; (b) in use of the work-head with an abrasive sheet in performing a work operation, the base is capable of being deformed locally so that the abrasive sheet flexes with part of the backing material and part of the work-face moves out of the general plane of the work-face allowing the base to conform substantially to the shape of a workpiece being operated upon by the work-head.

(c) the base does not collapse during the workoperation, thereby allowing the abrasive sheet to crease or tear but is resilient enough to sustain the abrasive sheet in working operation with the workpiece.

2. A work-head as claimed in Claim 1 in which the first part of the work-head is rigid and, in use, the first part is movable under pressure towards the backing material thereby resiliently compressing the base allowing the first part to tilt or float relative to the backing material, when performing a work operation on a generally flat surface of a workpiece.

3. A work-head as claimed in Claim 1 or Claim 2 in which the base is a foam material for example of open-cellular form, for example, a polyurethane foam.

4. A work-head as claimed in Claim 3 in which the density of the foam is in the range 20-35 kg/M3.

5. A work-head as claimed in Claim 4 in which the foam density is in the range 25-35 kg/M3.

6. A work-head as claimed in Claim 5 in which the density is in the range 28-30 kg/M3.

7. A work-head as claimed in any one of Claims 3 to 6 in which the density of the foam is generally uniform throughout.

8. A work-head as claimed in any one of the preceding claims in which the base is at least 2.0 cm thick, of uniform thickness and extends beyond the edge or edges of the first part.

9. A work-head as claimed in any one of the preceding claims in which the backing material is a P.V.C. sheet incorporating a fibre reinforcement or a tarpaulin.

10. A work-head as claimed in any one of the preceding claims in which the first part of the work-head comprises or includes a plastics moulded attachment part which is attachable to a power take-off of a power driven device.

11. A work-head as claimed in Claim 10 in which the attachment is by screw thread engagement.

12. A work-head as claimed in any one of the preceding claims which is a rotary wprk-head.

13. A work-head as claimed in Claim 12 when dependent from Claim 11 in which the first part is a generally disc-shaped rigid body with a raised frusto-conical hub portion having a sleeve with an internal screw thread.

14. A work-head as claimed in Claim 13 in which said disc and hub portion have been moulded in situ around said sleeve, and a central area of the disc having a recess or having an aperture extending through the hub portion.

1 5. A work-head as claimed in any one of Claims 11 to 14 in which the base is generally frusto-conical.

1 6. A work-head substantially as herein described and illustrated with reference to Figures 2 and 3 of the accompanying drawings.

17. A power driven device including a workhead as claimed in any one of the preceding claims.

1 8. A power driven device substantially as herein described and illustrated with reference to Figure 1 of the accompanying drawings.

19. A method of sanding, smoothing or polishing a workpiece, said method comprising: (a) bringing a work-head having a base and a sheet of sanding, smoothing or polishing material secured thereto into working operation on a workpiece, said sheet being attached to a planar work-face of the base; (b) moving said work-head relative to said workpiece with said sheet in contact with the workpiece; ; (c) applying pressure on said work-head in a direction generally towards the workpiece during said relative movement, to resiliently locally deform the base so that part of the work-face moves out of the general plane of the work-face with a part of said sheet, said local deformation being adjacent a raised or relieved portion of the workpiece such that the base conforms substantially to said raised or relieved portion and facilitating sanding, smoothing or polishing said raised or relieved portion.

20. A method of sanding, smoothing or polishing a workpiece substantially as herein described with reference to the accompanying drawings.