WO2015164920A1

WO2015164920A1 - Random orbital sander

Info

Publication number: WO2015164920A1
Application number: PCT/AU2015/050194
Authority: WO
Inventors: Kevin Inkster
Original assignee: Arbortech Industries Limited
Priority date: 2014-05-01
Filing date: 2015-04-23
Publication date: 2015-11-05

Abstract

A sander mechanism (11) having a sanding head (15) mounted for rotation at one end of a spindle 17, with its axis offset from the spindle axis. The spindle (17) incorporates counterbalancing to dynamically balance the mechanism (11). The sander mechanism (11) has a sander head nominal diameter to counterbalanced shaft length that is square to over-square in configuration, and the sanding head (15) is capable of sanding with force applied in the same direction as the rotational axis of the spindle, through oblique, to across the axis, without biting into the work piece. In use, the spindle (17) is mounted to an angle grinder to provide a stable and easily controllable random orbital sander.

Description

Random Orbital Sander

Technical Field

[0001] This invention belongs to the field of tools for abrading, grinding and sanding. In particular, this invention relates to a random orbital sander.

Background Art

[0002] The following discussion of the background art is intended to facilitate an understanding of the present invention only. It should be appreciated that the discussion is not an acknowledgement or admission that any of the material referred to was part of the common general knowledge as at the priority date of the application.

[0003] A random orbital sander combines the action of a freely rotating disk sander with that of an orbital sander. In a random orbital sander, a sanding head is mounted for rotation in a driven spindle, with the rotational axis of the sanding head offset from and parallel with the rotational axis of the driven spindle. The typical offset of axes is around 3mm to 4mm.

[0004] In use while not under load, the sanding head will spin up to the speed of the driven spindle, but when loaded will slow down in rotational speed relative to the speed of the driven spindle. This slowing in speed results in the orbital action of the sanding head becoming random.

[0005] For best balance, handles by which the random orbital sander is grasped are best placed as low as possible, that is toward the plane of sanding action of the sanding head, rather than away from the plane of sanding action of the sanding head, in order to better balance the tool. The best balance is probably provided where the handles are located about the centre of weight of the tool, so that as much of the mass of the random orbital sander tool is located from the handles toward the plane of the sanding action, as is located away from the handles and the plane of the sanding action. If the handles are placed too far away from the plane of the sanding action, so that most of the mass of the tool is located from the handles toward the plane of the sanding action, the random orbital sander tool can get out of balance, resulting in the tool entering into a gyratory motion which can result in the random orbital sander digging in at the edges.

[0006] Random orbital sanders tend to be large flat sanders having a sanding disk of a minimum of from about 100 mm (4 inches) diameter to 150 mm (six inches) diameter, and are designed for flat surfaces or at best gently curved surfaces. The sanding pads of existing random orbital Sanders are mounted and as close as possible to the drive mechanism (driven spindle and motor) for reasons of balance. The balancing typically uses a simple counter-balance of the eccentric mass of the sanding head, located close to the sanding head and otherwise the tool utilises the high operating speed and resultant gyroscopic effect of the mass of the motor and tool when in operation to assist with balancing the tool. By necessity, such an arrangement requires the sanding head and mechanism located between the motor driving it to be under square; in other words the mechanism is much shorter than the width of the sanding pad.

[0007] A problem with random orbital sanders being large and flat means they cannot be used to deal with internal shapes or recesses within a work piece. Consequently, the traditional method of dealing with internal shapes is to use a small circular pad on a shaft driven rotationally by a drill or similar power tool. The two main problems with this method is that the rotating motion is very difficult to control in tight concave areas, and the high speed of the outer edge causes it to dig in, scour and gouge the surface.

Scouring is a particular problem with both rotational sanders and orbital sanders.

[0008] Throughout the specification unless the context requires otherwise, the word "comprise" or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

Summary of Invention

[0009] The inventor has developed a tool which can be used to abrade, grind and sand in a confined space such as in the working and finishing of internal shapes and recesses in a work piece, and avoid the problem with the outer edge digging in, scouring and gouging the surface as discussed above. Particularly the inventor has developed a random orbital sander than can achieve such working and finishing functions, and also abrade effectively, applying force in a direction obliquely to the rotational axis of the tool, and in certain embodiments, applying force up to normal to the rotational axis of the tool (i.e., in order to abrade and sand along the edge of the tool). The mechanical arrangement developed by the inventor is considered to potentially have broader application in random orbital sanders generally, which could allow for different

configurations of random orbital sanders to be developed for application beyond that presently envisaged by the inventor. The purpose of the current invention is to create an effective gentle or powerful sanding action both in the direction of or at right angles to the axis of the drive, thus allowing the benefits of random sanding to be used in deep confined, curved or contoured areas.

[0010] In accordance with one aspect of the invention there is provided a random orbital sander mechanism having a sanding head mounted for rotation at one end of a spindle, with the rotational axis of the sanding head offset from and parallel with the rotational axis of the spindle, wherein the spindle incorporates counterbalancing proximal to the sanding head, the counterbalancing comprising a first weight eccentricity located at a first distance along said spindle from the sanding head, the first weight eccentricity being within ±20% of the sanding head weight eccentricity and extending on the same side of the spindle as the sanding head offset, and the counterbalancing also comprising a second weight eccentricity in the spindle located between said sanding head and said first distance, the second weight eccentricity extending on the opposite side of the spindle and being within ± 10% of double the first weight eccentricity, the first distance being a length of from at least the same as the notional diameter of the sanding head. As a consequence, the random orbital sander mechanism is at least square to over square. This leads to a further advantage that extension shafts can be added between any motor and the random orbital sander mechanism, to extend the depth that the random orbital sander according to the invention can reach into.

[0011] The first weight eccentricity can be considered to be centred at a first position along the spindle. It should be understood that the second weight eccentricity may be the sum of several weights added or material excised at different positions along the spindle between the first position and the sanding head. Similarly the location of the first distance / first position can be considered the mean position along the spindle resulting from a plurality of weights added or material excised in order to form the first weight eccentricity. The result is that (preferably, save for any mass variation brought about by mass variation in sandpaper attached to the sanding head) the random orbital sanding mechanism is dynamically balanced and spins true to the spindle axis despite the eccentric mass of the sanding head.

[0012] In this description the term "weight" is used as in the common parlance and is intended to be equivalent to mass. Thus by the expression "weight eccentricity", a "mass eccentricity" is intended. This mass eccentricity results in in an out-of balance wobble or centrifugal effect when the spindle is rotated about its rotational axis.

[0013] By "notional diameter" of the sanding head, the diameter prescribed by the sanding head as it spins, is intended. The sanding head is typically circular, but may be triangular, square, or any other flat geometric shape, including rectangular, in order to allow specialised sanding operations, particularly to sand sharply into corners, which is an operation that normal rotary sanders and random orbital Sanders cannot perform. When the distance from the sanding head to the location of the first distance is referred to, the position from which this distance is measured is the sanding surface of the sanding head to the mean position of the location of the first distance.

[0014] Thus, more particularly, in accordance with the invention there is provided a random orbital sander mechanism having a sanding head mounted for rotation at one end of a spindle, with the rotational axis of the sanding head offset from and parallel with the rotational axis of the spindle, wherein the spindle incorporates counterbalancing proximal to the sanding head, the counterbalancing comprising a first weight eccentricity located at a first distance along said spindle from the sanding head, the first weight eccentricity resulting in a first centrifugal force under rotation of the spindle being within ±20% of the sanding head weight eccentricity centrifugal force and extending on the same side of the spindle as the sanding head offset, and the counterbalancing also comprising a second weight eccentricity in the spindle located between said sanding head and said first distance, to counterbalance the first centrifugal force and the sanding head weight eccentricity centrifugal force, the first distance being a length of from at least the same as the notional diameter of the sanding head. This results in a dynamically balanced spindle that spins substantially true to its axis in free space despite the offset of the rotational axis of the sanding head.

[0015] It will be understood that the second weight eccentricity gives rise to a centrifugal force extending on the opposite side of the spindle and preferably it is within ± 10% of double the first weight eccentricity centrifugal force.

[0016] Also in accordance with the invention there is provided a random orbital sander mechanism having a sanding head mounted for rotation at one end of a spindle, with the rotational axis of the sanding head offset from and parallel with the rotational axis of the spindle, wherein the spindle and sanding head are dynamically balanced by counterbalancing in said spindle proximal to the sanding head, and wherein the most distal counterbalancing in said spindle from said sanding head is located at a length of from at least the same as the notional diameter of the sanding head.

[0017] Preferably said spindle includes a coupling at the end opposite to said one end by which said spindle is driven by a motor. The coupling may be a screw thread, so that the spindle may be driven by tools such as an angle grinder, a router, or a drill.

Alternatively extension shafts may be fitted between the spindle and the motor. [0018] Where there is difficulty determining the position of the weight eccentricity, the centre of the position of the eccentricity shall be taken to be the position. As will be seen, in the embodiments, the weight eccentricities are formed by machining material from the spindle, conveniently by machining half-flats into the spindle, but they could be equally made by drilling and tapping the spindle in the appropriate position and fitting a machine screw of the desired weight. In either case, the centre-point for the weight eccentricity along the spindle shall be the point the first distance and distance for the position of the second weight eccentricity are measured. The weight eccentricity extends on the side of the spindle opposite the machined flats.

[0019] Preferably the first distance is a length of from one to four times the diameter of the sanding head.

[0020] Preferably the first distance is a length of from one to three times the diameter of the sanding head.

[0021] Preferably the first distance is a length of from one and a half to three times the diameter of the sanding head.

[0022] Preferably the first distance is a length of from one and a half to two and a half times the diameter of the sanding head.

[0023] Preferably the first distance is a length of from one and a half to two times the diameter of the sanding head.

[0024] The second weight eccentricity in the spindle is preferably located spaced from said first weight eccentricity.

[0025] Preferably the second weight eccentricity in the spindle is located spaced substantially equidistant between said sanding head and said first weight eccentricity.

[0026] Preferably the first weight eccentricity is within ±15% of the sanding head weight eccentricity.

[0027] Preferably the first weight eccentricity is within ±10% of the sanding head weight eccentricity.

[0028] Preferably the first weight eccentricity is within ±5% of the sanding head weight eccentricity. [0029] Ideally the first weight eccentricity is substantially the same as the sanding head weight eccentricity.

[0030] Preferably the second weight eccentricity is within ± 5% of double the first weight eccentricity.

[0031] Preferably the second weight eccentricity is double the first weight

eccentricity.

[0032] Ideally the second weight eccentricity would counterbalance both the sanding head weight eccentricity and first weight eccentricity. This results in a dynamically balanced spindle that spins substantially true to its axis in free space despite the offset of the rotational axis of the sanding head.

[0033] Preferably the first weight eccentricity centrifugal force is within ± 15% of the sanding head weight eccentricity centrifugal force.

[0034] Preferably the first weight eccentricity centrifugal force is within ±10% of the sanding head weight eccentricity centrifugal force.

[0035] Preferably the first weight eccentricity centrifugal force is within ±5% of the sanding head weight eccentricity centrifugal force.

[0036] Ideally the first weight eccentricity centrifugal force is substantially the same as the sanding head weight eccentricity centrifugal force.

[0037] Preferably the second weight eccentricity centrifugal force is within ± 5% of double the first weight eccentricity centrifugal force.

[0038] Preferably the second weight eccentricity centrifugal force is double the first weight eccentricity centrifugal force.

[0039] Ideally the second weight eccentricity would counterbalance both the sanding head weight eccentricity and first weight eccentricity, resulting in a dynamically balanced spindle that spins substantially true to its axis in free space despite the offset of the rotational axis of the sanding head.

[0040] It will be understood that the sanding head weight eccentricity is taken to include all out of balancing introduced by the offset axis of the sanding head relative to the axis of the spindle, together with weight eccentricity due to the weight of the sandpaper attached to the sanding head. Variations in weight of sandpaper disks means that exact balancing may not be realistically achieved.

[0041] The sanding head should be balanced about its rotational axis, save for any imbalance that might be introduced by incorrect affixing of abrasive paper.

[0042] The sanding head preferably includes a resiliently deformable material which acts as a cushion for a sandpaper disk which is attached thereto, to the contact side of the cushion. Attachment may be by contact adhesive or hook and loop fasteners. In another arrangement abrasive material such as garnet may be bonded directly to the cushion on the contact/sanding side of the cushion.

[0043] Preferably the elasticity of the cushion is from 30 to 60 durometer on the Shore A scale. Elasticity of from 40 to 50 durometer should prove effective in most applications.

[0044] Preferably the cushion is circular in configuration and flat across at least 20% of its contact surface, the contact surface extending normal to the rotational axis of the sanding head.

[0045] Preferably the cushion is flat across at least 25% of its contact surface. [0046] Preferably the cushion is flat across at least 30% of its contact surface. [0047] Preferably the cushion is flat across at least 35% of its contact surface. [0048] Preferably the cushion is flat across at least 40% of its contact surface. [0049] Preferably the cushion is flat across at least 45% of its contact surface. [0050] Preferably the cushion is flat across at least 50% of its contact surface. [0051] Preferably the cushion is flat across at least 55% of its contact surface. [0052] Preferably the cushion is flat across at least 60% of its contact surface. [0053] Preferably the cushion is flat across at least 65% of its contact surface. [0054] Preferably the cushion is flat across at least 70% of its contact surface.

[0055] Preferably the cushion is flat across at least 75% of its contact surface.

[0056] Preferably the cushion is flat across at least 80% of its contact surface. [0057] Preferably the cushion is flat across at least 85% of its contact surface.

[0058] Preferably the cushion is flat across at least 90% of its contact surface.

[0059] Preferably the cushion is flat across at least 95% of its contact surface.

[0060] Preferably the cushion is flat across all of its contact surface.

[0061] The cushion may be of constant thickness, and backed by a plate member which attaches to a bearing mount to fit said sanding head to said spindle. The cushion may extend outwardly from the edge of the plate member to provide an edge of the sanding head that exhibits greater deformability during use than the portion of the cushion backed by the plate member.

[0062] The plate member and cushion may be circular, but other shapes including triangular, square, rectangular, pentagonal, hexagonal, etc. are possible. A triangular or square shape would be expected to prove suitable for sanding into sharper corners.

[0063] The cushion may be flat across all of its contact surface, except for the edge which may be tapered. The tapering of the edge may be on the non-contact side of the cushion, that is the side of the cushion away from the side to which sand paper or the like is attached. This allows for a greater flexure at the edge of the cushion, allowing the formation of curved surfaces at the edge of the cushion.

[0064] Preferably the edge of the contact side of the cushion is formed with an outwardly extending annular flange, continuous with the contact side of the cushion so that the contact side is flat to its periphery, the outwardly extending annular flange extending around the circumference of the cushion.

[0065] Preferably the outwardly extending annular flange is of constant thickness terminating in a flat circumferential edge. The outwardly extending annular flange provides a region of greater flexibility around the edge of the cushion, for deflecting during sanding operations, than does the provision of a tapered edge.

[0066] Preferably the edge of the cushion is formed with a concave circumferential recess extending continuously from the outwardly extending annular flange opposite the contact side. This arrangement allows the outwardly extending annular flange to deflect smoothly under force applied during a sanding operation, when running up against a raised surface in the workpiece. [0067] Preferably the concave circumferential recess bisects the outwardly extending annular flange and a second outwardly extending annular flange extending from the non- contact side of said cushion, the diameter of the second outwardly extending annular flange being less than the diameter of the outwardly extending annular flange.

[0068] Preferably the concave circumferential recess is a half round shape in radial cross-section, and its depth from the edge of the second outwardly extending annular flange is about the circumference of said half round shape. Alternatively the concave circumferential recess may be a V-shape.

[0069] Preferably the radius of the outwardly extending annular flange exceeds the radius of the second outwardly extending annular flange by more than two thirds of the thickness of the cushion in proximity to the concave circumferential recess. This ensures that on full deflection of the outwardly extending annular flange under force applied during a sanding operation, when running up against a raised surface in the workpiece, the deflection of the outwardly extending annular flange is limited by coming into contact with the edge of the second outwardly extending annular flange.

[0070] Preferably the radius of the outwardly extending annular flange exceeds the radius of the second outwardly extending annular flange by about the thickness of the cushion in proximity to the concave circumferential recess. The radius of the outwardly extending annular flange can be greater than this, but there is not much advantage believed to be gained from doing so.

[0071] The arrangement described above allows the motor that drives the spindle to be located spaced away from the sanding head, and in particular the sanding surface. This allows the random orbital sander to reach deep into confined spaces. It is possible to include a further drive shaft between the spindle and the motor, without further counterbalancing, providing of course that the further drive shaft is balanced, allowing even deeper reach into confined spaces.

[0072] Preferably the offset of the rotational axis of the sanding head from the rotational axis of the spindle is at least 0.5 mm.

[0073] Preferably the offset of the rotational axis of the sanding head from the rotational axis of the spindle is at least 0.7 mm.

[0074] Preferably the offset of the rotational axis of the sanding head from the rotational axis of the spindle is from 0.7 mm to 6 mm. [0075] Preferably the offset of the rotational axis of the sanding head from the rotational axis of the spindle is from 0.7 mm to about 5 mm.

[0076] Preferably the offset of the rotational axis of the sanding head from the rotational axis of the spindle is from 0.7 mm to about 4 mm.

[0077] Preferably the offset of the rotational axis of the sanding head from the rotational axis of the spindle is from 0.7 mm to about 3 mm.

[0078] Preferably the offset of the rotational axis of the sanding head from the rotational axis of the spindle is from 0.7 mm to about 2 mm.

[0079] Preferably the offset of the rotational axis of the sanding head from the rotational axis of the spindle is from 0.7 mm to about 1.5 mm.

[0080] Preferably the offset of the rotational axis of the sanding head from the rotational axis of the spindle is from 0.8 mm to about 1.2 mm. In practice, this range of offset has proven to provide unexpected sanding performance benefits. It has been found that once the offset reaches 1.5 mm, the tool becomes less stable.

[0081] Preferably the offset of the rotational axis of the sanding head from the rotational axis of the spindle is about 1.0 mm.

[0082] Preferably the sanding head has a diameter of from 25 mm to 100 mm.

[0083] Preferably the sanding head has a diameter of from 25 mm to 75 mm.

[0084] Preferably the sanding head has a diameter of from 25 mm to 60 mm.

[0085] Preferably the sanding head has a diameter of from 30 mm to 55 mm.

[0086] Preferably the sanding head has a diameter of from 35 mm to 40 mm.

[0087] Preferably the sanding head has a diameter of about 38 mm.

[0088] In accordance with a second aspect of the invention, there is provided a cushion for a sanding head for a disk sander or a random orbital sander, the cushion being formed of a resiliently deformable material, the cushion being flat across all of its surface on the contact (sanding) side and formed with an outwardly extending annular flange continuous with the contact side of the cushion so that the contact side is flat to its periphery, the outwardly extending annular flange extending around the circumference of the cushion. [0089] Preferably the outwardly extending annular flange is of constant thickness terminating in a flat circumferential edge.

[0090] Preferably the edge of the cushion is formed with a concave circumferential recess extending continuously from the outwardly extending annular flange opposite the contact side thereof. This arrangement allows the outwardly extending annular flange to deflect smoothly under force applied during a sanding operation, when running up against a raised surface in the workpiece.

[0091] Preferably the concave circumferential recess bisects the outwardly extending annular flange and a second outwardly extending annular flange extending from the non- contact side of said cushion, the diameter of the second outwardly extending annular flange being less than the diameter of the outwardly extending annular flange.

[0092] Preferably the concave circumferential recess is a half round shape in radial cross-section, and its depth from the edge of the second outwardly extending annular flange is about the circumference of said half round shape.

[0093] Preferably the radius of the outwardly extending annular flange exceeds the radius of the second outwardly extending annular flange by more than two thirds of the thickness of the cushion in proximity to the concave circumferential recess. This ensures that on full deflection of the outwardly extending annular flange under force applied during a sanding operation, when running up against a raised surface in the workpiece, the deflection of the outwardly extending annular flange is limited by coming into contact with the edge of the second outwardly extending annular flange.

[0094] Preferably the radius of the outwardly extending annular flange exceeds the radius of the second outwardly extending annular flange by about the thickness of the cushion in proximity to the concave circumferential recess. The radius of the outwardly extending annular flange can be greater than this, but there is not much advantage believed to be gained from doing so.

[0095] The cushion may be of constant thickness, and backed by a plate member which attaches to a bearing mount to fit said sanding head to said spindle.

[0096] In accordance with a third aspect of the present invention, there is provided a sanding head for a disk sander or a random orbital sander, including a cushion as described above. [0097] In accordance with a fourth aspect of the present invention there is provided a sanding head for a random orbital sander comprising a resiliently deformable cushion backed by a plate member, the contact surface of the cushion extending normal to the rotational axis of the sanding head, and the contact surface of the cushion extending beyond the periphery of the plate member to present an edge of the sanding head that presents greater deformability during use than the portion of the cushion backed by the plate member.

[0098] The cushion may be flat across all of its contact surface, except for the edge which may be tapered. The tapering of the edge may be on the non-contact side of the cushion, that is the side of the cushion away from the side to which sand paper or the like is attached. This allows for a greater flexure at the edge of the cushion, allowing the formation of curved surfaces at the edge of the cushion.

[0099] Preferably the edge of the contact side of the cushion is formed with an outwardly extending annular flange, continuous with the contact side of the cushion so that the contact side is flat to its periphery, the outwardly extending annular flange extending around the circumference of the cushion.

[00100] Preferably the outwardly extending annular flange is of constant thickness terminating in a flat circumferential edge.

[00101] Preferably the edge of the cushion is formed with a concave circumferential recess extending continuously from the outwardly extending annular flange opposite the contact side.

[00102] Preferably the concave circumferential recess bisects the outwardly extending annular flange and a second outwardly extending annular flange extending from the non- contact side of said cushion, the diameter of the second outwardly extending annular flange being less than the diameter of the outwardly extending annular flange.

[00103] Preferably the concave circumferential recess is a half round shape in radial cross-section, and its depth from the edge of the second outwardly extending annular flange is about the circumference of said half round shape.

[00104] Preferably the radius of the outwardly extending annular flange exceeds the radius of the second outwardly extending annular flange by more than two thirds of the thickness of the cushion in proximity to the concave circumferential recess. [00105] In accordance with a fourth aspect of the invention, there is provided a random orbital sander incorporating a random orbital sander mechanism as described above.

[00106] In operation, a random orbital sander incorporating the mechanism according to the invention, exhibits superb controllability without getting out of balance, and does not bite into the workpiece at the edges. The random orbital sanders according to the invention are capable of maintaining natural stability while sanding a surface that extends obliquely from right angles to the rotational axis of the spindle. The sanding head with the cushion according to the second aspect of the invention described above provides an arrangement that can form smooth transitioning from a flat surface to a curved surface in a workpiece. In addition and particularly advantageously, the random orbital sander with the sanding head according to the second aspect of the invention can sand a surface along the edge of the cushion. This sanding head can sand a surface extending from normal to the rotational axis of the spindle, through angles oblique to normal to the rotational axis of the spindle, up to parallel to the rotational axis of the spindle. When applied at right angle to the axis of the drive, the flexible pad first exerts a gentle force to the workpiece as the outward extending annular flange folds, but can then exert a powerful sanding action when the outward extending annular flange comes into contact with the perimeter of the second outwardly extending annular flange and further force is applied. The folding outward flange concept only works with a random orbital action because the sanding head stops rapid rotation (though continues rotating very slowly with a random orbital action) while a standard rotary action would quickly destroy the abrasive disc.

Brief Description of Drawings

[00107] A preferred embodiment of the invention with three preferred embodiments of sanding head will now be described in the following description of a random orbital sander attachment to fit an angle grinder, made with reference to the drawings, in which:

Figure 1 is a perspective view from above of the random orbital sander attachment fitted to an angle grinder fitted with a sanding head according to a first embodiment;

Figure 2 is a perspective view from above of the random orbital sander attachment fitted to an angle grinder fitted with a sanding head according to a second embodiment;

Figures 3, 4 and 5 are side elevations of a third angle orthographic projection showing the random orbital sander attachment according to the embodiment;

Figure 6 is a bottom view of the sanding head fitted to the random orbital sander attachment according to the embodiment, showing some hidden detail; Figure 7 is a cross section through section C-C, looking down, of figure 4;

Figure 8 is a perspective view from below of the random orbital sander attachment according to the embodiment;

Figure 9 is a perspective view from above of the random orbital sander attachment according to the embodiment;

Figure 10 is a cross-section view through the random orbital sander attachment;

Figure 11 is an exploded perspective view from below of the random orbital sander attachment;

Figure 12 is a side elevation of the random orbital sander attachment with sanding head according to the first embodiment;

Figure 13 is a side elevation of the random orbital sander attachment with sanding head according to the second embodiment;

Figure 14 is a perspective view from above of a cushion and sanding head according to a third embodiment;

Figure 15 is a cross-section through the cushion of the sanding head according to the third embodiment, in operation;

Figure 16 is a close-up view of detail A of figure 15;

Figure 17 is a close-up view of detail A, showing partial deflection of the edge of the contact side of the cushion; and

Figure 18 is a close-up view of detail A, showing full deflection of the edge of the contact side of the cushion;

Figure 19 is a perspective view from below of a cushion and sanding head according to a fourth embodiment;

Figure 20 is an exploded perspective view the cushion and sanding head of figure 19;

Figure 21 is a perspective view from above of a cushion and sanding head according to a fifth embodiment;

Figure 22 is a perspective view from above of a cushion and sanding head according to a sixth embodiment;

Figure 23 is a perspective view from above of the random orbital sander attachment with the cushion and sanding head according to the fifth embodiment, fitted to an angle grinder; and

Figures 24 and 25 are side elevations of a third angle orthographic projection showing the random orbital sander attachment with cushions according to the third and fourth embodiments. Description of Embodiments

[00108] The embodiments shown in figures 1 and 2 are a random orbital sander mechanism in the form of an attachment 11 for use with an angle grinder 13. The attachment 11 is intended for use by woodworkers for sanding and sculpting wood 14, particularly fine work and work having internal recesses.

[00109] Referring to figures 3 to 9, the attachment 11 has a sanding head 15 mounted for rotation in a spindle 17 at one end 18 thereof, with the rotational axis 19 of the sanding head 15 offset from and parallel with the rotational axis 21 of the spindle 17. The amount of offset is 1.0 mm, resulting in a possible maximum orbit of 2.0 mm.

[00110] The spindle 17 incorporates counterbalancing proximal to the sanding head 15, the counterbalancing comprises a first weight eccentricity in the form of a first slot 23 located at a first distance 25 along the spindle 17 from the sanding head 15, and a second weight eccentricity in the form of a second slot 27 in the spindle 17 located between the first slot 23 and the sanding head 15. The centre of the second slot 27 is located half way between the centre of the first slot 23 and the end

[00111] The first weight eccentricity provided by the first slot 23 is in the same radial direction as and commensurate with the weight eccentricity introduced by the offset of the sanding head 15, and the second weight eccentricity provided by the second slot 27 is in the opposite radial direction to that provided by the first slot 23, to counterbalance the first weight eccentricity and the of sanding head weight eccentricity. Thus the amount of material removed to form the second slot 27 is double in weight to that removed to make the first slot 23. The effect of the counterbalancing is to dynamically balance the spindle 17 and sanding head 15, so that the spindle 17 spins substantially true to its axis 21 in free space despite the offset of the rotational axis of the sanding head.

[00112] The sanding head 15 has a diameter of 38 mm, and the distance from the sanding surface of the sanding head 15 to the centre of the first weight eccentricity provided by the first slot 23 is about 60 mm, making the configuration of sanding head to the counterbalancing weight eccentricity well over square, by a nominal ratio of about 1 : 1.5.

[00113] Referring to figures 9 and 10, at the opposite end 31 of the spindle 17 is an aperture 33 having a female thread 35 machined therein, formed along the central axial extent 21 of the spindle, to allow the spindle to be screwed onto the male thread of the angle grinder 13. As will be seen later, extension shafts can be fitted between the spindle 17 and the angle grinder 13, to extend the reach of the sanding head 15, providing the extension shafts are properly balanced about their rotational axes.

[00114] At the end 18 of the spindle 17, a bearing housing 37 and head recess 39 are machined into the spindle 17 with their central axis 19 parallel to the spindle axis 21 and offset by 1.0 mm. A circlip recess 41 is also machined into the inside wall of the bearing housing 37, to receive a circlip 43 to retain two ball bearing assemblies 45 in place, when the sanding head 15 is fitted.

[00115] Referring to figures 10 and 11, the sanding head 15 has a mounting pin 47 with a head 49 at one end, an intermediate cylindrical surface 51 to receive the ball bearing assemblies 45 in an interference fit, and an outer cylindrical end 53 of reduced diameter to receive a collar 55 via its aperture 56 in press fit manner. Flats 57 machined on opposite sides of the collar 55 allow the collar to be held by a spanner, and provide access to the circlip 43.

[00116] A plate member in the form of a sanding head backing plate 59 is secured in a threaded aperture 61 in the mounting pin 47, by a slotted machine screw 63. The collar 55 is held by its flats 57 by a spanner as the machine screw 63 is tightened, to secure the sanding head backing plate 59 to the mounting pin 47.

[00117] A resilient cushion 67 having sloping sides 69 broadening out to a flat contacting surface 71 is bonded by its non-contact side 72 to the flat surface 73 of the sanding head backing plate 59. A sandpaper disk 75 with self adhesive backing is adhered to the flat contacting surface 71 of the resilient cushion 67, to complete the sanding head 15. In an alternative arrangement, hook and loop fasteners such as Velcro ™ may be used to secure the resilient cushion 67 to the flat contacting surface 71

[00118] The resilient cushion 67 is made of rubber which is sufficiently firm to provide a flat surface to support the sandpaper disk 75, but flexible so that the edges of the cushion 67 will deflect, allowing smoothly transitioning curves to be sanded into wood being sculpted, as shown in figure 12. It can be seen that in all of the embodiments the edges of the cushion 67 extend beyond the periphery of the backing plate 59. This imparts a greater flexibility to the cushion 67 at the edges, compared with where the cushion 67 is supported by the backing plate 59, which provides superior performance in sanding transitioning curves while sculpting with the attachment 11.

[00119] The resilient cushion 67 of the sanding head of the second embodiment is shown in figures 2 and 13. This resilient cushion 67 has a flat contacting surface 71 with convex edges 77 exhibiting a curvature and sloping in the opposite direction to the sloping sides 69 of the first embodiment.

[00120] The resilient cushion 67 of the sanding head of the third embodiment is shown in figures 14 to 18. This resilient cushion 67 is about 5.8 mm thick and has a flat contacting surface 71 with an outwardly extending annular flange 79 continuous with the contacting surface of the cushion so that the contacting surface 71 is flat to its periphery 81. The outwardly extending annular flange 79 extends around the circumference of the resilient cushion 67. The outwardly extending annular flange 79 has a diameter of 50 mm and is of constant thickness being 2 mm thick and terminating in a flat

circumferential edge 83.

[00121] The edge of the resilient 67 cushion is formed with a concave circumferential recess 85 extending continuously from the surface 87 of the outwardly extending annular flange 79 opposite the contacting surface 71.

[00122] The concave circumferential recess 85 bisects the outwardly extending annular flange 79 and a second outwardly extending annular flange 89 extending from the non- contact side of the resilient cushion, the diameter of the second outwardly extending annular flange 89 being 38 mm (12 mm less than the diameter of the outwardly extending annular flange 79).

[00123] The concave circumferential recess 85 is a half round shape in radial cross- section, with a diameter of about 1.8 mm, and its depth from the edge of the second outwardly extending annular flange is about the circumference of the half round shape.

[00124] This arrangement allows the outwardly extending annular flange 79 to deflect smoothly under force applied during a sanding operation, when running up against a raised surface in the workpiece. As can be seen in figures 17 and 18, the outwardly extending annular flange 79 deflects when sanding a sloped surface relative to the plane of the flat contacting surface 71, and deflects to a point where the surface 87 contacts with the exposed edge of the second outwardly extending annular flange 89, which allows a greater force to be applied to the workpiece.

[00125] The resilient cushion of the third embodiment is backed by a plate member in the form of a backing plate 59, in the same manner as the first and second embodiments, the top surface of the top section is bonded to a backing plate 59 in the same manner as illustrated in the first two embodiments. A circular piece of sandpaper is attached to the contacting surface, to extend at least as far as the flat circumferential edge 83. [00126] The rubber pad of cushion 67 is divided into three layers being the top section (the second outwardly extending annular flange 89) of about 38mm and 2mm in depth; a middle waist section (the concave circumferential recess 85) of slightly less diameter than the top section and usually radiused to connect the top section to the bottom section; and the bottom section (the outwardly extending annular flange 79) of about 50mm diameter and 2mm depth.

[00127] The middle section may in some circumstances be eliminated altogether but its diameter, depth and radius of the profile may be changed or tuned to suit the desired flexibility of the rim of the bottom section as it encounters a surface. The desired flexibility may also be effected by changing the durometer rating of the cushion 67 or the thickness of the bottom section.

[00128] The profile of the circular rubber pad is such that the wider section may bend if it encounters a surface substantially parallel to the drive axis and if pressure is applied in the direction of the surface, the rim attached to the abrasive bends until it encounters the top section whereupon significantly greater force can be applied to abrade the surface.

[00129] The resilient cushion and sanding head of the fourth embodiment is shown in figures 19 and 20, and is functionally the same as the third embodiment, but also includes a bush 91 having an integrally formed annular flange 93 at one end, in order to secure the sandpaper disk 75 to the cushion 67. With this arrangement, the sandpaper disk 75 does not require adhesive backing.

[00130] An in-hex countersunk machine screw 95 extends through the bush 91. The bush 91 extends through an aperture 97 formed in the sandpaper disk 75 and through an aperture 98 formed in the cushion 67 so that the screw 95 and bush 91 can secure the backing plate 59 to the mounting pin 47. The bush 91 is slightly shorter than the depth through the cushion 67, so that the flange 93 will secure the sandpaper disk 75 to the cushion 67, and compress the cushion 67 so that the flange 93 and the machine screw 95 are sunk below the surface of the sandpaper disk 75, so as to not interfere with the work piece during a sanding operation.

[00131] The sanding head 15 according to the fifth embodiment is the same as the fourth embodiment in features but is triangular rather than circular. It has the same peripheral extending flange 79a, but the flange is not annular. The surface 87 of the flange 79a contacts the exposed edge of the second outwardly extending flange 89 only at the corners 99 of the sanding head 15. The flange 79a extends along the straight sides 100 of the sanding head, and its reach is sufficient to meet the second outwardly extending flange 89 along the straight sides 100, on all sides 100 of the sanding head 15. In use the sandling head will spin so that all of its corners 99 prescribe a nominal diameter for the sanding head but when the sanding head meets sufficient resistance against a workpiece 14 the angular rotation will slow and an orbital action will commence (as is the case in all of the embodiments). If the sanding head 15 stalls, as it will if sufficient downward force is supplied, or a straight edge 100 meets an incline, upward transition or wall in the workpiece 14, the flange 79a and sandpaper 75 along the straight side 100 may be urged against the an incline, transition or wall. With sufficient sideways urging across the axis of the rotation of the spindle 17, the flange 79a will be urged to flex upwardly until its upper surface 87 meets the peripheral edge 89 of the second outwardly extending flange 89, allowing the user to apply a greater force to the workpiece 14, normal to the rotational axis of the spindle 17. Referring to figure 23, a corner 99 of the sanding head 15 may be urged into a point 101 where two walls 102 in the workpiece 14 meet, to allow the corner 103 between the walls 102 to be sanded more sharply than could be achieved with the circular sanding heads of the first four embodiments When the top 87 of the flange 79a meets the peripheral edge 89 of the second outwardly extending flange 89, the user can apply greater force into the corner 103 across the rotational axis of the spindle 17.

[00132] The sanding head of the sixth embodiment is similar to that of the fifth embodiment except that the flange 79b is present only at the corners 99. There is no flange present along the sides 100 of the head 15 (other than what is formed by the sandpaper 75. As such, the sanding action along the edge 100 of the sanding head 15 is not as pronounced as the fifth embodiment. The flange 79b will deflect upward when the corner 99 of the sanding head meets a corner 103 in the workpiece 14, until the top 87 of the flange 79a meets the peripheral edge 89 of the second outwardly extending flange 89, allowing the user to apply greater force into the corner 103 across the rotational axis of the spindle 17.

[00133] The elasticity of the rubber used in the cushion of all embodiments is 40 durometer, on the Shore A scale. Elasticity of from 30 to 60 durometer would be expected to prove effective in most applications, and from 40 to 50 durometer is most suitable.

[00134] The embodiments provide a random orbital sander with a relatively small sanding head, that fits as an attachment to standard angle grinders by threading onto the drive spindle. Apart from the smaller size sanding head, it differs from other random orbital sanders in that the sanding head is positioned well away from the head (motor and hand grips) of the grinder on a narrow spindle. The sanding head can be positioned at least 100mm from the grinder head.

[00135] The narrow spindle allows the sander to work in deep confined spaces and needs to be dynamically balanced to counter the offset mass of the sanding head and bearings. The spindle can be further extended by the addition of further extension shafts 101 which can be simple turned shafts which do not require further balancing. All metal parts of the tool can be turned from tool steel.

[00136] An example of an extension shaft 111 is illustrated in figures 19 and 20, attached to the spindle 17 of an attachment 11. The extension shaft 111 has a male threaded stud which extends into end 31 the spindle 17 and engaged with the female thread 35 and tightened. Two machined flats 113 allow a spanner to engage the extension shaft 111. The other end 115 of the extension shaft is provided with the arrangement of aperture 33 and female thread 35, in the same manner as that of the spindle to allow the extension shaft 111 to be fitted to an angle grinder. This detail can be seen in figure 10.

[00137] The extension shaft 111 shown in the drawings is the same length as the spindle 17; however, an extension shaft can be any practical length, providing that it is not so long that it gets out of balance due to flexure.

[00138] In operation, when the spindle 17 is driven (rotated along its central axis) by the grinder, the sander head also tends to rotate because of the friction of the bearings; however, if it is brought into contact with a surface, the friction of the contact with the surface is much greater than the friction of the bearings so the head ceases rotating but is forced by the offset mounting position to move in a random orbital manner.

[00139] The effect of this invention is that very powerful and effective sanding can be applied to deep internal shapes such as bowls, vases and other complex internal shapes. A gentle or powerful sanding action can be applied at right angles to the drive axis, which is something that hitherto has not been achieved by conventional random orbital senders.

[00140] It should be appreciated that the scope of the invention is not limited to the specific embodiments disclosed herein, and the skilled addressee will understand that changes may be made without departing from the spirit and scope of the invention.

Claims

The Claims Defining the Invention are as Follows

1. A random orbital sander mechanism having a sanding head mounted for rotation at one end of a spindle, with the rotational axis of the sanding head offset from and parallel with the rotational axis of the spindle, wherein the spindle and sanding head are dynamically balanced by counterbalancing in said spindle proximal to the sanding head, and wherein the most distal counterbalancing in said spindle from said sanding head is located at a first distance being a length of from at least the same as the notional diameter of the sanding head.

2. A random orbital sander mechanism having a sanding head mounted for rotation at one end of a spindle, with the rotational axis of the sanding head offset from and parallel with the rotational axis of the spindle, wherein the spindle incorporates counterbalancing proximal to the sanding head, the counterbalancing comprising a first weight eccentricity located at a first distance along said spindle from the sanding head, the first weight eccentricity resulting in a first centrifugal force under rotation of the spindle being within ±20% of the sanding head weight eccentricity centrifugal force and extending on the same side of the spindle as the sanding head offset, and the

counterbalancing also comprising a second weight eccentricity in the spindle located between said sanding head and said first distance, to counterbalance the first centrifugal force and the sanding head weight eccentricity centrifugal force, the first distance being a length of from at least the same as the notional diameter of the sanding head.

3. A random orbital sander mechanism having a sanding head mounted for rotation at one end of a spindle, with the rotational axis of the sanding head offset from and parallel with the rotational axis of the spindle, wherein the spindle incorporates counterbalancing proximal to the sanding head, the counterbalancing comprising a first weight eccentricity located at a first distance along said spindle from the sanding head, the first weight eccentricity being within ±20% of the sanding head weight eccentricity and extending on the same side of the spindle as the sanding head offset, and the counterbalancing also comprising a second weight eccentricity in the spindle located between said sanding head and said first distance, the second weight eccentricity extending on the opposite side of the spindle and being within ± 10% of double the first weight eccentricity, the first distance being a length of from at least the same as the notional diameter of the sanding head.

4. A random orbital sander mechanism as claimed in any one of claims 1, 2 or 3 wherein said spindle includes a coupling at the end opposite to said one end by which said spindle is driven by a motor.

5. A random orbital sander mechanism as claimed in any one of claims 2 to 4 wherein the weight eccentricities are formed by machining material from the spindle at said first distance and at a second position located between said sanding head and said first distance.

6. A random orbital sander mechanism as claimed in any one of the preceding claims wherein the first distance is a length of from one to four times the diameter of the sanding head.

7. A random orbital sander mechanism as claimed in claim 6 wherein the first distance is a length of from one and a half to two and a half times the diameter of the sanding head.

8. A random orbital sander mechanism as claimed in any one of claims 2 to 7 wherein the second weight eccentricity in the spindle is located spaced from said first weight eccentricity.

9. A random orbital sander mechanism as claimed in claim 9 wherein the second weight eccentricity in the spindle is located spaced substantially equidistant between said sanding head and said first weight eccentricity.

10. A random orbital sander mechanism as claimed in any one of claims 2 to 9 wherein the first weight eccentricity is within ±10% of the sanding head weight eccentricity.

11. A random orbital sander mechanism as claimed in claim 10 wherein the first weight eccentricity is within ±5% of the sanding head weight eccentricity.

12. A random orbital sander mechanism as claimed in any one of claims 2 to 11 wherein the second weight eccentricity is within ± 5% of double the first weight eccentricity.

13. A random orbital sander mechanism as claimed in claim 12 wherein the second weight eccentricity is double the first weight eccentricity.

14. A random orbital sander mechanism as claimed in any one of the preceding claims wherein the sanding head includes a resiliently deformable material which acts as a cushion for a sandpaper disk which is attached thereto, to the contact side of the cushion.

15. A random orbital sander mechanism as claimed in claim 14 wherein the cushion is backed by a plate member extending normal to the rotational axis of the sanding head, and extends outwardly beyond the edge of the plate member to provide an edge of the sanding head that exhibits greater deformability during use than the portion of the cushion backed by the plate member.

16. A random orbital sander mechanism as claimed in claim 14 or 15 wherein the edge of the contact side of the cushion is formed with an outwardly extending annular flange, continuous with the contact side of the cushion so that the contact side is flat to its periphery, the outwardly extending annular flange extending around the circumference of the cushion.

17. A random orbital sander mechanism as claimed in claim 16 wherein the outwardly extending annular flange is of constant thickness terminating in a flat circumferential edge.

18. A random orbital sander mechanism as claimed in claim 16 or 17 wherein the edge of the cushion is formed with a concave circumferential recess extending

continuously from the outwardly extending annular flange opposite the contact side.

19. A random orbital sander mechanism as claimed in claim 18 wherein the concave circumferential recess bisects the outwardly extending annular flange and a second outwardly extending annular flange extending from the non-contact side of said cushion, the diameter of the second outwardly extending annular flange being less than the diameter of the outwardly extending annular flange.

20. A random orbital sander mechanism as claimed in claim 19 wherein the concave circumferential recess is a half round shape in radial cross-section, and its depth from the edge of the second outwardly extending annular flange is about the circumference of said half round shape.

21. A random orbital sander mechanism as claimed in claim 19 or 20 wherein the radius of the outwardly extending annular flange exceeds the radius of the second outwardly extending annular flange by more than two thirds of the thickness of the cushion in proximity to the concave circumferential recess.

22. A random orbital sander incorporating a random orbital sander mechanism as claimed in any one of the preceding claims.