POWER PLANER

The present invention relates to hand held electric power tools and more particularly to power tools of the type which can be referred to as planers with one or more cutting edges arranged for rotation about an axis.

Hand held electric power tools for use in wood working are well known within the art and one such tool, typically referred to as a planer, is described within the Applicant's co-pending European patent application number 03255459.4, reference to which are incorporated herein. The present invention relates to an improvement to such tools.

When using a planer, a user must apply a component of force perpendicular to the surface which is to be planed, that is to say the user must press down on the planer during use in order to attain the required depth of cut. Ideally, the applied force would be constant during operation of the planer in order to achieve a smoothly planed surface which has planed, or had a depth of material removed, which is uniform along the length of the surface.

However the rotation of the planer blades around a cylindrical path results in an uneven force feedback to the user. Typically this is experienced by the user in the way of vibrations when operating the planer which makes it difficult for the user to apply a constant downward force during operation. The result is that it is difficult to achieve a smoothly planed surface, especially for those with less experience in the use of wood working tools.

It is known that the power tool form of planers typically include one or two blades provided to protrude from the cylindrical

surface of the rotatable drum which is driven about an axis substantially parallel to the surface to be planed. The drum is rotated by a motor mounted within the planer body and which is typically connected to the drum by a drive belt assembly. As the planer is moved along the work surface, the spacing between the respective blades around the drum surface means that the blades contacting the work surfaces causes an uneven scalloping effect as the planer is moved along the surface. This makes it difficult for the user to achieve the uniform smooth finish which they desire. The scalloping effect occurs as a function of the rotational speed of the blades as well as the speed at which the planer is moved across the work surface.

The scalloping effect can also be caused because each blade typically only cuts for a fraction of a revolution of the cutting drum, such that the blade is redundant for the remainder of the revolution, causing intermittent cutting of the worked surface and, as a result, at any given time there is the possibility that intermittently, no blade is positioned in contact with the workpiece surface and there is no cutting action, followed by a period when there is a cutting force applied due to the blade contacting the workpiece.

In view of the above problems, it is required for a user not only to apply constant and significant downward pressure to a planer during use, but also to move the planer at a specific and constant rate along the surface to be planed in order to try and obtain a sufficiently smooth finish by matching the movement of the planer along the surface with the rotational speed of the drum. When one considers that all of this must be achieved whilst the planer is vibrating during use, it will be appreciated that it is very difficult to achieve for any prolonged period of use.

The present invention aims to provide an improved hand held power tool planer which reduces the skill level required by the operator in order to achieve an even, uniform planed work surface.

According to the present invention in a first aspect there is provided a power tool planer comprising a housing, a motor disposed within the housing and a cutter body rotatably attached to the housing and arranged to be driven by the motor about an axis, wherein the cutter body has one or more cutting edges extending at least part way along the axis and spaced therefrom, wherein the one or more cutting edges are formed and/or positioned such that during rotation of the cutter body at least part of one of said cutting edges will always be available to be positioned in contact with a surface of a workpiece along which the tool is to be moved in use to perform a planing action.

The present invention is particularly advantageous in that the vibrations caused by a rotating cutting edge continually engaging and disengaging the worked surface are substantially reduced.

In one embodiment the cutting edges are formed such that prior to or simultaneously with one cutting edge disengaging from the work surface a further cutting edge contacts or is already in contact with the worked surface.

In one embodiment when one end of a cutting edge is disengaging the work surface, the other end of that cutting edge, or else of an adjacent cutting edge, is already in contact with the worked surface. Thus a smooth transition between cutting edges is achieved.

In one embodiment the one or more cutting edges are curved in their path across the cutter body.

Typically the cutter body has a length and each of the one or more cutting edges extends substantially along the entire length of the cutter body. Typically the cutting edge is elongate having a first end and a second end, the first end being located at a first end of the cutter body and the second end being located at a respective second end of the cutter body, with the intermediate portion of the cutting edge being curved at least part way around the circumference of the drum.

In this manner a smooth transition is achieved over the entire length of the cutter so as to produce a continuous cutting action. It will be appreciated that a hand held power tool of this kind has a cutter body, typically in the shape of a drum, which is relatively short in length. Therefore a relatively high degree of curvature of the cutting edge must be achieved in order for the cutting edge to pass around the required portion of the circumference of the drum in such a short length. This is difficult to achieve using conventional blades, especially since the blade must also have the structural rigidity to cut through a work surface at high rotational speeds.

Typically a straight line along the outer surface of the cutter body, arranged substantially parallel with the cutter axis, will cross at least one cutting edge between the ends of the cutter body. Typically the cutting edge remains spaced from the axis by a predetermined distance along the entire length of the cutter.

Preferably the cutter body is generally cylindrical in shape and may take the form of a drum. When two or more cutting edges are provided, the surface of the drum comprises a series of peaks and troughs so as to form discontinuities therein.

According to one embodiment, two of more cutting edges are equally spaced around the circumference of the cutter body. Preferably a series of three cutting edges are provided spaced by substantially 120° around the circumference of the cutter body. According to a preferred embodiment, a series of 6 cutting edges are provided at equal spacing around the circumference of the cutter body.

By providing multiple blades around the cutter, the required continuous cutting effect can be achieved without the need to arrange the blade at an acute angle relative to the cutting direction. In this manner the blade is arranged closer to perpendicular to the cutting direction in order to achieve a preferred angle of cut.

Preferably the torsion rate of the cutting edge is in the range of 1 -13 turns per meter. Yet more preferably still, the torsion rate of the cutting edge is between 1 -4 turns/m.

According to one embodiment the cutter body is provided with one or more slots or recesses for accommodation of a blade therein such that the cutting edge of the blade extends beyond the outer circumferential edge of the cutter body. The recess and the blade may be correspondingly shaped so as to fixedly hold the blade in place for cutting. In such an embodiment the blade may be clipped or snapped in place within the recess of the drum. Alternatively fixing means may be provided by way, for example, one or more screws.

In one embodiment the blade itself has a straight cutting edge which is then wrapped around the axis of the cutter so as to provide the curved profile. Typically the one or more blades are flexible and are pressed into position on the cutter by one or more shaped members. In a preferred embodiment, the shaped

members are plates which have been given the required curved profile such that when they are pressed against the cutting edge or blade, they deform the cutting edge the required amount around the axis . Typically the plates are pressed against the cutting edges by way of screws such that the plates both deform the cutting edge as well as holding the cutting edge securely against the cutter body.

In another embodiment the blade may have a substantially straight rearward edge and be provided with a curved forward cutting edge such that the rear edge of the blade can be attached in a substantially straight line across the length of the drum. Typically this type of blade will be attached at an angle to the axis of the cutter. This allows simplified attachment of the blade whilst the still providing for the curved or helical cutting edge according to the present invention.

In an alternative arrangement, the blades are integral with the drum such that they are permanently attached to the cutter body. In this embodiment the entire drum can be replaced in order to change the blades. The outer surface of the cutter body may include one or more discontinuities and the outer surface of the cutter body itself may be profiled in the region of the discontinuities in order to provide a cutting edge. In one particular embodiment the outer surface of the cutter body may be profiled to provide an outwardly extending lip which can be provided with a cutting edge attached to the lip. The cutting edge may be heat treated or otherwise hardened in a conventional manner.

According to a further aspect of the invention there is provided a cutter body for a hand held electric power tool.

Preferred embodiments of the present invention will not be described below in further detail with reference to the following figures in which:

Figure 1 shows a side view of a hand held electric power tool according to the prior art;

Figure 2 shows a cross sectional view of a hand held electric power tool according to the present invention;

Figures 3a-3c show different embodiments of a cutter for a hand held electric power tool according to the present invention; and,

Figure 4 shows a partial cross section of a cutting edge and cutter body arrangement according to a preferred embodiment of the present invention.

Turning firstly to the arrangement of figure 1 , there is shown in general a hand held electric power tool in the form of a hand held planer 10 according to the prior art. However it will be appreciated that the details of the cutter body and cutting edges are not shown within figure 1 and could equally be used in accordance with the present invention when provided with a cutting arrangement as shown in either figure 2 or figure 3.

The planer 10 in figure 1 includes a housing 12 which houses a motor 14. The housing 12 is provided with a front handle 16 and a rear handle 18 such that a user can securely hold the planer 10 during use. In particular, a user can grip the rear handle 18 and operate switch 20 so as to actuate the motor 14. A user may then apply pressure to the rear handle 18 in order to move the planer during operation in the direction of arrow A. At the same time a downward pressure can be exerted onto the

planer via front handle 16 so as to ensure the planer maintains the required contact with the work surface 22 during use.

The planer housing 12 also includes a cutter body housing portion 24 which contains a cutter body in the form of a drum 28 (see figures 2 and 3) within the housing for rotation about axis 26. Transmission means (not shown) extend between the motor housing 14 and the drum housing 24 such that output torque from the motor rotates the drum about axis 26 during use.

Figure 2 is a cross sectional view taken along the length of the planer 10 showing details of a cutter body or drum 28 partially enclosed within the drum housing 24. The cutter drum 28 is mounted on axle 30 such that when power is supplied to the motor 14 the drum 28 is rotated on the axle 30 about the axis 26.

The drum 28 in figure 2 is provided with a series of 3 cutting edges 32, the orientation of which is described in further detail below in relation to figure 3. The cutting edges 32 are formed as part of blades 34 which are held within correspondingly shaped recesses or slots 36 within the drum. The cutting edges 32 of the blades 34 extend beyond the circumference of the drum 28, such that when the drum is driven in a rotational manner about axis 26, the blades impinge on the worked surface 22 upon which the planer 10 is positioned, so as to remove a required depth of material from the surface 22.

In figure 3a, the cutter body 28 is provided with a single cutting edge 32 in the form of blade 38. The drum 28 has a first end 40 and an opposing end 42 which is spaced from the first end by the drum length L. The blade 38 extends the entire length of the drum between the first and opposing faces 40 and 42. In

addition the blade 38 is wrapped 360° or more around the outer surface of the drum. Thus when the blade 38 contacts the work surface 22 at the first end of the drum 40, it will simultaneously be in contact with the work surface 22 at the opposite end of the drum 42.

Figure 3b shows an arrangement with two blades which are separated by 180° around the circumference of the drum. Each blade 44 therefore curves around 180° or more in order to provide continuous cutting according to the present invention.

Figure 3c shows a drum 28 provided with three blades 46 which are spaced at 120° around the drum 28 such that the first end of one of the blades 46' overlaps with the opposite end of the adjacent blade 46" along a line 29 along the length of the drum.

Figure 3d shows an end view of the drum shown in figure 3a and it can be seen that the blade 38 extends around the entire circumference of the drum 28 and that the blade slot 36 at the first end of the drum 40 is therefore separated by 360° or more from the corresponding slot 36 at the opposite end of the drum 42.

Where 'n' is the number of cutting edges provided on the drum, it will be appreciated that each cutting edge must complete at least 1 /n turns of the cutting drum over the length L. Therefore the torsion rate of the cutting edge must be at least 1 /nL turns per meter.

It will be appreciated that by the application of the above criteria, a drum may be provided with any required number of cutting edges. In this manner a straight line drawn on the outer surface of the drum 28 parallel with the axis 26 will cross at least one blade along the length of the drum. Therefore the

cutting drum never loses contact with the work surface 22 during operation. The maximum number of blades which can be used is therefore limited only by practical considerations such as the dimensions of the blades and the drum as well as the associated manufacturing costs.

The blades in figures 3a-c may be formed as straight flexible metal blades which are wrapped around the drum 38 with the required curvature. Alternatively the blades may be formed with the required helical profile such that only a minor amount of deformation of the blade is required in order to insert the blade within the correspondingly shaped slot 36 in the drum.

In figure 4 a portion of the cutter body 28 is shown in cross section. The cutter body 28 is provided with a mounting surface 48, upon which a first side 49 of blade 50 is to be positioned for use. The blade 50 is flexible to a degree and is formed with a straight cutting edge 52. A fixing plate 54 is located against a second side 56 of blade 50 for use. Each of the cutter body 28, the blade 50 and the fixing plate 54 are provided with one or more apertures therein such that a screw 58 can pass through the fixing plate 54 and blade 50 into a threaded hole 60 within the cutter body. The screw is tightened to hold the blade 50 securely in place for use.

The mounting surface 48 is curved in shape such that it extends at least part way around the axis of the cutter body. In addition the fixing plate 54 is correspondingly curved in shape such that when the blade 50 is pressed between the fixing plate 54 and the mounting surface, it is deformed such that the cutting edge 52 follows the required curved or helical path around the cutter body axis .

When using a blade attachment method as shown in figure 4, it has been found that the continuous cutting effect of the present invention can be achieved using a combination of 6 blades spaced around the drum. For a standard drum length of 82mm, the torsion rate of the blades in a 6-blade arrangement will be 2.03 turns/m. A machined aluminium drum may be provided and a steel fixing plate is used to hold a relatively low-cost straight-edged blade in position. This offers one low cost way of realising the present invention such that the electric power tool is effectively cutting a worked surface for the entire 360° of each revolution of the cutter body.

Whilst the embodiment of figure 4 shows one way in which the blade may be held in position on the cutter body the skilled person will acknowledge that there are a number of alternative ways a cutting edge can be provided on a rotating cutting body. Such alternatives include producing a cutter body with integral cutting edges which are shaped, such as curved, around the body or else providing separate helical blades which can be attached to the cutter body using conventional techniques prior to use.

Thus by providing in accordance with the invention a cutter body as part of a powered planer tool, with the cutting edges arranged as described, .so a continuous cutting edge contact with the workpiece can be achieved. This allows the planing action which is achieved on the workpiece surface to be more uniform and have less opportunity for the scalloping effect and vibration to the user from the tool being caused as the tool is not experiencing the repeated engagement and disengagement of the cutting edges with the workpiece. It also means that the speed of movement of the planer along the surface is not as critical as with conventional planer power tools.