GB2080192A - Rotary wooodworking tool - Google Patents

Abstract

In a rotary woodworking tool having an elongated cutter blade 1 received in a peripheral seating 8 of a solid cylindrical support 6, one end of the cutting edge of the blade is offset angularly from the other end of the cutting edge, e.g. at least mating faces of the seating and blade are helical, and a cutting angle A defined at any point along the cutting edge between a leading face of the blade and a radius through that point is the same for all points along the cutting edge. As the tool rotates, there is obtained a shearing action at successive points along the cutting edge, as distinct from simultaneous impact of all points of the cutting edge with the workpiece and individual small zones of the cell and fibre structure of the wood being severed at any instant are supported by adjacent such zones to each side, whereby there is obtained a cleaner surface finish. <IMAGE>

Description

SPECIFICATION Rotary woodworking tool This invention relates to a rotary woodworking tool of the kind in which a cutter blade, which is elongated in the direction of the axis about which it rotates, describes a path which is the surface of a cylinder. Such tools are com- rnonly used, for example, for tenoning and thicknessing of timber.

The cutter blade projects radially from a support, and the cutting edge is commonly formed between a plane face of the blade, at one side, and a bevelled face formed on the blade, at the other side.

It is usual to incline the cutting edge, that is to say the plane face which leads, in the direction of rotation, that is to say the plane face of the cutter blade is tilted, relative to the radial plane passing through the axis of rotation and the edge of the blade, by a small angle say of the order of 10-15".

Hitherto, the edge of the blade has been positioned along generator of the cylindrical path of movement, i.e. along a radial plane containing the axis of rotation. With such a tool, the entire length of the cutting edge comes into contact with the workpiece simultaneously, so that each small portion of the length of the cutting edge is acting on the cellular structure of the wood at the same instant that the adjacent portions at each side of that small portion are also contacting, compressing and severing the cells and fibres at the same time. Because of this simultaneous action, the cells and fibres receive little or no support from adjacent cells and fibres, considered along the line of cut.

It is known to reduce the value of the cutting angle as a method of minimising lifting and tearing of cells, and this can be successful to a limited extent, dependent upon features of grain and other characteristics of the wood. However, such reduction of the cutting angle is least effective where a small value of cutting angle is employed, e.g.

of the order of 10 , because of the relative loss of effective sharpness, and increased compressive stress on the cells in the plane of the cut. Moreover, grinding of edge portions of the blade may result in partial or entire removal of hardened edge portions of the blade.

The process of cutting wood with such a rotary tool involves severance of cells at the cutting edge, and their forcible deflection up the cutter face, and reduction of the cutting angle results in a proportionate increase of the resultant of the combination of vertical forces responsible for riving action on the cells, and compressive forces exerted in the direction of feeding, i.e. relative movement of the workpiece with respect to the tool. The vertical force acts parallel to the face of the cutter blade to overcome frictional resistance during severance, and force also acts perpendicular to the cutter blade face of deflection of the severed material. Change of cutting angle results in change of the relative forces.

It is the object of this invention to provide an improved form of rotary woodworking tool wherein, for a given cutting angle, the forces both parallel to and normal to the cutter blade face are reduced, and the cutting edge performs a shearing action in which each portion of the length of the cutter blade acts individually at an instant in time which is different from that instant at which its adjacent neighbouring portions act on the wood structure, such that each small zone of the wool structure being severed at any instant remains supported by adjacent zones of the wood structure at each side of it.

According to the present invention a rotary woodworking tool comprises a support having an axis of rotation and including a seating opening at its periphery and extending lengthwise of the axis, the seating being defined by a leading face and a trailing face, considered in the direction of rotation of the tool, and bottom face, the bottom face being of a same radius from the axis at any like point considered along its length, and a cutter blade received in said seating and projecting therefrom by a portion having a cutting edge, the blade having a leading face and a trailing face, the trailing face of the blade conforming to and contacting the trailing face of the seating, the leading face of the blade bounding the cutting edge of the blade being disposed and arranged such that at any point along the cutting edge of the blade the leading face of the blace at that point forms, with a radius passing through that point, a cutting angle as defined herein which is the same for all points, one end of the cutting edge being offset angularly from the other end of the cutting edge. In a preferred form, the trailing face of the seating and the trailing face of the blade are each a regular helix.

In a convenient construction, particularly where the seating is cut in a solid cylindrical support by means of a miliing cutter or the like, the leading and trailing faces of the seating are made parallel, considered at any point along their length.

The blade is advantageously made of strip or sheet metal, and accordingly the leading and trailing faces of the blade are likewise made parallel, considered at any point along their length.

As is conventional with cutter blades for rotary woodworking tools, the cutting edge of the blade may be defined by (i) the leading face of the blade, and (ii) a chamfer formed on the trailing face of the blade.

The blade would normally be removably received in the seating, and according to a further feature there are provided means for retaining the blade releasably in the seating, and such means may comprise a locking bar positioned against the leading face of the blade and having adjusting means abutting the leading face of the seating.

Means are advantageously provided for adjusting the radial projection of the blade from the support and for locating the blade in a selected position of projection.

In order that the nature of the invention may be readily ascertained, an embodiment of rotary woodworking tool in accordance therewith is hereinafter particularly described with reference to the figures of the accompanying drawings, wherein: Figure 1 is a perspective elevation of a cutter blade; Figure 2 is a perspective elevation of a rotary cutting tool including the blade of Fig.

1; Figure 3 is an end elevation of the cutting tool, to a larger scale, and Figure 4 shows an example of a blade.

Referring to Fig. 1 of the drawings, the cutter blade denoted generally by reference numeral 1 is made of strip metal and has a front face 2 and a rear face 3 which are generally parallel. The front face 2 is the face which leads, considered in the direction of rotation of the tool as a whole. The cutting edge 4 of the blade is formed by grinding a chamfer 5 on the rear face 3.

Referring now to Fig. 2, the support for the blade 1 is constituted by a solid metal cylinder 6. The structure of the support in the space 7 within the cylinder 6 is immaterial to the invention, and it will suffice to indicate that the cylinder 6 is rotatable about an axis X-Y and has any suitable bearing means and drive means, not shown.

The rotary cutting tool illustrated has two blades 1 situated at diametrically opposite positions, but the invention is not limited to this diametrical construction, and another number of blades could be utilised on a cylinder 6.

In the cylinder 6, for each cutter blade 1, there is formed a cutter seating slot 8 which is bounded by a leading face 9 and a trailing face 10, which are parallel, and a bottom face 21, at right angles to the faces 9 and 10. The faces 9, 10, considered at any radial plane along the axis of the cutting tool from one end to the other, are always at the same angle with respect to the respective plane passing through the axis of rotation. The slot 8 has a helical path, considered from end to end of the cutting tool, as seen in Fig. 2, and the cutter blade has a corresponding helical shape which exactly matches that of the slot 8, so that the rear face 3 of the blade 1 conforms to the shape of the trailing face 10 of the slot 8 and is in contact therewith over all of the area of the trailing face 10.The result of imparting the helical formation to the blade 1 in this manner is that the selected cutting angle "A", defined by a first plane containing the front face 2 of the blade and a plane containing the axis of rotation and the tip of the cutting edge, is the same for any small portion of the blade at any point along its length. The angle "A" might be, for example, 30".

The blade 1 is retained in the slot 8 by a locking bar 11 which extends the whole length of the blade 1, within the slot 8, and which is of somewhat smaller height so as to expose an adequate portion of the blade adjacent to the cutting edge 4.

The curved formation 11 a of the locking bar is provided for steering and guidance of the wood chips which are severed by the blade edge 4. The locking bar 11 is secured in the slot 8, and bearing against the blade 1, by means of a metal screws which are threaded into the locking bar 11 and which, after insertion of the bar, can be rotated by a spanner in the direction to cause them to emerge to a greater extent from the locking bar 11 and abut against the leading face 9 of the slot. The reaction force causes the locking bar 11 to be forced against the blade 1, and causes the blade 1 to be forced against the trailing face 10 of the slot 8. Such metal screws would be provided at intervals along the locking bar, but are not shown in these figures in view of the small scale of the illustration. Such screws are well known to the man skilled in this art.

The slot 8 has the same radial depth, of corresponding points of its bottom face 11, at any point considered along the length of the slot. Such a slot may conveniently be formed, in a cylinder 6 of solid metal, by securing the cylinder 6 on the worktable of a vertical milling machine, in such a manner that the cylinder 6 is rotatable about its own axis, and then causing the worktable to traverse along the direction of the axis of the cylinder whilst rotating the cylinder 6 at a constant rate.

The blade 1 need not necessarily seat on the bottom face 11 of the slot 8, but may be raised therefrom to a desired extent to obtain a desired radial projection of the cutting edge 4 from the cylinder 6. This lifting action may be obtained by tapered metal screws (not shown) which are threaded through caps on each end of the cylinder 6 and locate on the underside of the blade. According to the extent of threading in or out of the metal screws, the blade 1 is caused to ride up the tapering of the screws to a corresponding extent, and the radial projection of the cutting edge 4 can thus be adjusted.

The formation of the blade 1 in the manner described ensures that the cutting angle "A" is the same at any point along its length.

However, when the cutting tool is rotating, the positioning of the blade in the manner shown results in the adding of an axial com- ponent to the cut instead of it being solely circumferential, for each small portion of the cutting edge. As a result there is a shearing action, as distinct from simple impact of the blade edge on the wood, and each small portion of the wood structure is attacked by the cutting edge 4 at an instant which is different from the instant at which the neighbouring portions of the wood structure are attacked by the neighbouring portions of the cutting edge 4, whereby each portion of the wood structure remains supported at each side at the moment of severance.This results in a cleaner cutting action, with less liability of tearing of the wood structure, a phenomenon which is well known to occur where the rotary cutter has two or more blades which are each parallel to the axis of the tool.

In cutter blades for use in such woodworking rotary tools, it is known to form a front bevei of the cutting edge 4 on a portion of the general blade structure which has been specially treated to harden it, or which is provided as an insert of specially hard metal. As the blade 1 of the present invention is made in the helical form set forth, it is possible to maintain the cutting angle constant at all points along its length, i.e. the front face 2 can be left untouched, and only the usual bevel 5 is provided to form the cutting edge 4. This means in turn that it is not necessary to grind away the front face 2, and the specially hardened zone is retained fully intact.

In order to minimize or eliminate any lateral thrust which might be exerted on the workpiece, that is to say in the plane of the cut but at right-angles to the line of feed, a single cylinder 6 may be provided with two pairs of blades 1, the respective pairs being opposite hand, the blades of each pair being diametri cally opposite to each other, and the opposed pairs being 90 angularly offset.

The line of feed of the workpiece relative to the rotary cutter need not be precisely normal to the axis of rotation of the cutter, and the line of feed may be varied within limits to one side or the other of the normal.

Any number of blades may be provided on a single cylinder 6, in angularly spaced formation, but such spacing would be symmetrical and the cutter as a whole would be dynamically balanced.

According to the extent to which the helical path of the slot 8 is angled away from a generator line of the cylinder 6 parallel to its axis, the cutting edge 4 of the blade will be, at least over a major part of its length, of a substantially elliptical shape.

Claims (9)

1. A rotary woodworking tool comprising a support having an axis of rotation and including a seating opening at its periphery and extending lengthwise of the axis, the seating being defined by a leading face and a trailing face, considered in the direction of rotation of the tool, and a bottom face, the bottom face being at a same radius from the axis at any like point considered along its length, and a cutter blade received in said seating and projecting therefrom by a portion having a cutting edge, the blade having a leading face and a trailing face, the trailing face of the blade conforming to and contacting the trailing face of the seating, the leading face of the blade bounding the cutting edge of the blade being disposed and arranged such that at any point along the cutting edge of the blade the leading face of the blade at that point forms, with a radius passing through that point, a cutting angle as defined herein which is the same for all points, one end of the cutting edge being offset angularly from the other end of the cutting edge.

2. A rotary woodworking tool, as claimed in claim 1, wherein the trailing face of the seating and the trailing face of the blade are a regular helix.

3. A rotary woodworking tool, as claimed in either of claims 1 and 2, wherein the leading and trailing faces of the seating are parallel considered at any point along their length.

4. A rotary woodworking tool, as claimed in any one of claims 1 to 3, wherein the leading and trailing faces of the blade are parallel, considered at any point along their length.

5. A rotary woodworking tool, as claimed in any one of the preceding claims, wherein the cutting edge of the blade is defined by the leading face of the blade and a chamfer formed on the trailing face of the blade.

6. A rotary woodworking tool, as claimed in any one of the preceding claims, including means for retaining the blade releasably in the seating.

7. A rotary woodworking tool, as claimed in claim 6, wherein said retaining means comprises a locking bar positioned against the leading face of the blade and having adjusting means abutting the leading face of the seating.

8. A rotary woodworking tool, as claimed in any one of the preceding claims, including means for adjusting the radial projection of the blade from the support and for locating the blade in a selected position of projection.

9. A rotary woodworking tool substantially as described herein with reference to the accompanying drawings.