EP1726416A1

EP1726416A1 - Tool for working wood and its derivatives, and method to produce it

Info

Publication number: EP1726416A1
Application number: EP06114172A
Authority: EP
Inventors: Stefano Elia
Original assignee: Pozzo SpA
Current assignee: Pozzo SpA
Priority date: 2005-05-20
Filing date: 2006-05-18
Publication date: 2006-11-29
Anticipated expiration: 2026-05-18
Also published as: EP1726416B8; ITUD20050083A1; ES2329501T3; ATE435728T1; DE602006007642D1; EP1726416B1; PL1726416T3

Abstract

Tool (10) for working wood or its derivatives, and relative method to produce it. The tool (10) comprises a support element (11) substantially cylindrical and provided peripherally with a plurality of radial housing seatings (12), each housing a cutting blade (15). Each cutting blade (15) comprises an inclined upper surface (29) defining a determinate cutting profile (30) with at least an upper rake angle (γ1,γ2), which is variable along the cutting profile (30) according to each nominal diameter (D1, D2) of the cutting blade (15), the recovery angle (ε) and the mordant angle (α2, α2) formed between the cutting blade (15) and a radius of the support element (11) passing through the cutting profile (30).

Description

FIELD OF THE INVENTION

The present invention concerns a tool, such as for example a miller or suchlike, for working wood and its derivatives. The tool comprises a support element, or body, substantially cylindrical in shape, with which two or more cutting blades are radially associated, and clamping devices to clamp the latter to the body of the tool. To be more exact, each clamping device is able to maintain the nominal cutting diameter of the tool constant, even with cutting blades having different shapes and cutting diameters, after any sharpening operation.

BACKGROUND OF THE INVENTION

It is known that tools for working wood and its derivatives normally comprise a support element or body of the tool, provided radially with a plurality of housing seatings inside which an equal number of cutting blades are disposed. To be more exact, each cutting blade rests on a fixed shoulder made in the seating, and made so as to contrast the force imparted on the cutting edge by the working.
In each of the seatings a thrust element called wedge is normally mounted; thrust by a threaded grub screw, or drawn by a screw pressing on a plane rear surface of the blade, it acts against a bottom surface and a plane front surface of the cutting blade, keeping the latter positioned inside the relative seating.
Each cutting blade also has an upper surface, or back, shaped and inclined by a determinate upper rake angle γ, so as to define the cutting profile of the blade. The front surface and the back of the blade form a cutting angle β, normally less than 90° and defining a cutting edge of the blade, by means of which the chip is removed. Moreover, the radius of the support element that passes through the cutting edge of the blade defines with the front surface a mordant angle α.
Cutting blades are sharpened by removing material from the front surface of the blade, so as to restore the cutting edge, maintaining unchanged the cutting angle β. This operation, however, entails a reduction in the height of the blade, with a consequent proportional reduction in the cutting diameter of the tool, and a variation in the mordant angle α.
Different solutions are known to recover the positioning in height of the cutting blade, which generally provide that the bottom wall of the seating is inclined by a constant recovery angle ε, or calculated according to the mordant angle α of the blade, so that the wedge, sliding on the bottom surface, entails a proportional radial movement of the cutting blade, thus recovering the nominal cutting diameter.
However, known solutions, precisely because they provide a constant recovery angle ε, are reliable and precise only when the cutting blades have a single nominal diameter along the cutting profile. In this way, however, the mordant angle α varies, after sharpening, uniformly over the whole profile.
On the contrary, if the cutting blade is shaped, for example undulating, and has a cutting profile with different nominal diameters, the calculated recovery angle ε does not allow to recover all the diameters correctly, since the mordant angle α varies, after sharpening, differently for every diameter, and therefore not uniformly, thus entailing a progressive loss of precision of the tool.
A tool for working wood is also known, from the US patent US-A-4,541,756 , having a bottom surface resting directly on the bottom wall of the seating, and inclined parallel to the upper surface, or back, of the tool, so as to define a cross section substantially like a parallelogram. In this known solution, the tool is kept with its front surface against a relative support element by means of a screw disposed passing through the tool, screwed onto the support element, and acting on the plane rear surface of the tool.
In this way, after every sharpening, by facing the front surface of the tool, the position is recovered by the action of the screw element which, in cooperation with the inclined bottom surface of the tool, also recovers the radial positioning of the cutting edge.
For all types of clamping, shaped cutting blades also have inclined lateral surfaces with lateral rake angles ϕ, which define the lateral segments of the cutting profile which go from one diameter to the other.
In this case, both the solution shown in US-A-4,541,756 , and also the other known solutions, also entail a progressive error in the axial repositioning of the cutting profile, that is, along an axis parallel to the axis of rotation of the tool, causing differences in the shapings made on the pieces of wood, before and after sharpening.
These imprecisions in positioning are further accentuated when the cutting blades form, with the axis of rotation of the tool, an axial angle δ. In this case, in fact, the mordant angle α varies, not only because of the variation in diameter along the cutting profile, but also because of the axial angle δ itself, since the radiuses that define it are progressively more inclined according to the distance of the cutting profile from the axis of rotation of the tool.
One purpose of the present invention is to achieve a tool for working wood and its derivatives which, after the usual operations to sharpen the cutting blades, allows to maintain all the expected nominal diameters precisely constant, and to axially reposition the shaped cutting profile exactly in the original position, so that there are no variations in the shaping made on the wood, before and after sharpening.
Another purpose of the present invention is to achieve a tool which allows to recover with precision the positioning and nominal diameters of the cutting blades after they have been sharpened, even if their disposition is provided with an axial angle δ.
The Applicant has devised, tested and embodied the present invention to overcome the shortcomings of the state of the art and to obtain these and other purposes and advantages.

SUMMARY OF THE INVENTION

The present invention is set forth and characterized in the main claim, while the dependent claims describe other characteristics of the invention or variants to the main inventive idea.
In accordance with the above purpose, a tool for working wood and its derivatives according to the present invention comprises at least a support element, substantially cylindrical and provided peripherally with a plurality of radial housing seatings, each able to house a cutting blade and associated clamping means.
Each of the radial housing seatings comprises a reference surface against which the clamping means keeps the cutting blade clamped, and recovery means inclined by a recovery angle ε with respect to the reference surface, such as for example an inclined bottom surface, a lateral tongue, a guide pin, and with respect to which the clamping means is able to slide after the operations to sharpen the cutting blade.
The cutting blade comprises at least an inclined upper surface and defining a determinate cutting profile with at least an upper rake angle γ.
According to a characteristic feature of the present invention, the upper rake angle γ is variable along the cutting profile, according to each nominal cutting diameter of the tool, the recovery angle ε and each mordant angle α formed between the cutting blade and a radius R of the support element passing through the cutting profile.
In this way, a correct and precise recovery is guaranteed of all the nominal diameters of the cutting blade with a constant recovery angle ε, since the variability of the rake angle γ allows a uniform variation of the mordant angles α of every nominal diameter along the cutting profile, after the blade has been sharpened.
In the same way, even if an axial angle δ is provided between the cutting blade and the axis of rotation of the support element, the rake angle γ is in any case variable along the cutting profile, according to each mordant angle α, thus allowing to restore the cutting diameter along all the cutting profile with a constant recovery angle ε.
Moreover, the clamping means is conformed so as to keep the cutting blade clamped with a plane rear surface against the reference surface of the radial housing seatings, which gives the advantage of a wide contact surface between the blade and the tool body, so that the forces imparted by the working process on the cutting edge are discharged to a large extent onto the tool body, rather than transforming into shearing forces on the cutting edge, as happens, on the contrary, in the embodiment described in US-A-4,541,756 .
In a preferential form of embodiment, the cutting blade also comprises at least a lateral surface adjacent to the upper surface, inclined by a determinate lateral rake angle ϕ and defining a lateral segment of the cutting profile. In this case, the cutting blade also comprises at least a recovery surface inclined by a lateral recovery angle ε_lat substantially equivalent to the lateral rake angle ϕ, and able to rest against an abutment surface of the radial housing seating.
In this way, by taking the recovery surface, after sharpening, into contact with the abutment surface of the radial housing seating, an axial displacement is determined of the cutting blade with respect to the previous position, that is, along an axis substantially parallel to the axis of rotation of the support element.
Since the angle of lateral recovery ε_lat is substantially equivalent to the lateral rake angle ϕ, the axial displacement of the cutting blade is substantially equivalent to the reduction in the lateral surface of the cutting blade itself due to the sharpening, so that the original axial positioning of the cutting blade can be restored, and there are no differences in shaping on the wood worked, before and after the cutting blades have been sharpened.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other characteristics of the present invention will become apparent from the following description of a preferential form of embodiment, given as a non-restrictive example with reference to the attached drawings wherein:

fig. 1 is a plane view of a tool for working wood according to the present invention;
fig. 2 shows an enlarged view of a detail in fig. 1;
fig. 3 shows a lateral view of the tool in fig. 1;
fig. 4 shows a first form of embodiment of the cutting blade of the tool in fig. 1,
fig. 5 shows a lateral view of the cutting blade in fig. 4;
fig. 6 shows a plane view of the cutting blade in fig. 4;
fig. 7 shows a second form of embodiment of the cutting blade of the tool according to the invention.

DESCRIPTION OF A PREFERENTIAL FORM OF EMBODIMENT

With reference to the attached drawings, a tool 10 for working wood according to the present invention, comprises a support element 11, substantially cylindrical, rotary around an axis of rotation X and provided peripherally with a plurality of housing seatings 12, in this case three, equal to each other and able to house inside them a cutting blade 15 and a corresponding clamping device 16.
Each clamping device 16 comprises a thrust element 19 associated with an attachment grub screw 17, to attach the cutting blade 15 inside the respective housing seating 12.
Each cutting blade 15 comprises a shaped cutting profile 30, by means of which the chip is removed, a plane surface 25, a front surface 26, substantially parallel to the plane surface 25, a bottom surface 27 which connects below the plane surface 25 to the front surface 26, and two upper surfaces, or backs 29, in this case substantially horizontal, and each shaped with a determinate upper rake angle γ1, γ2. Each upper back 29 is inclined with respect to the front surface 26 by a determinate angle β, or cutting angle of the blade 15.
The cutting profile 30 is sharpened by means of removing a thickness sp of material from the front surface 26 of the cutting blade 15, so as not to vary the cutting angle β, but reducing the height of the cutting tool 15.
In this case, the cutting profile 30 has a first nominal cutting diameter D1 and a second nominal cutting diameter D2, smaller than the first. Moreover, the cutting blade 15 is provided with a surface, or lateral back 13, to connect the two diameters D1 and D2, shaped with a determinate lateral rake angle ϕ. The lateral back 13 is adjacent to the upper backs 29.
The cutting profile 30 is defined by the intersection edge between the backs 29 and the back 13, with the front surface 26 of the cutting blade 15.
The front surface 26 of each cutting blade 15 is inclined by a mordant angle α1, α2 with respect to a radius R of the support element 11, passing through the cutting profile 30. The mordant angle α1, α2 is different along the cutting profile 30, according to the nominal cutting diameter D1, D2.
As shown in figs. 4 to 6, the cutting blade 15 has a substantially square cutting profile 30 and therefore the upper 29 and lateral 13 backs define different segments with relative upper γ1, γ2 and lateral ϕ rake angles. On the contrary, if the cutting profile 30 has an undulating development, not shown, the upper 29 and lateral 13 backs and the relative upper γ1, γ2 and lateral ϕ rake angles are interpolated so as to give continuity to the shaping curve defined by the cutting profile 30.
Each cutting blade 15 also comprises a recovery surface 24 which laterally connects the plane surface 25 to the front surface 26, and which is kept by the clamping device 16 in contact with an abutment surface 23 of the housing seating 12.
According to the invention, the recovery surface 24 is inclined with respect to the front surface 26 by a lateral recovery angle ε_lat substantially equivalent to the lateral rake angle ϕ of the lateral back 13, so that after the removal of the thickness sp during sharpening, the cutting blade 15 is subjected, once repositioned in the housing seating 12, to an axial displacement Δj along an axis substantially parallel to the axis of rotation X of the support element 11.
The axial displacement Δj allows to recover axially the positioning of the cutting profile 30 after sharpening of the cutting blade 15, so that there is uniformity of shaping of the wood worked before and after the sharpening of the cutting blades 15.
Each housing seating 12 comprises a bottom surface 21, a reference surface 22 and the abutment surface 23, which is substantially orthogonal to the axis of rotation X of the support element 11.
The bottom surface 21 forms, as known for example from the European patent application EP-A-1.418.031 in the name of the Applicant, an obtuse angle with the reference surface 22. The amplitude of this obtuse angle is greater than 90° by a determinate recovery angle ε.
In this way, the thrust element 19, sliding below on the bottom surface 21 of the housing seating 12, progressively lifts the cutting blade 15 after every sharpening by a determinate value of radial recovery Δh.
According to a characteristic feature of the present invention, the method to produce the tool 10 provides at least a calculation step in which the upper γ1, γ2 and lateral ϕ rake angles are calculated so as to be variable along the cutting profile 30 according to each nominal diameter D1 or D2 of the recovery angle ε and of each mordant angle α1,α2 of the cutting blade 15.
This variability of the upper γ1, γ2 and lateral ϕ rake angles allows to recover with precision the nominal diameters D1 and D2 with a constant recovery angle ε.
To give an example, in one segment of the cutting profile 30 with a mordant angle αl and a nominal diameter D1, the step to calculate the upper rake angle γ1 provides the following substeps.
A first substep in which the initial coordinates (x1_init; y1_init) are calculated of the cutting profile 30 not yet sharpened, that is, still having the maximum thickness. In this step, having a nominal cutting radius $\frac{D 1}{2}$
and an initial mordant angle α1_init, the coordinates (x1_init; y1_init) are $x 1_{init} = \frac{D 1}{2} \cdot \sin (α 1_{init})$
and $y 1_{init} = \frac{D 1}{2} \cdot \cos (α 1_{init}) .$
A second substep in which the calculation is made of the final coordinates (x1_fin; y1_fin) of the cutting profile 30, that is, with the minimum usable thickness after the maximum sharpening. In this step, knowing the entity of the thickness sp removed during sharpening, firstly the final coordinate x1_fin is calculated, adding to the initial coordinate x1_init the entity of the thickness sp [x1_fin=x1_init+sp]; subsequently the final mordant angle α1_fin is calculated, dividing the final coordinate x1_fin by the nominal cutting radius $\frac{D 1}{2} [α 1_{fin} = \frac{x 1_{fin}}{\frac{D 1}{2}}]$
and finally the final coordinate y1_fin is calculated with the equation $y 1_{fin} = \frac{D 1}{2} \cdot \cos (α 1_{fin}) .$
A third substep in which, by means of the equation $Δ h 1 = \frac{D 1}{2} \cdot \tan (ε),$
the entity is calculated of the radial recovery value △h1 due to the recovery angle ε.
A fourth substep in which the values of variation (△x1; △y1) are calculated between the initial coordinates (x1_init; y1_init) and the final coordinates (x1_fin; y1_fin). Thus, the value of variation Δx1 is equivalent to the thickness sp [Δx1=sp], while the value of variation Δy1 appears from the difference between the initial coordinate y1_init and the final coordinate y1_fin added to the value Δh1 of radial recovery, that is Δy1=y1_init-y1_fin+Δh1.
At this point, in a fifth substep, the upper rake angle γ1 is calculated by means of the equation $γ 1 = \arctan (\frac{Δ y 1}{Δ x 1}) .$
In the same way, the upper rake angle γ2 is calculated, according to the diameter D2, the recovery angle ε and the mordant angle α2, and the lateral rake angle ϕ of the lateral back 13.
These steps to calculate the upper γ1, γ2 and lateral ϕ rake angles are equally valid if the cutting blade 15 is disposed on the support element 11 inclined by an axial angle δ (fig. 3) with respect to the axis of rotation X of the support element 11. In fact, in this case, the difference between the mordant angles α, apart from the possible variation in the nominal diameter D1 and D2, also depends on the progressive distance of the cutting profile 30 from the axis of rotation X and therefore, according to the invention, upper γ1, γ2 and, possibly, lateral ϕ rake angles are provided which are proportionally different.
Advantageously, these calculations to obtain the upper γ1, γ2 and, possibly, lateral ϕ rake angles are effected automatically by a profiling machine which produces the cutting blade 15.
In the form of embodiment shown in fig. 7, on the bottom surface 27 of the cutting blade 15 there is a positioning seating 31 provided with an inner surface 32 inclined with respect to the front surface 26 of the lateral recovery angle ε_lat, which is kept by the clamping device 16, in cooperation with a fixed abutment element 33, disposed transverse inside the housing seating 12, such as for example a pin 34, a screw or other.
In this way, it is possible to avoid working the recovery surface 24, thus reducing the production costs.
It is clear, however, that modifications and/or additions of parts may be made to the tool 10 as described heretofore, without departing from the scope of the present invention.
For example, according to a variant, instead of the threaded grub screw 17 a threaded screw stud may be provided, having the longitudinal axis substantially parallel to the front surface 26 of the cutting blade 15, and provided with a wedge profile, or ogive, by means of which pressure can be exerted on the thrust element 19 in order to take the cutting blade 15 against the reference surface 22, and keep the recovery surface 24 against the abutment surface 23 and possibly the inner surface 32 against the abutment element 33.
Moreover, according to the width of the cutting blade 15, instead of only one threaded grub screw 17, it is possible to provide several grub screws 17, to improve the pressure and grip of the thrust element 19 against the cutting blade 15.
According to a variant, the positioning seating 31 is made open on one side in correspondence with the recovery surface 24.
It also comes within the scope of the present invention to provide that instead of the bottom surface 21 there may be a guide element, not shown, such as for example a lateral tongue, a pin or suchlike, inclined by the recovery angle ε with respect to the reference surface 22, and able to guide the thrust element 19 and/or the cutting blade 15 during the steps of radial recovery of the value △h.
It is also clear that, although the present invention has been described with reference to specific examples, a person of skill in the art shall certainly be able to achieve many other equivalent forms of tool for working wood and its derivatives, and method to produce the same, having the characteristics as set forth in the claims and hence all coming within the field of protection defined thereby.

Claims

Tool for working wood or its derivatives, comprising at least a support element (11), substantially cylindrical and provided peripherally with a plurality of radial housing seatings (12) each able to house a cutting blade (15) and associated clamping means (16), wherein each of said radial housing seatings (12) comprises a reference surface (22), against which said clamping means (16) keeps said cutting blade (15) clamped, and recovery means (21), inclined by a recovery angle (ε) with respect to said reference surface (22) and with respect to which said clamping means (16) is able to slide, and wherein said cutting blade (15) comprises at least an inclined upper surface (29) defining a determinate cutting profile (30) with at least an upper rake angle (γ1, γ2), characterized in that said upper rake angle (γ1, γ2) is variable along said cutting profile (30) according to:
a) each nominal diameter (D1, D2) of said cutting blade (15);

b) said recovery angle (ε) and;

c) the mordant angle (α1, α2) formed between said cutting blade (15) and a radius (R) of said support element (11) passing through said cutting profile (30).
Tool as in claim 1, wherein said cutting blade (15) also comprises at least a lateral surface (13), which is adjacent to said upper surface (29), is inclined by a determinate lateral rake angle (ϕ) and is able to define said cutting profile (30) with said upper surface (29), characterized in that said cutting blade (15) also comprises at least a recovery surface (24) inclined by a lateral recovery angle (ε_lat) substantially equivalent to said lateral rake angle (ϕ), and able to be maintained by said clamping means (16) against an abutment surface (23) of said radial housing seatings (12).
Tool as in claim 2, characterized in that said cutting blade (15) also comprises a positioning seating (31) provided with at least an inner surface (32) inclined by said lateral recovery angle (ε_lat) and able to be maintained by said clamping means (16) against an abutment element (33) solid with said support element (11) and disposed inside said housing seating (12).
Tool as in any claim hereinbefore, characterized in that said clamping means (16) is conformed so as to keep a rear surface (25) of said cutting blade (15) against said reference surface (22).
Tool as in claim 4, characterized in that said rear surface (25) is plane and adjacent to said upper surface (29).
Method to produce a tool for working wood or its derivatives, comprising at least a support element (11) substantially cylindrical and provided peripherally with a plurality of radial housing seatings (12), each able to house a cutting blade (15) and associated clamping means (16), wherein each of said radial housing seatings (12) comprises a reference surface (22), against which said clamping means (16) keep said cutting blade (15) clamped, and recovery means (21), inclined by a recovery angle (ε) with respect to said reference surface (22) and with respect to which said clamping means (16) is able to slide, and wherein said cutting blade (15) comprises at least an inclined upper surface (29) defining a determinate cutting profile (30) with at least an upper rake angle (γ1, γ2), characterized in that it provides at least a calculation step wherein the different upper rake angles (γ1, γ2) are calculated along said cutting profile (30), according to each nominal diameter (D1, D2) of said cutting blade (15), of said recovery angle (ε) and of the mordant angle (α1, α2) formed between said cutting blade (15) and a radius (R) of the support element (11) passing through said cutting profile (30).
Method as in claim 5, characterized in that said calculation step provides at least the following substeps:
- a first substep in which the calculation is effected of the initial coordinates (x1_init; y1_init) of said cutting profile (30) with said cutting blade (15) not yet sharpened, that is, with the maximum thickness;

- a second substep in which the calculation is effected of the final coordinates (x1_fin; y1_fin) of said cutting profile (30), with said cutting blade (15) at its maximum sharpening, that is, with the minimum usable thickness;

- a third substep in which the entity is calculated of the radial recovery value (Δh1) due to said recovery angle (ε);

- a fourth substep in which the values of variation (Δx1; Δy1) are calculated between the initial coordinates (x1_init; y1_init) and the final coordinates (x1_fin; y1_fin), according to said value of radial recovery (Δh1); and

- a fifth substep, in which said upper rake angle (γ1) is calculated according to said values of variation (Δx1; Δy1).