High speed hand sawing machine and saw disc therefor

Abstract: The invention relates to a high speed hand tool provided with a saw disc (1,14) which has less than ten teeth (2), preferably four, each tooth (2) having a radial flank (8), which preferably inclines forward in the cutting direction, and a tangential flank, which has a small clearance angle (b). The teeth may have a greater thickness than the disc itself which thickness, in that case, diminishes in a direction opposite to the direction of rotation. In another embodiment the teeth are offset alternately to the right and the left. The invention also comprises an adjustable protective device, which enables to set the depth of a perpendicular saw cut.

Description: The invention relates to a saw disc with saw teeth spaced around an outer circumference thereof, which form part thereof or are separate saw teeth permanently connected thereto, each of said saw teeth having a cutting edge formed by an adjacent radial flank and an adjacent tangential flank. Such a saw disk is known from for example EP-A-0 072 642 and DE-A-33 05 113. With these known saw disks the clearance behind the saw teeth is defined by the outwardly protruding saw teeth itself and the depth gauge is defined by an circular arc between successive teeth with two different radii. The aim of the invention is to provide such a saw disk which, however, can be manufactured far more easily and for considerably less costs. According to the invention the above purposes are realized by providing that the tangential flank defines a circular arc and forms a clearance angle with a path of movement of the cutting edge about a centre of the disc, wherein a distance between a centre of the circular arc and the centre of the disc ranges from 0,06 to 0,3 times a distance from the cutting edge to the centre of the disc, the centre of the circular arc being located beside a bisector of a portion of the disc bounded by radii of the disc taken at two successive cutting edges. With the saw disk according to the invention the tangential flank of a saw tooth defines a single circular arc which runs from the cutting edge of that saw tooth to the recess in front of the next saw tooth. The radius of the circular arc and the centre thereof are chosen such that directly behind the cutting edge a clearance space is defined and that following the clearance the distance between the circular arc and the circle through the cutting edges of the saw teeth diminishes to a predetermined distance. In this manner the end of the circular arc defines a depth gauge that controls the depth of the cut of the next saw tooth. It has appeared that a good cutting operation can be obtained when the radial flank at the cutting edge inclines forward in the direction of rotation. Said radial flank does not necessarily have to be straight, but for instance may have a curved shape, which has the advantage that with the manufacturing of saw discs according to the invention in small series the material in front of the radial flank may be removed by drilling. Preferably the radial flank inclines forward at the cutting edge at an angle between -5° and +15°. According to a further elaboration of the invention it is provided that the tangential flank has a clearance angle relative to the path of movement of the cutting edge. Preferably the clearance angle lies between 2° and 5°. The most important advantage thereof is that the teeth may be sharpened repeatedly by filing without having a noticeable effect on the radius of the saw disc. Moreover, with a curved radial flank, the sharpening may be effected by means of a round file or a rat's-tail. According to still a further elaboration of the invention. it is provided that the tangential flank lies on a circular arc, the centre of which lies at a distance from the centre of the disc of 0.06 to 0.3 times the distance from the outer end of the radial flank to the centre of the disc, and which is located beside the bisector of the radii of the disc through two successive cutting edges. This embodiment has the advantage that behind the cutting edge of a tooth first an increasing space appears followed by an again decreasing space till relatively near the radial edge of the next tooth. By that it is prevented that the teeth have a too great in-feed. Preferably the number of teeth is four, specifically with discs with a diameter of 15-30 cm. However it is also possible to work with less teeth and it is even possible to saw in a reasonable manner with only one tooth (in which case the disc in fact may consist of only an arm), but larger numbers than four give disadvantages rather than advantages, more in particular with respect to the larger number of teeth that possibly have to be sharpened. An embodiment, with which also in the direction perpendicular to the disc a clearance is realized, provides that the teeth have a greater thickness perpendicular to the disc at their cutting edge than the remaining part of the circumference of the disc, which greater thickness diminishes gradually behind the cutting edge to the thickness of the remaining part of the circumference of the disc. Preferably the angular distance, over which a tooth has a greater thickness than the remaining part of the circumference of the disc, is about 10° to 20°. Such a disc may be manufactured by grinding or turning material from the middle of the disc till near the edge. Next part of the edge can be removed, for instance when the radial clearance is made by way of grinding. With an embodiment of the disc according to the invention, with the disc having the same overall thickness, it is preferably provided that, in a way known per se, the teeth are offset alternately in opposite direction from the plane of the disc. Preferably the set of the teeth is about 0.1 - 1.0 mm. With saw tests it has appeared that the thickness of the disc has little influence on the sawing results, but evidently that a disc with a smaller thickness gives a smoother saw cut and requires less energy. In practice the thickness of the disc is chosen as thin as can be consistent with a good stability of the disc. Discs made of steel or rust resistant steel gave good results with a thickness from 1.0 to 3.0 mm. The material of the saw disc according to the invention preferably has to meet the requirement that it has a satisfactory hardness, but not such a hardness that it is no longer possible to file it. This is the case with for example abrasion and rust resistant steel, for example chromium steel. Finally a disc with the tooth shape according to the. invention may also be provided with teeth of abrasion resistance material, such as widia. However the advantages of easily sharpening are lost therewith, while also the impact load resistance, when hitting a material of a too great hardness, is hardly maintained, because a broken widia tooth commonly results in a disc which no longer is usable. A tool as described in the preamble has to be provided with a protective device, which at least guards one side of the disc. According to a further elaboration of the invention it can be provided that, with application of the invention, that is as saw, the protective device has an opening to let pass a segment of the saw disc, which opening lies in a plane parallel to the axis of rotation of the saw disc. This offers the possibility to obtain a saw cut perpendicular to a flat part of the object to be worked. According to a further elaboration of the invention it can be provided that the distance from the plane to the centre line of the axis of rotation is adjustable. This offers the possibility to give the saw cut a predetermined depth, for example for the sawing of rabbets. The invention also comprises a guard suitable to be mounted on a tool according to the invention as claimed in claims 21-23. 5 The invention is elucidated in the following on basis of the drawing, in which: fig.1 schematically shows a side view of a saw disc according to the invention; fig.2 shows a radial. view thereof; fig.3 shows a corresponding view of another embodiment; fig.4 shows a view of the saw disc with the protective device for it; not being part of the present invention. fig.5 shows a side view of the protective device according to fig.4, and fig.6 shows a lower view of said protective device. In fig.1 a steel disc is indicated with 1, provided with four teeth 2, which have a slightly larger thickness than the disc, as appears from fig.2. The teeth are preceded by a recess 3, which preferably is slightly larger than a semi-circle. The original circle shaped circumference of the disc is indicated with 4, A being the centre of said circumference forming circle. As can be seen from the drawing said circle goes through the cutting edge, which is indicated with the point 5 of the cutting teeth. From point 5 of the cutting edge, shown in the upper right, a circular arc is drawn with centre B, which is located somewhat beside the bisector of the radii from A to both cutting edges 5 and below the centre A. Point B has been chosen such that a predetermined in-feed 6 is left clear and furthermore that the edge 7 of the disc from right to left is located first at the level of a cutting edge 5, then deflects inwardly from the circular shape and finally, near the next cutting edge 5, is located at a distance of approximately the total in-feed within the circle through the cutting edges 5. As can be seen further the cutting edges 5 have a front flank or radial flank 8, which encloses an angle "a" with the radius of the circle. The clearance angle relative to the path of the cutting edge is indicated with "b". It will be clear that with the filing of the recess 3 almost the same radius of the saw disc will be kept, and that a change will be noticeable only after a large part is filed away, for example one centimetre. In practice this will rarely happen, because it has appeared that with a disc according to the invention, made of abrasion or rust resistant steel, it is possible to saw wood for a very long time without the teeth getting unsharpened. For the sake of clarity the maximum in-feed 6 and the angles "a" and "b" are drawn on an enlarged scale. Fig.2 shows a view along line II-II of fig.1. From this can be seen that the edges 2 of the cutting teeth provide a cutting edge 5 with a greater width than that of the disc. Fig.3 shows a view of a set tooth with a cutting edge 5 and a recess 3 with a boundary 9. As is shown in fig.4 the protective device not being part of the present invention consists of a first part 10, with a hood shaped upper part 11, two vertical walls 12 and a vertical back wall 13. Disc 14, which is provided with four cutting teeth 15 and recesses 16 in front of the teeth, has a hole 17 with which it fits over axis 18, to which it is fastened by means of nut 19. The wall 13 is fastened to the housing of a not shown rotary tool around axis 18 with a not shown clamping ring. The protective device comprises a second part 20 with a vertical wall 21 and a horizontal plane 22. In said plane, as is indicated in fig.6, an oblong slot is made, through which a segment of disc 14 protrudes. A relatively large space for disc 14 is left out in slot 23, as a result of which a possible line, along which should be sawed, can be seen easily. As can be seen more in particular from the side view of fig.5, in which the same parts are indicated with the same references as before, a slot 24 is provided in the side walls 21, with a wing screw 25, which is screwed in the side walls 12 of part 10 and with a guiding pin 26, which is also mounted on wall 12. By loosening the wing screws on either side of the protective device part 11 may be moved relative to part 20, as a result of which the depth may be adjusted with which the disc protrudes through opening 23. The shown protective device not only is saver than a guard as is commonly used with grinding tools, with which bottom 22 is missing, but besides the adjusting possibility with slots 24 and wing screws 25 also gives the possibility to saw in perpendicular direction with a desired cutting depth very well. Although the teeth of the described shape, made of abrasion or rust resistant steel, have a long working life when sawing wood and the like and can be sharpened by filing with for example a rat's-tail in a very short time, it is also possible to use teeth made of hardmetal. This is more expensive than forming the teeth out of the disc itself, but will give a longer working life, opposite thereto is that when hitting a nail. the possibility exists that a widia teeth becomes damaged irreparable. The combination of sawing tool and protective device gives the opportunity to saw along a perpendicular path with one hand very well, with the possibility to hold the object to be sawed in the other hand. Also the tool can be put away safely without the saw disc contacting anything.

Claims: Saw disc (1) with saw teeth (2) spaced around an outer circumference thereof, which form part thereof or are separate saw teeth (2) permanently connected thereto, each of said saw teeth (2) having a cutting edge (5) formed by an adjacent radial flank (8) and an adjacent tangential flank, characterized in that, the tangential flank defines a circular arc (7) and forms a clearance angle (b) with a path of movement of the cutting edge (5) about a centre (A) of the disc (1), wherein a distance between a centre (B) of the circular arc (7) and the centre (A) of the disc ranges from 0,06 to 0,3 times a distance from the cutting edge (5) to the centre (A) of the disc, the centre (B) of the circular arc (7) being located beside a bisector of a portion of the disc (1) bounded by radii of the disc (1) taken at two successive cutting edges (5). Saw disc according to claim 1, characterized in that , the radial flank (8) at its outer end inclines forward in the direction of rotation. Saw disc according to claims 1-2, characterized in that , the radial flank (8) inclines forward at the cutting edge (5) at an angle (a) between -5° and +15°. Saw disc according to claims 1-3, characterized in that , the tangential flank has a clearance angle (b) relative to the path of movement of the cutting edge (5). Saw disc according to claim 4, characterized in that, the clearance angle (b) lies between 2° and 5°. Saw disc according to claims 1-5, characterized in that, the number of teeth (2) is less then ten. Saw disc according to claim 6, characterized in that , the number of teeth (2) is four. Saw disc according to claims 1-7, characterized in that, the teeth (2) have a greater thickness perpendicular to the disc (1) at their cutting edge (5) than the remaining part of the circumference of the disc (1), which greater thickness diminishes gradually behind the cutting edge (5) to the thickness of the remaining part of the circumference of the disc (1). Saw disc according to claim 8, characterized in that , the angular distance, over which a tooth (2) has a greater thickness than the remaining part of the circumference of the disc (1), is about 10° to 20°. Saw disc according to claim 1-7, characterized in that, the teeth (2) and the remaining part of the circumference of the disc (1) have the same thickness and that the teeth (2) are offset alternately in opposite direction from the plane of the disc (1). Saw disc according to claim 10, characterized in that, the set of the teeth (2) is about 0.1 -1.0 mm. Saw disc according to one of claims 1-11, characterized in that , the disc (1) has a maximum thickness of 1.0 to 3.0 mm at the circumference. Saw disc according to claim 1-12, characterized in that, the disc (1) has such a hardness that it can only just be filed, and is made of abrasion or rust resistant steel.

Inventors: HAANSCHOTEN JOZEF GIJSBERT, HAANSCHOTEN, JOZEF GIJSBERT
Applicants: HAANSCHOTEN JOSEF GIJSBERT, HAANSCHOTEN, JOZEF GIJSBERT
Application year: 1996
Main classification: B23D45
IPC codes: B27G19, B23D45, B23D61