AU2012342663A1 - Improved bow saw frame and corresponding bow saw - Google Patents

Abstract

The invention relates to a frame comprising a bow that is solidly connected to a rear handle (4), front and rear hook members, and a mechanism for tensioning a saw blade (2) when the blade is hooked to the front and rear hook members. The aforementioned mechanism comprises a rotary control member (34) coupled to a screw-and-nut system (52, 68), and a disengageable rotary device (32) positioned between the control member (34) and the nut-and-screw system (52, 68), said device limiting the torque transmitted from the control member (34) to the nut-and-screw system (52, 68). The invention is suitable for a bow saw.

Description

1 IMPROVED BOW SAW FRAME AND CORRESPONDING BOW SAW The present invention relates to a bow saw frame of the type that comprises a bow rigidly connected to a rear handle; a front locking device connected to the bow 5 and designed to lock the distal end of a saw blade, the front device being provided at the front end of the frame; a rear locking device connected to the handle and designed to lock the proximal end of the saw blade, the rear device being provided at the rear end of the frame; a tensioning mechanism for the saw blade when said blade is locked to the front and rear locking devices, the mechanism comprising a rotating 10 control component coupled to a screw and nut system. Document FR-A-2 702 167 shows an example of this type of saw frame. However, this type of frame cannot prevent the risk of over-tensioning the blade which could lead to the partial destruction of the frame. The object the invention is to provide economical and reliable means for 15 easily applying precise tension to the blade without the risk of damaging the frame. Accordingly, the invention relates to a saw frame of the above-mentioned type, in which the tensioning mechanism comprises a disengageable rotary device, positioned between the control component and the screw and nut system. The saw frame according to the invention may comprise one or more of the following 20 characteristics: - the torque-limiting device is incorporated in the control component to form a sub-unit; - the torque-limiting device decouples the control component from the screw and nut system, which is connected to the rear locking device, when the control 25 component is actuated in the direction of rotation that corresponds to the tensioning of the blade and a threshold torque value has been reached; - the torque-limiting device acts in such a way that the control component remains coupled to the screw and nut system when the control component is actuated in the direction of rotation that corresponds to the release of tension of the 30 blade; - the torque-limiting device comprises two toothed rings with complementary gear teeth in mutual axial engagement and a stress component that acts to mutually engage said toothed rings; P-EP-IAR1028#NOV 2 - the gear teeth are asymmetrical, each tooth comprising a first sloping side face and a second straight side face delimiting a third substantially straight transverse face; - the control component is a crank made of a moulded plastics material 5 comprising a housing that receives at least in part the torque-limiting device which is covered by a cap made of a moulded plastics material welded to the crank; - the handle comprises a lower recess in which the control component is housed by matching of forms; - the bow and the rear handle are produced in a single piece, in particular of 10 moulded aluminium. The invention also relates to a bow saw comprising a saw frame as described above, and at least one saw blade suitable for being locked in said front and rear locking devices. An embodiment of the invention will now be described in relation to the 15 accompanying drawings, in which: - Fig. 1 is a view in elevation of a bow saw according to the invention; - Fig. 2 is an exploded perspective view of the saw of Fig. 1; - Fig. 3A is a perspective view of the means for adjusting the tension of the saw blade; 20 - Fig. 3B is an exploded perspective view of the adjustment means of Fig. 3A; - Fig. 3C is an enlarged diagrammatic view in elevation of the gear teeth profile present in the adjustment means of Fig. 3A; - Fig. 4 is an enlarged view of detail IV of Fig. 1 of the rear portion of the saw with partial cut-out; 25 - Fig. 5A and 5B are views showing the operation of the means for adjusting the tension of the saw blade of Fig. 3A. The bow saw illustrated in Fig. 1 and 2 comprises a frame 1 which carries a saw blade 2. The frame 1 comprises a bow 3 which is rigidly connected to a rear handle 4. It also comprises a front locking device 5 and a rear locking device 6. The 30 blade is locked to the devices 5 and 6 and tensioned by means of a tensioning mechanism 7 incorporated in the handle. It will be assumed that the frame is oriented as shown, with the blade at the bottom. The bow 3 consists of a single piece. It is generally L-shaped, with a front branch 8 that slopes slightly forwards and downwards by about 180, and an upper P-EP-IAR1028#NOV 3 branch 9 which is substantially horizontal, the rear end of which is integral with the upper portion 10 of the handle in the extension thereof. The upper portion 10 of the handle is substantially horizontal. The handle 4 comprises a front beam 11 and a rear portion 12 that can be 5 easily grasped by an operator, the front beam and the rear gripping portion being substantially parallel and having the same rearward and downward slope of about 140. The front beam 11 is connected integrally with the upper portion 10 of the handle. The handle also comprises a lower portion 13 that is substantially horizontal and connects the lower ends of the front beam 11 and the rear gripping portion 12. 10 The lower portion 13 contains the tensioning mechanism 7. The lower end 14 of the front branch 8 comprises a graduated bore 15 that extends along a longitudinal axis X-X oriented from back to front. The bore 15 comprises a first guide piece of circular cross-section (not illustrated) opening on the blade 2 side and a second piece that is also of circular cross-section (also not 15 illustrated) with a diameter greater than that of the guide piece. The second piece opens, opposite the blade 2, on a face comprising a plurality of recesses 16 arranged at regular angles. The front locking device 5 comprises an intermediate shank 17 of circular cross-section delimited by a locking portion 18 of the blade 2 and a head 19, the unit 20 being produced as one piece of metal. In an alternative embodiment (not illustrated), a front locking device comprising a steel shaft and a head made of a plastics material which are separate and are assembled by a metal pin may be envisaged. The head 19 comprises a plurality of indexing bosses 20, in particular four bosses arranged at regular angles, suitable for cooperating with some of the plurality of recesses 16 in 25 order to orient the front locking device 5 at an angle to the frame 1. The diameter of the first guide piece corresponds, allowing for play, to that of the intermediate shank and allows said shank to be guided sliding. The second portion of the bore 15 receives a spiral compression spring 21, one end of which rests against the shoulder of the bore 15 and the other end of 30 which rests against the head 19. The spring 21 is suitable for surrounding the intermediate shank 17. The front locking device 5, loaded by the spring 21, is mounted sliding in the bore 15. A pin 22 is inserted using force into a traversing boring 23 positioned cross wise relative to the intermediate shank 17 on the blade side. The pin 22 limits the P-EP-IAR1028#NOV 4 sliding travel of the front locking device 5. Said front locking device acts on the distal end of the blade 2 so as to move it towards the front branch 8. The lower portion 13 of the handle 4 comprises a stepped bore 24 that extends along a longitudinal axis X'-X' oriented from back to front. The axes X-X and 5 X'-X' are substantially aligned. In Fig. 4, on the blade 2 side, the bore 24 comprises a first piece 25, which is slightly conical from front to rear and of circular cross-section. The piece 25 comprises two longitudinal ribs 26a and 26b (only the groove 26b is shown in Fig. 2) arranged projecting radially inside and diametrically opposite. Said ribs converge along the axis X'-X' to a point positioned opposite the blade 2 relative 10 to the lower portion 13. The first piece 25 extends over about two thirds of the length of the bore 24. The piece 25 extends axially from a second piece 27 of circular cross-section, the diameter of which is less than that of the first piece 25. The second piece 27 extends over about one third of the length of the bore 24. 15 A third piece 28 of circular cross-section and with a diameter that is less than that of the second piece 27 extends said second piece axially opposite the blade 2. The piece 28 extends over a shorter length. In Fig. 4, on the side of the lower portion 13 opposite the blade 2, the third piece 28 of the bore 24 opens into a first counterbore 29 of circular cross-section with 20 a diameter that is less than that of the piece 25 and greater than that of the piece 27, which is extended by a second bore 30 of circular cross-section, the diameter of which is greater than that of the piece 25. The second counterbore 30 opens into a recess 31 produced in the lower portion of the grasping branch 12 of the handle 4. The recess 31 comprises a flat 25 surface contained in a plane perpendicular to the axis X'-X'. This flat surface is extended upwards by an overhanging concave round corner. The first and second counterbores 29 and 30 extend along the axis X'-X' and form a housing in which the front portion 33 of a torque-limiting device 32 (Fig. 2) is received, said front portion extending along the axis X'-X' projecting from a control 30 component or crank 34, which is moulded in a plastics material, for example. The torque-limiting device 32 is incorporated in the crank 34 to form a sub unit, the operation of which will be described later. In Fig. 3A and 3B, the crank 34 is shaped like a shell which is open at the front, with a dividing wall of reduced thickness. This shell has a shape that matches P-EP-IAR1028#NOV 5 that of the recess 31 in the lower portion of the handle 4 so as to complete said handle when the crank 34 is in place in said recess. The crank 34 comprises an arc-shaped upper rib 35, which extends from one edge to the other of the lateral sides 36 and 37 of the shell and terminates slightly set 5 back relative to the plane of said edges. The lower portion of the shell forming the crank 34 comprises an arc-shaped lower rib 38, which extends from one edge to the other of the lateral sides 36 and 37 of the shell and terminates in the plane of said edges. The lower rib 38 and a neck 38a (Fig. 3B) delimit a blind cylindrical housing 10 39, which extends along the axis X'-X'. On its inner periphery, it comprises a plurality of ribs 40 and grooves 41 arranged projecting alternately and radially, and extending along the axis X'-X'. The housing 39 is suitable for receiving a drive bush 42 with an indented outer profile 42a of a shape that matches that of the profile of the housing 39. A stress component 43, in particular a spiral compression spring, one end of 15 which rests on the bottom of the housing 39, loads the bush 42 axially. In Fig. 4, the bush 42 comprises a counterbore 44 that opens on the housing 39 side of the crank 34, in the bottom of which the other end of the spring 43 rests. The bush is mounted moveably sliding along the axis X'-X' relative to the housing 39. The spring 43 tends to maintain the bush 42 projecting slightly relative to the housing 20 39. The front face 45 of the bush 42 comprises a toothed ring 46, the teeth of which extend radially perpendicular to the axis X'-X' and the transverse profile of which is asymmetrical. Two adjacent teeth are separated by a recess of complementary shape. 25 In Fig. 3C, each tooth of the ring 46 comprises a first side face 46a that slopes relative to the axis X'-X' and a second straight side face 46b that is substantially parallel to the axis X'-X' delimiting a third straight transverse face 46c that is substantially perpendicular to the axis X'-X'. The front face 45 also comprises a boring 47 (Fig. 3B) that opens into the 30 counterbore 44. The torque-limiting device 32 also comprises a hollow driven shaft 48 comprising an intermediate collar 49 provided with a toothed ring 50 of a shape that matches that of the drive bush 42. P-EP-IAR1028#NOV 6 The rings 46 and 50 have complementary gear teeth that engage with each other axially. In Fig. 3C, each tooth of the ring 50 comprises a first side face 50a that slopes relative to the axis X'-X' and a second straight side face 50b that is substantially parallel to the axis X'-X' delimiting a third straight transverse face 50c 5 that is substantially perpendicular to the axis X'-X'. The compression spring 43 acts so as to mutually engage the toothed rings 46 and 50. The collar 49 is delimited at the front by a cylindrical shank 51 that receives a cylindrical insert 52 with a tapped bore 53 (Fig. 3B and 4) and, at the rear, by a sleeve 54 that has an axial transverse boring 55 (Fig. 4) that opens into a tapped 10 bore 53 of the insert 52. Said insert corresponds to the female portion of a screw and nut system. The collar 49, the shank 51 and the sleeve 54 consist of a single piece, made for example of a plastics material, whereas the insert 52 is metal. The torque-limiting device 32 is covered by a cap 55 (Fig. 3B), made of a 15 plastics material, for example, and comprises a bore that has two different diameters (Fig. 4). The rear piece 56 has a large diameter and covers the toothed rings 46 and 50. The front piece 57 has a smaller diameter and receives the shank 51 of the shaft 48. The rear free end 58 of the cap engages with the neck 38a of the crank 34 to which the cap is rigidly connected. 20 Preferably, the plastics material of the crank 34 and of the cap 55 are compatible to allow the two parts to be welded. This assembly results in a very economical cost for the sub-unit. In this sub-unit configuration, the front portion of the shank 51 of the torque limiting device 32 projects slightly axially relative to the cap 55 (Fig. 3B). 25 Under the action of the spring 43, the toothed rings 46 and 50 are mutually engaged, the collar 49 of the shaft 48 resting on the inner shoulder 59 (Fig. 3B) of the cap 55. The drive bush 42 is rigidly connected to the crank 34 rotating relative to the axis X'-X' and is moveable sliding along the same axis relative to said crank against 30 the action of the spring 43. In Fig. 2 and 4, the rear locking device 6 extends along the axis X'-X' and comprises from front to back a locking portion 60 for the blade 2 extended by a slider 61 of square cross-section, which is itself connected to a cylindrical guide piece 62 of circular cross-section by means of a connecting piece 63, a collar 64 extending P-EP-IAR1028#NOV 7 radially at the periphery of the guide piece 62. The collar is connected to a cylindrical support piece 65 of circular cross-section having a diameter that is less than that of the collar and is suitable for supporting on its outer periphery, allowing for play, the inside of the coils of a spiral compression spring 66, one end of which rests on the 5 collar. The locking device 6 also comprises a rear rod 67 which is integral with the piece 65, and of which the free threaded end 68 is suitable for cooperating with the tapped bore 53 of the insert 52 of the drive bush 42. The diameters of the rear rod 67 and of the threaded end 68 are slightly less than that of the piece 28 of the bore 24 so as to pass therethrough. The threaded rod 68 corresponds to the male portion of a 10 screw and nut system. The rear locking device 6 is produced preferably in a single piece in metal, such as steel. To assemble the locking device 6 in the handle 4, the operator threads the spring 66 onto the rod 67 and positions it so that it surrounds the support piece 65 allowing for play. The device 6 is then mounted in the bore 24 of the lower portion 13 15 of the handle so that the threaded rod 68 passes through the piece 28 and opens into the counterbores 29 and 30. The spring 66 rests, on the one hand, against the straight shoulder separating the collar 64 and the piece 65 and, on the other hand, against the straight shoulder separating the pieces 27 and 28 of the bore 24. 20 A conical maintenance sleeve 70 (Fig. 2 and 4) of circular cross-section comprises two diametrically opposite grooves 71a and 71b suitable for cooperating with the grooves 26a and 26b respectively of the piece 25. It also comprises a front orifice 72 of non-circular cross-section, in this case of octagonal cross-section, suitable for cooperating with the slider 61 to index the blade 2 at an angle relative to 25 the frame 1. A cylindrical guide bore 74 (Fig. 4) of circular cross-section extends the orifice 72 rearwards. The bore 74 is suitable for the piece 62 to move rotating relative to the axis X'-X' and sliding along said axis inside the sleeve 70. Once the grooves 71a and 71b are engaged with the ribs 26a and 26b respectively, the operator fits the sleeve 70 by force in the bore 24 so that it is rigidly 30 connected to the handle 4. At this stage of assembly, the rear locking device 6 is configured as shown in Fig. 4, that is to say so that the spring 66 pushes the collar 64 to abut against the sleeve 70, so that the slider 61 is not engaged with the octagonal orifice 72 and so that the threaded end 68 of the rod 67 opens into the counterbore 30. P-EP-IAR1028#NOV 8 The operator presents the sub-unit consisting of the torque-limiting device 32 equipped with the cap 55 connected to the crank 34 facing the threaded rod, and engages said sub-unit on the rod by actuating the crank in a rotating movement relative to the axis X'-X' corresponding to a direction of screwing of the sub-unit onto 5 the threaded end 68 of the rod. The slider 61 is moved axially while simultaneously turning with the crank 34 until it abuts the octagonal orifice 72 of the sleeve. The operator selects the orientation of the slider 61 relative to the frame 1 by engaging it in the octagonal orifice 72 by light axial pressure against the action of the spring 66. While maintaining this pressure, he then continues screwing the torque 10 limiting sub-unit 32 with crank 34 onto the threaded rod 68 until the front portion 33 of the torque-limiting sub-unit with crank abuts the bottom of the counterbore 29 (Fig. 4). Once the slider 61 is engaged in the octagonal orifice 72, the operator fixes the saw blade 2 to the locking devices 5 and 6 which are oriented at an angle relative 15 to the frame 1 selected by the operator. It should be noted however that the blade could be mounted before the angle is selected. The user then continues to rotate the crank 34 in the direction of screwing, which quickly leads to the tensioning of the blade 2. As shown in Fig. 5A, when the rotation effort applied by the operator to the 20 crank 34 produces a turning moment C where the sloping faces of the toothed rings 46 and 50 engage, and this produces an axial component that is less than the axial reaction effort of the compression spring 43 shown by the arrow F, said toothed rings remain mutually engaged. The drive bush 42 is held axially in the forward position and the turning moment C is transmitted to the driven shaft 48. Because the threaded 25 rod 68 is coupled to the tapped insert 52 of the shaft 48, the turning moment C is converted into a sliding movement from front to back of the threaded rod 68 relative to the axis X'-X'. Tensioning of the blade 2 takes place. As shown in Fig. 5B, when the rotation effort applied by the operator to the crank 34 produces a turning moment C' where the sloping faces of the toothed rings 30 46 and 50 engage, and this produces an axial component that is greater than or equal to the axial reaction effort of the compression spring 43 shown by the arrow F, the sloping faces 46a and 50a of the toothed rings 46 and 50 slide relative to each other, which produces a sliding movement d from front to back of the drive bush 42 against the action of the spring 43. The drive bush 42 is disengaged from the shaft P-EP-IAR1028#NOV 9 48, and is momentarily in the rear axial position. The turning moment C' is not transmitted to the driven shaft 48, which immobilises the threaded rod 68. Tensioning of the blade 2 is halted. The torque-limiting device 32 is a disengageable rotary device positioned 5 between the control component 34 and the screw and nut system comprising the tapped insert 52 and the threaded rod 68. The rings 46 and 50 are kept disengaged as long as the straight transverse faces 46c and 50c of the gear teeth are in contact under the load of the compression spring 43. 10 An additional rotation movement of the crank 34 relative to the axis X'-X' in the direction of screwing allows the toothed rings 46 and 50 to be mutually engaged again. The operator repeats the action until the crank 34 is positioned substantially in the recess 31 of the handle 4, without having increased the tensile load on the 15 blade. Because of the torque-limiting device 32, the tensioning mechanism 7 of a saw blade 2 allows a predetermined tensile load to be applied to the blade that is proportional to the reaction effort of the calibrated spring 43. In operation, the torque-limiting device 32 avoids the application of too great a 20 tensile load on the locking devices 5 and 6 that could lead to the distortion or destruction of the frame 1 or of the tensioning mechanism 7. If the operator wishes to release the tension of the blade 2, for example to replace it, he turns the crank 34 in the direction that corresponds to unscrewing the torque-limiting device 32 relative to the threaded rod 68. 25 The toothed rings 46 and 50 act on each other by means of the straight side faces 46b and 50b that remain mutually engaged whatever the value of the turning moment applied to the drive bush 42 rotating relative to the axis X'-X'. The tension of the blade 2 is released following a plurality of rotational movements of the crank 34, which allows the blade to be removed from the locking 30 devices 5 and 6. The torque-limiting device 32 therefore decouples the control component 34 from the screw and nut system consisting of the insert 52 and the threaded end 68 of the rod 67 when the control component is actuated in the direction of rotation that P-EP-IAR1028#NOV 10 corresponds to the tensioning of the blade and a threshold torque value is reached and applied to the torque-limiting device 32. If the control component is actuated in the direction of rotation that corresponds to the release of the blade tension, the same device 32 acts so that the 5 control component 34 remains coupled to the screw and nut system whatever torque value is applied to said device. Preferably, the bow 3 and the rear handle 4 are made in a single piece, in particular of moulded aluminium. Because of the invention a saw frame is provided with economical and 10 reliable means of easily applying a precise tension to the blade without the risk of damage to the frame. The invention also relates to saw frames that have a curved bow. P-EP-IAR1028#NOV

Claims (10)

1. Bow saw frame of the type that comprises a bow (3) rigidly connected to a rear handle (4); a front locking device (5) connected to the bow and designed to lock 5 the distal end of a saw blade (2), the front device being provided at the front end of the frame; a rear locking device (6) connected to the handle and designed to lock the proximal end of the saw blade, the rear device being provided at the rear end of the frame; a tensioning mechanism (7) for a saw blade when said saw blade is locked to the front (5) and rear (6) locking devices, the mechanism (7) comprising a rotating 10 control component (34) coupled to a screw and nut system (52, 68), characterised in that the tensioning mechanism (7) comprises a disengageable rotary device (32) positioned between the control component (34) and the screw and nut system (52, 68), said device limiting the torque transmitted from the control component (34) to the screw and nut system (52, 68). 15

2. Frame according to claim 1, characterised in that the torque-limiting device (32) is incorporated in the control component (34) to form a sub-unit.

3. Frame according to either claim 1 or claim 2, characterised in that the torque 20 limiting device (32) acts by decoupling the control component (34) from the screw and nut system (52, 68), which is connected to the rear locking device (6), when the control component (34) is actuated in the direction of rotation that corresponds to the tensioning of the blade (2) and a threshold torque value has been reached. 25

4. Frame according to any of claims 1 to 3, characterised in that the torque limiting device (32) acts in such a way that the control component (34) remains coupled to the screw and nut system (52, 68) when the control component (34) is actuated in the direction of rotation that corresponds to the release of tension of the blade (2). 30

5. Frame according to any of claims 1 to 4, characterised in that the torque limiting device (32) comprises two toothed rings (46, 50) with complementary gear teeth in mutual axial engagement and a stress component (43) that acts to mutually engage said toothed rings. P-EP-IAR1028#NOV 12

6. Frame according to claim 5, characterised in that the gear teeth are asymmetrical, each tooth comprising a first sloping side face (46a, 50a) and a second straight side face (46b, 50b) delimiting a third substantially straight transverse 5 face (46c, 50c).

7. Frame according to any of claims 1 to 6, characterised in that the control component (34) is a crank made of a moulded plastics material comprising a housing (39) that receives at least in part the torque-limiting device (32) which is covered by a 10 cap (55) made of a moulded plastics material welded to the crank.

8. Saw frame according to any of claims 1 to 7, characterised in that the handle (4) comprises a lower recess (31) in which the control component (34) is housed by matching of forms. 15

9. Saw frame according to any of claims 1 to 8, characterised in that the bow (3) and the rear handle (4) are produced in a single piece, in particular of moulded aluminium. 20

10. Bow saw, characterised in that it comprises a saw frame (1) according to any of claims 1 to 9, and at least one saw blade (2) suitable for being locked in said front (5) and rear (6) locking devices. P-EP-IAR1028#NOV