GB2181693A - Improvements in and relating to power tools - Google Patents

Abstract

A hand-held power saw with a housing (19) from which extends a tapering support (22) for a saw blade (23) reciprocable along the lower edge of the support by a motor (17) located in the housing (19). The motor (17) is coupled to the saw blade (23) via a driving mechanism incorporating a counterbalance device (12, 14) for counterbalancing the linear out-of-balance forces created by reciprocation of the saw blade (23) and its driving mechanism. <IMAGE>

Description

SPECIFICATION Improvements in and relating to power tools This invention relates to power tools and has particular reference to those having a tool piece that is reciprocated by a driving motorforming part ofthe tool. Examples of such tools are jig-saws and power saws.

In orderto minimise vibration that occurs in those tools whilst they are being used, it is known to counterbalance the mass of moving components.

Previous proposals for counterbalancing such tools have not been entirely satisfactory because they do not provide a completely adequate compensation and because they have resulted in an increase in the size and complexity ofthe tool to accommodate the mechanism for producing the counterbalance and the drive therefor.

According to one aspect, the present invention provides a powertool having a reciprocabletool piece holder, a driving mechanism including a driving memberfor reciprocating the tool piece holder, and a counterbalance device driven bythe mechanism for compensating linear out-of-balance forces set up, when in use, by the member, the holder and a tool piece therein, and in which the driving member and the counterbalance device are so arranged that their centres of gravity move in closely adjacent parallel planes.

The counterbalance device may comprise spaced masses that extend towards the driving member.

The movement of the counterbalance device may be guided bythe driving member.

According to another aspect, the present invention provides a powertool having a reciprocable tool piece holder, a driving mechanism including a driving member for reciprocating the tool piece holder, and a counterbalance device driven bythe mechanism for compensating linear out-of-balance forces set up, when in use, by the member, the holder and a tool piece therein, and in which the counterbalance device comprises spaced masses that extend towards the drive member.

The movement ofthe counterbalance device may be guided bythe driving member.

According to a further aspect, the present invention provides a powertool having a reciprocable tool piece holder, a driving mechanism including a drive member for reciprocating the tool piece holder, and a reciprocable counterbalance device reciprocated by the drive mechanism for compensating out-of-balance forces set up, when in use, by the member, the tool piece holder and a tool piece therein, and in which the reciprocatory movement of the counterbalance device is guided by the member.

The counterbalance device may comprise spaced means.

According to a yetfurther aspect, the present invention provides a powertool having a reciprocabletool piece holder, a driving mechanism including a drive member for reciprocating the tool piece holder, and a counterbalance device driven by the mechanism for compensating linear out-of-balance forces set up, when in use, bythe member,thetool piece holder and atool piece therein, and in which the member and the counterbalance device are nested one with the other in a manner such that their centres of gravity move in closely adjacent parallel planes.

The present invention also provides a power saw tool comprising a housing, a saw blade support extending away from the housing, a driving mechanism located in the housing, the mechanism including a drive member carrying a saw blade clamp for reciprocating a saw blade to and fro along the support, and a counterbalance device driven by the mechanism for compensating linear out-of-balance forces set up, when in use, by the drive member, the clamp and a saw blade carried thereby.

The spaced masses may each be in nesting relationship with the driving member.

The counterbalance device may have a surface or surfaces which coact with a part or parts ofthe driving memberto guide the movementofthe counterbalance device.

Each mass may have a recess in which a part ofthe driving member locates in a manner such that the movement of the counterbalance device is guided by the driving member.

The driving mechanism may be operatively connected to the counterbalance at a location between the spaced masses.

The counterbalance device may have a central portion from which the spaced masses extend, the driving member having two elongate end portions each of which locates in a recess in one ofthe spaced masses.

The driving mechanism may comprise a rotary balanced driving mechanism.

The driving mechanism may include a component located in a transverse slot in the driving member, and a further component located in a transverse slot in the counterbalance device.

The saw blade support may comprise surfacesfor guiding and supporting a saw blade during movement thereof and in which additional bearing means may be provided for supporting the saw blade.

The additional bearing means may be accommodated in the saw blade support.

The additional bearing means may be located ator adjacentthatend of the saw blade support remote from the housing.

The additional bearing means may include a bearing disc.

The disc may be housed in a cut-away in the saw blade support.

The disc may be carried by a spindle whose ends are located in slots in the saw blade support or in a saw blade mounted upon the support.

By way example only embodiments ofthe several aspects of the invention will now be described in greater detail with reference to the accompanying drawings of which: Figure 1 is an underneath view of a part of a drive mechanism incorporating the invention according to one aspect, Figure2 is an end view in schematic form and partly in section of the drive mechanism, Figure3is a section on the line Ill-Ill of Figure 2with some components omitted, Figure 4 is a side view of a power saw embodying the invention according to another aspect, Figure 5is a side view of the saw of Figure 4 with a housing part removed, Figure 6 is a perspective view of a clamp, Figure 7is a perspective view of part of a saw blade assembly and a support, Figure 8 is a side view of a saw blade assembly, Figure 9 is a view of a saw blade assembly in the direction of arrowA in Figure 8, and Figure 10 is a side view on a larger scale of part of the saw blade assembly.

According to one aspect of the present invention, there is provided a powertool having a reciprocable tool piece holder, a driving mechanism including a member for reciprocating the holder, a counterbalance driven bythe mechanism for compensating linear out of balance forces set up, when in use, by the member,thetool piece holder and a tool piece therein, and in which the member and the counterbalance are so arranged that their centres of gravity move in closely adjacent parallel planes.

The mechanism shown in Figures 1,2 and 3forms partofadriveforreciprocatinga linear drive member 1 carrying atool holdertowhich atool piece, for example a saw blade, is attached.

The member 1 has straight end portions 1a between which is formed a transverse enlargement 2 with a slot3 also transverse to the length ofthe member 1.

The member 1 is mounted for reciprocatory movement in bearings indicated diagrammatically at 4 in Figures 1 and 3.

Located in slot3 is a roller5 carried by a stub axis 6 secured at a position offset from the rotational axis 8 of a rotary drive member7.

Themember7 hasa lower disc-like component9 that carries the stub axle 6 and an upperdisc-like component 10 also disposed eccentrically with respect to axis 8. The correct eccentric orientation of the disc-like components 9 and 10 also results in the static balancing of the axle 6 and member 7 carried thereby.

There remains, however, a degree of linear out-of-balance due to the reciprocation ofthe driving member 1 and the tool piece driven thereby. The linear out-of-balance is compensated byforcesset up by a counterbalance device that is reciprocated in anti-phase with respect to the driving member.

The counterbalance device 12 is driven by component 10 via a transverse slot 11 in the device 12. The device 12 comprises a rectangular portion 13 with transverse depending masses 14 at each end thereof.

The weights 14 are both slotted centrally as indicated at 15 in Figure 2 and extend towards the reciprocating member 1 which nests in the slots 15 with a working clearance.

The member 7 is rotated by any suitable mechanism and in Figure 2 is shown a driving gear wheel 16that is secured to or is part of the member7 and is rotated by a gear on the output shaft of a driving motor indicated diagrammatically at 17 in Figure 2.

The bearings 4 are supported in a base member 18 shown in Figure 1.

Thus, as gear wheel 16 is rotated, member 1 is reciprocated bythe action ofthe rotation ofthe lower disc-like component 9 in conjunction with the eccentrically positioned roller 5 and the slot 3.

At the same time, the counterbalance device 12 is also reciprocated bythe action ofthe rotation ofthe upper disc-like component 10in conjunction with the transverse slot in the rectangular portion 13.

The reciprocatory movements ofthe member 1 and the counterbalance device 12 are 1800 out of phase. The physical dimensions of the device 12 and the distribution of its mass (mainly concentrated in the masses 14) are chosen in a manner such that the linear out-of-balance forces created by the member 1,thetool holderandthetool piece aresubtantially offset by the linear out-of-balance forces created by the counterbalance device 12 and its drive.

There is thus provided counterbalancing not only of the out-of-balance forces produced during the rotation of driving member 7 but also of linear out-of-balance forces set up by the reciprocation of the linear drive member 1 and the work piece driven thereby.

It will be appreciated that the arrangement ofthe masses 14which extend towards the drive member 1 enables the planes in which the centres of gravity of the counterbalance device 12 and the drive member 1 reciprocateto be closely adjacent. This reducesthe imbalance couple and the consequential vibration of the tool when in use.

The nesting ofthe drive memberwiththe counterbalance device resulting from the location of the former in recesses in the latter reduces still furtherthespace between the planes just referred to.

At the same time, the recesses provide guide surfaceswhich co-operatewiththestraightend portions 1 a of the drive member 1 toguidethe counterbalance device 12 as it reciprocates- a cost effective arrangement. As has been explained above, the member 1 is itself mounted for reciprocatory movement in the bearings 4which control that movement closely.

The spacing of the masses 14 provides adequate clearance forthe eccentric drive to the counterbalance device.

The mechanism just described may be part of any tool incorporating a reciprocating drive, for example a jig-saw, hedge trimmer, but it can also be employed as part of the driving mechanism forthe blade of a power saw as will now be described in more detail.

The saw is a hand-held tool which embodies another aspect of the present invention is shown in side elevation in Figure 5 and comprises a housing 19 which may be of the so-called clam shell construction. The housing 19 is formed to accommodate the driving motor 17 and to provide a forward knob-like handle 20 and a rear handle grip 21. Extending forwardly from the housing 19 is tapering support 22 along whose lower edge moves a saw blade assembly 23 connected at one end within the housing 19 to the member 1 referred to above.

The motor 17 is energised via a power lead 24from a suitable power source, energisation being controlled by a switch (notshown) actuable bya trigger 25.

Figure 5 showstheway inwhichthe support 22 is held in position. At its wider end, the support 22 has three spaced holes 26 in which locate pins 27 pressed into recesses in the clam shell half 28.

Seated upon internal ribs (not shown) formed on the internal surface oftheclam shell half 28 isthe electric motor 17 whose rotor shaft 30 extends downwardly into a housing that may be formed integ rally with the clam shells and that is indicated diagrammatically at 31. The lower end ofthe rotor shaft 30 is supported by a bearing 32 held in a support member33.

Formed on the extreme lower end of the rotor shaft 30 is a pinion 34that is meshed with the gearwheel 16 of the driving mechanism described above and which is rotatably mounted upon a shaft 36 secured, at its upper end, to the part 33. As described above, the gearwheel 16 has secured to it, or formed integrally therewith, the driving member 7 whose components 9 and 10 impartreciprocatory movement to the counterbalance shaft 12 and the member 1 respectively. The bearings 4 supporting the member 1 for reciprocatory movement are located in the base member 18 seated in the housing 31.

The forward end of the member 1 projects from the housing 31 beneath the support 22 where it is detachably secured to a reduced end portion 47 of the saw blade assembly 23 by a clamp 39 shown in more detail in Figure 6.

The clamp 39 is of generally cubic form with a slot 40forthe reception ofthe reduced end width portion 47 of the assembly 23. The clamp has a threaded hole 41 transverse to the slot 40 forthe reception of a screw (not shown) which grips and holds the end portion 47 in the slot. Access to the securing screw is permitted via a slot 41 a in the housing of the saw thereby enabling a user readily to remove and attach a blade assembly. Furtherfixing holes 42 on the upperface of the clamp enable the latterto be secured to the forward end ofthe member 1 by screws which pass through the latter and into the holes 42. Other methods of fixing the blade assembly to the drive member 1 may be used instead.

The saw blade assembly shown in Figures 7-9 comprises a laminated structure formed of two outer strips 43,44 formed with teeth 45,46 respectively along their lower (as viewed in Figure 7) edges. The right-hand (as viewed in Figure 7) end portions ofthe strips 43,44 are of a reduced depth as compared with the remainder of the strips and as indicated at47.

There are no teeth along the lower edge ofthe reduced depth portions.

The outer strips 43,44 are separated by an inner strip 48 whose depth is considerably less than that of the major parts of the strips 43,44 and slightly less than the depth ofthe portions 47. The inner strip 48 is so located that its lower edge (as seen in Figures 8 and 9) is level with the roots of the teeth 45,46 thus forming a longitudinal gap 49 between the upper parts ofthe strips 43,44.

There is thus formed a saw blade assembly in which the roots of the teeth 45,46 are spaced from one another laterally by a gap equal to thethickness of the inner strip 48.

The teeth 45,46 are oftriangularform when seen in side elevation as in Figures 8 and 10 ofthetriangles forming the roots of the teeth. The teeth are arranged in pairs on each strip and the sloping edges are bevelled on their facing sides as indicated at 50to form points at the tips of the teeth. Thus, the extreme left-hand tooth 51 shown in Figure 10 is the first of the teeth 46 and is bevelled on its inside face. The next tooth 52 is the first of the teeth 45 and is bevelled on its outside face, the next tooth 53 is the second ofthe teeth 45 and is bevelled on its inside face. The next tooth 54 is second ofthe teeth 46 and is bevelled on its inside face whilst the next tooth 55 is the third of the teeth 46 and soon.The bevels tapertowardsthe edges of the teeth as can be seen from Figure 10.

Pairs of teeth on one strip locate centrally of the space between pairs of teeth on the other strip,the teeth being equi-spaced along the length of the assembly. That is to say,thedistance between each pair of teeth is greater than that between the teeth of a pair.

Alternate ones of the teeth 45 are set outwardly as indicated at 46 in Figure 9 whilst the others are set inwardly as indicated at 57. In similar manner, alternate teeth of teeth 46 are also set outwardly as indicated at 58 in Figure 8, the remaining teeth being set inwardly as indicated at 59. Thus, in each pair of teeth, one tooth is bevelled on its inside face and set outwardly while the other tooth of the pair is bevelled on its outside face and set inwardly. The outward sets are sufficient to ensure that the tooth points lie externally of the faces of the other strips 43,44 as can be seen from Figure 8 and externally of the faces of a supportaswill be described below.This allowsfor the clearance of saw dust produced during sawing and reduces friction between the faces of the blade assemblyandthefaces of the saw cut.

In one form of blade assembly shown in Figures 8, 9 and 10, the strips 43, 44 are of a thickness of about 0.7 mm and of a depth, as measured from the upper edge to the tooth points, of about 20 mm. The depth of each tooth as measured from root to point is about 5.0 mm. The depth oftheslot7 is about 6.0 mm.

The pitch of the teeth 45,46 is about 24.00 mm. The first tooth oftheteeth 45 lies at the left-hand end of strip 43 while the firsttooth of teeth 46 is spaced from the left-hand end of strip 44to givethetooth locations referred to above. At the other ends ofthe strips 43,44, the extreme right-hand tooth is one of teeth 46. The included tip angle at the tooth point is about 42".

The distance between adjacent teeth when the assembly is viewed from the side is about 6.0 mm.

The tooth configuration of the assembly shown in Figures 8,9 and 10 is suitableforgeneral wood-cutting operations in timber and may also be used to cut other materials.

Attheforward end ofthe saw blade, a disc 60 is shown rotatably mounted upon a spindle 61. The spindle is supported, at its ends, in slots 62 in the blades 43, 44 and is free to roll along the upper edge ofthe inner strip 48 within limits set by the length of the slot. Those limits are set by the stroke of the blade assembly and must be sufficient to accommodate the stroke.

It is not essential to mount the disc 60 on a spindle, it could be loose. In that case, the slots 62 are not required.

The spindle could alternatively be supported in slots in the support 22.

The disc 60 is also in contact with the upper edge 63 of a cut-away 64 in the support22.

The presence ofthe disc 60 reduces friction between the wearing faces ofthe inner strip 48 and the blade support 22.

The physical size and mass distribution ofthe counterbalance shaft 12 are chosen to compensate substantially completely for the linear out-of-balance forces produced bythe member 1 and the saw blade assembly 23 and thereby to minimise the overall vibration of the tool whilst in use. The tool is therefor more comfortable to use.

The reciprocatory movements of shaft 12 and member 1 are 1800 out-of-phase due to the relative positions ofthe pin 6 and the upper disc portion 10 relative to the rotational axis 8.

It will be appreciated that other forms of saw blade than the composite assembly described above can be used. A blade with a single row of teeth and suitably contoured to coact with a blade support and guide can be used instead. Such a blade is referred to herein as a blade assembly. Examples of other suitable blades and blade assemblies and supports therefore are found in U.K. PatentApplications Nos.

85.16809and85.16810.

The invention may also be embodied in bench mounted, i.e. stationarytools,and is not limited to hand-held tools. The power saw described above may be bench-mounted either on a mounting that enables itto be brought down on to a work piece or in a manner enabling a work piece to be offered upto the blade.

Claims (24)

1. A powertool having a reciprocable tool piece holder, a driving mechanism including a driving member for reciprocating the tool piece holder, and a counterbalance device driven by the mechanism for compensating linear out-of-balance forces set up, when in use, by the member, the holder and a tool piece therein, and in which the driving member and the counterbalance device are so arranged that their centres of gravity move in closely adjacent parallel planes.

2. A powertool having a reciprocable tool piece holder, a driving mechanism including a driving memberfor reciprocating the tool piece holder, and a counterbalance device driven bythe mechanism for compensating linear out-of-balance forces set up, when in use, bythe member, the holder and a tool piece therein, and in which the counterbalance device comprises spaced masses that extend towards the drive member.

3. A powertool having a reciprocable tool piece holder, a driving mechanism including a drive member for reciprocating the tool piece holder, and a reciprocable counterbalance device reciprocated by the drive mechanism for compensating out-of-balance forces set up, when in use, by the member,thetool piece holder and atool piece therein, and in which the reciprocatory movement of the counterbalance device is guided by the member.

4. A powertool having a reciprocabietool piece holder, a driving mechanism including a drive member for reciprocating the tool piece holder, and a counterbalance device driven bythe mechanism for compensating linear out-of-balance forces set up, when in use, by the member, the tool piece holder and a tool piecetherein, and in which the member and the counterbalance device are nested one with the other in a manner such that their centres of gravity move in closely adjacent parallel planes.

5. A power saw tool comprising a housing, a saw blade support extending away from the housing, a driving mechanism located in the housing, the mechanism including a drive member carrying a saw blade clamp for reciprocating a saw blade to and fro along the support, and a counterbalance device driven by the mechanism for compensating linear out-of-balance forces set up, when in use, by the drive member, the clamp and a saw blade carried thereby.

6. Atool as claimed in claim 1,3, 4or5 in which the counterbalance device comprises spaced masses that extend towards the driving member.

7. Atool as claimed in claim 1,2, 4or5 in which movement of the counterbalance device is guided by the driving member.

8. Atool as claimed in claim 1,4 or 5 in which the counterbalance device comprises spaced masses that extend towards the driving member and in which movement of the counterbalance device is guided bythe driving member.

9. Atool as claimed in claim 2,6 or 8 in which the spaced masses are each in nesting relationship with the driving member.

10. Atool as claimed in claim 3,7 or8 in which the counterbalance device has a surface or surfaces whichcoactwitha part or parts of the driving memberto guide the movementofthe counterbalance device.

11. Atool as claimed in claim 2,6,8,9 or 10 in which each mass is provided or formed with a recess in which a part of the driving member locates in a manner such thatthe movement of the counterbalance device is guided by the driving member.

12. Atool as claimed in claim 2,6,8,9,10 or 11 in which the driving mechanism is operatively connected to the counterbalance at a location between the spaced masses.

13. Atool as claimed in claim 11 or when appended to claim 11 in which the counterbalance device has a central portion from which the spaced masses extend and in which the driving member has two elongate end portions each of which locates in a recess in one of the spaced masses.

14. Atool as claimed in any one ofthe preceding claims in which the driving mechanism comprises a rotary balanced driving mechanism.

15. Atool as claimed in claim 14 in which the driving mechanism includes a component located in a transverse slot in the driving member, and a further component located in a transverse slot in the counterbalance device.

16. Atool as claimed in claim 5 or any one of claims 6-15 when appended to claim Sin which the saw blade support comprises surfaces for guiding and supporting a saw blade during movement thereof and in which additional bearing means are provided for supporting the saw blade.

17. Atool as claimed in claim 16 in which the additional bearing means are accommodated in the saw blade support.

18. Atool as claimed in claim 16 or 17 in which the additional bearing means are located at or adjacent that end of the saw blade support remote from the housing.

19. Atool as claimed in claim 16,17 or 18 in which the additional bearing means includes a bearing disc.

20. Atool as claimed in claim 19 in which the disc is housed in a cut-away in the saw blade support.

21. Atool as claimed in claim 20 in which the disc is carried by a spindle whose ends are located in slots in the saw blade support.

22. Atool as claimed in claim 19,20 or 21 in combination with a saw blade mounted upon the saw blade support and in which the saw blade has slots in which are located the ends of a spindle upon which the disc is mounted.

23. A power tool substantially as herein described with reference to and as illustrated by Figures 1-3 of the accompanying drawings.

24. A power saw substantially as herein described with reference to and as illustrated bythe accompanying drawings.