Hand-holdable electric reciprocating cutting tool

A hand-held power cutting tool has a generally cylindrical casing, which can be grasped in the palm of one hand, and whose rear portion housed an electric driving motor disposed in the casing with its axis of rotation lying along the longitudinal axis of the rear portion. Reciprocated by the motor via a drive transmission system is a cutter carrier mounted for reciprocatory movement in a bearing support structure. The cutter carrier carries a clamp by which a cutter is attached to the carrier. The carrier is reciprocated at a rate of between 4,000 and 12,000 movements per minute and with a stroke of from 4 to 12 mm for rapid cutting of thin material. The cutter may have a generally U-shaped blade.

FIELD OF THE INVENTION 
This invention relates to power tools and has particular reference to a 
hand-holdable, power tool adapted to operate with a variety of cutting 
blades for cutting a wide range of different materials. 
BACKGROUND OF THE INVENTION 
Applicant has appreciated that the reciprocatory movement imparted to a 
cutter tool should be sufficiently rapid to effect cutting without 
resulting in overheating of the cutting blade and damage to the material 
being cut. Furthermore, applicant has appreciated that the stroke of the 
cutting tool also plays an important part in effective cutting. The stroke 
should be sufficient to ensure cutting and yet not result in excessive 
vibration of the tool particularly when hand-held. 
These conflicting requirements for a hand-held cutting tool have not been 
satisfactorily met in the past. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a hand-holdable power 
reciprocating cutting tool that better satisfies the above requirements, 
particularly a small tool that can be grasped in the palm of one hand such 
as a padsaw. 
Accordingly, therefore, there is provided by the present invention a power 
tool comprising a drive motor coupled by a drive transmission system to a 
cutter carrier characterized in that the motor in conjunction with the 
transmission system is adapted to impart to the carrier a reciprocatory 
motion of a stroke of from 4 to 12 mm and at a rate in the range of 
4,000-12,000 (both limits included) reciprocatory movements per minute. 
Preferably, the stroke lies within the range of from 6-10 mm (both limits 
included). 
The rate may lie within the range of from 7,000 to 12,000 movements (both 
limits included) per minute but preferably is within the range 8,500 to 
10,000 (both limits included). 
In one particular embodiment of the invention, the stroke is 8 mm and the 
rate of reciprocation either 8,500 or 10,000 movements per minute. 
The tool may have a casing of generally cylindrical form sized to allow a 
user to hold and manipulate the tool during use by grasping the casing. 
The casing may accommodate the drive motor which is so orientated that its 
longitudinal axis--the axis of rotation--lies along the longitudinal axis 
of the casing. 
The carrier may be mounted for reciprocatory movement along an axis 
extending in the same direction as the axis of the casing. 
The drive motor may occupy a rear cylindrical portion of the casing whilst 
the transmission system occupies a forward part of the casing. 
The transmission system may comprise a bracket rotatably supporting an 
eccentric by means of which reciprocatory movement is imparted to the 
carrier. 
The bracket may also support a thrust bearing for supporting axial loads 
applied to the eccentric. 
The carrier may be mounted for reciprocatory movement in spaced bearings 
supported by a support structure comprising separable members each with 
spaced support surfaces for supporting the bearings. 
The carrier may be accommodated entirely within the casing and remains so 
during reciprocation of the member. 
The carrier may be aligned with an aperture in the forward face of the 
casing and carries a work piece clamp at that end adjacent the forward 
face. 
The casing may be apertured in the vicinity of the clamp to give access to 
the latter. 
The casing may have a slide movable between a position in which the 
aperture is exposed and another position in which the slide covers the 
aperture. 
In another aspect of the present invention, a power tool has a casing of a 
clam shell construction and includes a first cylindrical portion sized to 
allow it to be grasped and held by a user's hand, and a second portion 
extending from the first portion, the first portion accommodating a drive 
motor assembly with a longitudinal axis lying along the longitudinal axis 
of the first portion, the second portion accommodating a cutter carrier 
mounted for reciprocatory movement in the direction of the longitudinal 
axis of the first portion and accommodating a drive transmission system 
interconnecting the motor and the drive member for imparting reciprocatory 
movement to the latter. 
The drive motor may be an electric motor.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The embodiment is a hand-held, powered cutting tool with a casing 1 of 
elongate generally-cylindrical form. The casing is of a clam shell 
construction comprising body halves 2, 3 of a plastics material. The 
halves have mating edge configurations and are held together by screws 4 
that pass through apertures in one body half and into holes in bosses in 
the other body half. 
The casing 1 has a rear portion 5 of generally cylindrical shape and of a 
diameter that enables this portion to the casing to be readily grasped by 
the hand of a user to use the tool. 
The rear portion 5 merges smoothly into a front portion 6 of slightly 
larger top-to-bottom dimensions than portion 5 and with flat top and 
bottom surfaces 7, 8 and angled shoulders 9 as can be seen in FIG. 3. The 
forward wall 10 of the front portion 6 is angled downwardly as at 11 to a 
flat nose to which is secured a front guard 12. 
The guard 12 is of generally rectangular form when seen in front elevation 
as in FIG. 2 with side walls 13. The guard has a deep V-shaped slot 14, 
the upper portions of the front wall adjacent the upper part of the slot 
being inclined backwardly as shown at 15 to allow a user a better view of 
a work area than that provided by the slot 14 alone. 
The lower (as viewed in FIG. 2) edge of the guard is also slotted as at 16, 
the upper edge of the slot being contoured as at 17 to allow movement of a 
cover 18 referred to in greater detail below. 
The guard 12 also has, in its front face, a hole 12aof generally 
rectangular shape, the hole being positioned just below the tip of the 
slot 14. The guard is secured to the casing by screws 12b. 
The hole 12ais aligned with a hole (not shown) in the flat nose of the 
casing behind the guard 12. 
Extending through an aperture in the upper part of the casing is a slide 
button 19, movement of which controls the operation of an ON-OFF switch 
located inside the casing and shown in FIG. 4 as block 20 and referred to 
below. The slide button 19 is so located as to be conveniently operated by 
the thumb of the hand grasping the rear portion 5. The button 19 may be 
provided with a "lock-off" control (not shown). 
Portion 5 also has air intake slots 21 whilst portion 6 has air exit slots 
22. The rear wall 23 of the casing is formed to receive a cable protector 
24 through which extends a power cable whose end is secured inside the 
casing by means of a cable clamp indicated at 25. 
FIG. 4 shows the tool with one body half removed to reveal the components 
housed within the casing. The body half shown in FIG. 4 has internal ribs 
that support an electric motor unit 26 disposed longitudinally within the 
rear portion 5 of the casing. The motor unit has an armature whose axis of 
rotation lies along the longitudinal axis of the rear portion 5. The motor 
unit is a commutator motor, the commutator end of the motor being located 
adjacent the switch 20. The armature shaft 27 of the motor is operatively 
connected to a drive transmission system and extends through bearings 28 
carried by a support bracket 29 secured to the forward end of the motor 
unit by screws 30 (FIG. 6). 
The bracket 29 has an arm 31 with an integral tubular extension 32 carrying 
a bearing 33. The arm 31 is also formed at 34 to accommodate a thrust ring 
35 and a ball bearing race 36. 
Bearing 33 supports the reduced diameter end of a shaft 37 carrying a bevel 
pinion 38 in mesh with a bevel gear 39 secured to the end of the armature 
shaft 27 as shown in FIG. 4. The upper face of the pinion 38 is in contact 
with the ball bearings of the race 36 which thus supports axial loads 
along the shaft 37. The larger diameter lower end (as seen in FIG. 4) of 
shaft 37 has a pin 40 projecting from its lower race, the pin being 
located eccentrically of the axis of rotation of the shaft 37. 
Pin 40 extends into a tubular roller 41 stepped externally to seat upon the 
upper edge of a liner element 42 seated in a drive member 43 secured to a 
reciprocable shaft 44 described in more detail below. 
The shaft 44 is supported for reciprocatory movement in slots in 
cylindrical sintered bearings 45 held between upper and lower support 
structures 46 and 47. Secured to the forward end of the shaft 44 is a 
clamp 48 by which a cutting tool to be described below can be secured to 
the shaft for reciprocation therewith. The tool projects from the front of 
the guard 12 through the aperture 12atherein. 
The upper support structure 46 is shown in FIGS. 7-11. It comprises a cast 
metal frame of generally rectangular shape when seen in plan as in FIG. 7. 
End members 49 of the frame are contoured to provide curved support 
surfaces 50 for the bearings 45 and guides 51 for the shaft 44. The end 
members 49 extend sideways to form ears 52 each of which has a hole 53 for 
a fixing screw not shown. From the upper faces of the side members 49 
project U-shaped prongs 54 which serve to locate the support structure and 
which engage internal surfaces (not shown) on the body halves 2, 3. 
The lower support structure 47, also a metal casting, is shown in FIGS. 
12-15. In plan view, structure 47 is also of generally rectangular form, 
is sized to match structure 46, and has curved lower support surfaces 55 
for bearings 45 and with guides 56 for shaft 45. The structure 47 has ears 
57 in positions corresponding with ears 52 of structure 46. Each ear 57 
has a hole 58. 
Shaft 44 is shown in more detail in FIGS. 16-18 and it consists of a metal 
strip with slots 60 in its side walls about midway of the length of the 
strip and screw holes 61 close to one end. The holes 61 are staggered and 
between them on one face of the strip is a narrow slot 62. 
Moulded on to the strip in a position allowing it to key into the slots 60 
is the drive member 43 which is of a plastics material. The upper face of 
the drive member 43, visible in FIG. 18, has a central elongate cavity 63 
lying transverse to the length of the strip 44. The inner element 42 
referred to above seats in the cavity 63 as is shown in FIG. 4. 
Attached at one end of the shaft 44 is clamp 48 FIG. 19). The clamp 
comprises a U-shaped block. The base 65 of the block has holes 66 for 
screws 67 by means of which the clamp is secured to the shaft. The ends of 
the limbs of the U are stepped as at 68 so that they seat on the edge of 
the strip. 
When assembled as shown in FIG. 4, the support structures 47 and 46 house 
the bearings 45 and are secured together by screws through the holes in 
the ears referred to above. The shaft 44 is located in the slots in the 
bearings 45 and is orientated so that the end carrying the clamp 48 is 
adjacent the front end wall of the tool casing and the longitudinal axis 
of the shaft is aligned with the hole in the front face of the casing and 
the hole 12a. 
The facing surfaces of the body halves are contoured to provide, when the 
halves are placed together a compartment 69 housing the support structures 
44, 46 and dividing walls 70 that separate those structures of the spur 
gear 39 and pinion 38. This reduces the tendency for lubricants to migrate 
from the gears to the compartment 69. 
The power cable referred to above enters the tool casing through the 
protector 24 and its conductors are connected to the terminal of the 
switch 20. Switch 20 has an actuating plunger 71, movement of which to 
actuate the switch contacts is controlled by a slide 72 that extends, 
inside the tool casing, from the slide button 19. The slide 72 has a cam 
surface 73 shaped to depress the plunger 71 when the slide button 19 is 
moved in one direction and allows the plunger to restore when moved in the 
other direction. The slide 72 is supported by guide surfaces formed on the 
facing inner surfaces of the body halves. The switch 20 is supported in a 
similar manner. 
Formed between the body halves at the front end of the casing is an opening 
74 aligned with the clamp screws. The opening 74 is normally closed by the 
slide 18 referred to above. To expose the opening, the slide 18 is moved 
forwardly. 
The tool can be used for a variety of cutting purposes for each of which a 
particular cutter is used. Examples of cutters are shown in FIGS. 20-26. 
FIG. 20 is a side elevation of a saw blade 75. The blade has a stem 76 by 
means of which it can be mounted in the clamp 48 and teeth 77 along one 
edge. The blade has a tapered tip 78. The teeth 77 have cutting edges on 
both sides so that the saw cuts on both forward and reverse movements. 
To mount the blade, a user moves the slide 18 to expose the opening 74 and 
thereby to gain access to the screws 67. The saw blade is then entered, 
stem first, through the opening 12ain the guard 12 and the stem engaged, 
edge on, in the slot 62. Screws 67 are then tightened to clamp the stem in 
the slot 62. 
After connection of the power lead to a power supply, operation of slide 
button 19 operates switch 20 to energise the motor. Rotation of the spur 
gear 39 is transmitted to pin 40 which, with drive member 43, acts in the 
manner of a scotch yoke drive to reciprocate shaft 44. 
The speed of rotation of the shaft 27 in conjunction with the reduction 
ratio between gears 38, 39 and the "throw" of the eccentricity of pin 40 
are such that shaft 44 reciprocates at a rate of about 10,000 movements 
per minute with a stroke of about 8 mm. A movement is defined as a forward 
and backward action of the blade. 
That high speed of reciprocation combined with the short stroke produces a 
rapid cutting action with little or no vibration. 
The saw blade will cut most types of material especially those of a 
thickness of 16 mm or less. It is, however, capable of cuts up to 30 mm. 
Debris created during cutting is cleared from the work area by air 
exhausting through exits 22 via a channel 79 formed between the clam shell 
halves. 
The saw blade can also be used for so called plunge cutting when the saw is 
used to cut directly into a surface and not on the edge thereof. Such 
cutting action is not accompanied by any "kick-back". 
The tool can also be used with a blade type cutting tool of which examples 
are shown in FIGS. 21-26. 
The cutter shown in FIG. 21 has a stem 80 by which the tool is clamped to 
the shaft 44 in the manner described above. From the stem extends a 
U-shaped jaw 81 with a cutting edge formed round the base of the U at 82 
and along the inside edges of the limbs thereof at 83. The cutting edges 
83 are tapered somewhat as shown. 
The cutter shown in FIG. 21 is used to cut flexible materials for example 
carpets, carpet tiles, vinyl type floor coverings, plastics sheeting, 
rubber sheeting and cloth. 
The edge of the material to be cut is entered between the jaws and the tool 
switched on. The rapid reciprocation of the edge 82 of the cutting tool 
and the short stroke produces a rapid cutting action. 
It wil1 be appreciated that the edge 82 lies at right angles to the 
direction of reciprocation and it is this edge that performs the cutting. 
Edges 83 assist in guiding the tool along a cutting line. Edge 82 is 
rapidly reciprocated towards and away from the material being cut. 
Other configurations of cutting blade are shown in FIGS. 22-24. 
The blade shown in FIG. 22 has a stem 84 and a U-shaped jaw 85. The jaw has 
parallel cutting edges 86 on the inside edges of the limbs of the U and 
arcuate cutting edges 87 at the base. 
Material to be cut is fed into the jaws and cut by the to and fro 
reciprocation of the edges 87. The edges 87 are inclined to the direction 
of reciprocation of the cutting blade. 
The cutting blade shown in FIG. 23 has a stem 88 and a U-shaped jaw 89. 
Short parallel cutting edges 90 are formed at the outer ends of the facing 
edges of the jaw whilst longer convering cutting edges 91 are formed over 
the remainder of those facing edges. Cutting is performed by the rapid 
reciprocation of the edges 91 towards and away from the surface to be cut. 
Those edges are inclined to the direction of reciprocation thereof. 
The cutting blade shown in FIG. 24 has a stem 92 and a single cutting limb 
93 inclined downwardly as shown. The upper edge of the limb has a straight 
cutting edge 94 and an upwardly curved edge 95. 
The blade shown in FIG. 24 can be used in conditions where the material to 
be cut is laid on a flat surface and the limb 93 can be inserted beneath 
the material. Cutting is principally effected by edge 95 which lies 
generally at right angles to the direction of reciprocation. 
The tool shown in FIGS. 25 and 26 has a stem 96 from which extends a rod 97 
faced with an abrasive material. The rod 97 is strengthened by a 
longitudinal fin 98 as shown. 
The tool of FIGS. 25 and 26 is used to cut ceramic materials, and plaster 
materials and like relatively brittle substances. It can be used to cut 
tiles. The tool acts rather as a high speed file. 
If desired, a motor control circuit can be provided to give a two speed 
operation of the motor. For example, a higher speed giving the 10,000 
reciprocatory movements mentioned above and a lower speed giving 8,500 
such movements. The user is then able to select the speed best suited to 
the cutting he requires to do. For example, the higher speed will be 
suitable for materials such as wood and the lower speed will be suitable 
for metals. In both cases, the stroke is 8 mm. 
These speeds, surprisingly, provide effective cutting without, at the same 
time, producing overheating of the cutting tool. In addition, the degree 
of vibration experienced by the user holding the tool is small. 
Equally surprising, it has been established that there is a limited range 
of values for the reciprocatory movement of the cutting tool as for the 
stroke of the latter within which effective cutting action is obtained 
without overheating and an unacceptable degree of tool vibration. 
The range of reciprocatory movement is from a minimum of 4,000 
reciprocatory movements per minute to a maximum of 12,000 movements per 
minute in conjunction with a stroke lying within the range of from 4-12 
mm. 
At speeds much below 4,000, effective cutting is not achieved because the 
reaction goes into the body of the tool and not into the material that is 
to be cut. At speeds much above 12,000, it is found that overheating of 
the cutting tool occurs and damage results to the material being cut. 
Preferably, a range of from 8,500 to 10,000 reciprocatory movements per 
minute is used. 
The stroke of the cutting tool is preferably in the range of from 6 to 10 
mm. 
At strokes much below 4 mm, it is found that cutting does not take place, 
whilst at strokes much above 12 mm, vibration of the tool becomes 
excessive. 
It will be appreciated that the tool does not have to be hand-held, it can 
be mounted upon a stand for use as a stationary tool upon a bench or other 
work surface. 
It will also be noticed that with the cutting blades of FIGS. 21 to 24, the 
limb or limbs of each blade, together with the V-shaped or curved cutting 
edge portion, are disposed below the stem of the cutting blade. That is, 
these specially shaped blades have the cutting and limb edges displaced to 
one side of the axis along which the blade stem is reciprocated. This 
facilitates cutting and provides better cutting control. 
The above described embodiments, of course, are not to be construed as 
limiting the breadth of the present invention. Modifications, and other 
alternative constructions, will be apparent which are within the spirit 
and scope of the invention as defined in the appended claims.