The technical area of the invention

The invention in question relates to a sawblade preferably intended to be used in a bowsaw, wherein the saw-teeth are grouped in several groups, and also a procedure and a device to produce this sawblade.

Technical background

Within the above mentioned technical area many different solu¬ tions exist to improve a sawblade by varying and changing the teeth of the sawblade in differnt ways to increase the safety and efficiency when using a saw.

The most common sawblades on the market are group-toothed blades (that is blades with irregular distance between the tooth-tips) the number of teeth can be 3, 4 or 5 teeth per inch.

When manufacturing group-toothed sawblades a punching tool consisting of punch and die with the same profile as the blade beeing produced is normally used. With this tool one can only produce sawblades with one type of toothing.

One purpose in making a sawblade with teeth in group is to neutralize the resonance that easily occurs in a sawblade that has been fastened in an arc. The blade may then act like a string on a guitar, that has a given tone.

In a sawblade without teeth in group vibrations easely occur, as the tooth-tips of the sawblade can strike against the wood-fibers. This can be compared to the tooth-points acting like a number of small axes chopping off the woodfibers at an even frequency .The chance is great that this frequency is equivalent with the that of blade itself, so that resonance occurs, causing vibrations in the sawblade.

This can be shown by the following example. If you assume that a 30" (762 mm) long blade with 150 teeth has a tension that gives a normal A (440 Hz) in frequensy and the saw is moved at a speed that gives one sawstroke in 0.34 second, which is a fairly normal speed, the points will strike against the treefibers with a fre¬ quency that corresponds with the sawblades own frequency . This leads to resonance and accompanying strong vibrations.

Corresponding risks for resonance naturally exist at other sawing speeds that are equivalent to different under and overtones, like an octave or a quint etc. The result of this is that the sawblade tends to brake in the sawtrack which leads to more heavy sawing.

These problems has been solved through the arrangement of irregu¬ lar distance between the points.

This causes several tones to occur ( dissonance) . These vib- , rations neutralize each other making that the saw goes "quiet", that is, free of vibrations and accordingly runing easier in the track.

Saws for fast cutting have relatively big teeth. With this type of toothing it is difficult to begin a sawstroke, that is, from a level where the speed of the sawblade is 0 and hereby beeing able to make a sawstroke avoiding that the sawblade jumps ris¬ king an injury both in the hand ^hat is holding the work-piece and the workpiece itself. Injuries of this kind are one of the most common on cvonstruk ing-sites, they cause much inconven¬ ience and a lot of unnecessary suffering.

One solution to the problem with jumping bowsaws is the so cal¬ led push-off sawblade, that is, a sawblade with fine teeth in the front part of the blade, with the purpose to make the start of the stroke easier, followed by bigger teeth for higher per¬ formance .

When manufacturing a sawblade with finer, closer toothing in the front of the blade, within the intention that one at the start of a cutting (that is, from the level where the speed of the sawblade is 0) shall be able to make a sawstroke without the saw jumping, one has up to now had to cut the blade in several different tools.

Some examples of different constructions and product ionmethods for sawblades are shown in EP-A1-205 245, DE-C-565 136, FR-A-1 586 519 and GB-A-2 177 344

Short presentation of the inventio idea.

The purpose of the invention in question is to provide a sawblade for instance for bowsaws (arcsaws) , that unites the advantages of both the types of blades mentioned above and at the same time is easy and cheap to manufacture.

In accordance with the inventionidea one receives a sawblade with at least one push-off part and at least one part with teeth in group, werein the part of the blade with teeth in group includes a number of groups of preferably V-shaped notches in the blade, wherein each pair of notches defines a sawtooth, and wherein each group is comprised of an even number of notches, and that an ima¬ ginary line A that is drawn between each alternate bottom of a se¬ lected group, e.g. notch one, three, five, etc. is a straight line which establish a small angle, alfa, to the longitudinal direction of the sawblade whereby the bottoms and the tips are uniformly distributed along the line.

According to the inventionidea a group-toothed sawblade is produ¬ ced by means of a tool comprised of a punch and a die, wherein the punch cutting out the sawteeth is constructed fully symmetrically with essentially V-shaped points, wherein a sawblade-blank conven¬ iently in the form of a steel-bandis fed through said tool, and th blank is punched in at least two stages whith one and the same too 'wherein the blank for the purpose of forming one group in a group- toothed part in a first stage from a starting position is tilted a small angle, alfa, relative to the punchingtool and the blank is punched against the die, whereafter the blank is advanced through the tool a distance which corresponds to half the width of a tooth calculated on a punchingtool tooth,

and the blank in a second step is tilted back relative to the tool in an opposite direktion to at least the starting position and is punched, werafter the method is repeated until the de¬ sired number of groups hane been formed.

By combining the quiet stroke of the grouptoothed sawblade with th safety of the push-off toothed blade, one receives a sawblade that is easy to saw with, since the resonance in the blade almost has been eliminated and the chance that the saw jumps and causes the user injuries in the start is very small.

Short description of attached drawings.

The invention will below be described with reference to accom¬ panying drawings.

Fig nr . 1 shows a grouptoothed standard sawblade.

Fig nr . 2 shows a sawblade with push-off teeth at one end.

Fig n . 2a shows a sawblade which is both push-off and group¬ toothed according to the invention.

Fig nr 3. shows a punching device for the manufacturing of a conventionel 1 grouptoothed sawblade.

Fig nr 4. shows a punchingdevice for manufacturing of a saw¬ blade according to the invention.

Fig nr 5. shows how a sawbladeblank is punched according to the invention, when the punchtool is tilted in relative to the saw¬ bladeblank.

Fig nr 6a-6e. shows how a sawbladeblank is punched according to the invention, when the sawbladeblank is tilted relative to the punchtool .

Description in detail of a preferred performance of the invention

In fig. 1 and 2 the preknown technique is presented.

In fig.l is shown a grouptoothed sawblade with several groups 4 that in each group has three sawteeth 1,2 and 3 and between each group 4 a space 5. All teeth are equal and all groups have the same amount of teeth. In fig.2 a sawblade is shown that has one part 6, at one end, which is push-off toothed to make the starting up of every sawing operation easier.

In fig.2a. is shown a push-off and grouptoothed sawbladeaccording to the invention. At one end of the sawblade the push-offtoothed parts 6, 6a are shown connected to a grouptoothed part 7.

Fig 3. Shows a standard punching device for manufacturing grouptoothed sawblades. The sawbladeblank is placed in a punching device including the punch 8 and the die 9 which have the same profile as the readymade sawblade. The tool according to the invention, is shown in detail in fig. 4 and has the same tooth-hieght , tooth-width, tooth-side and tooth-space all along the punchtool. Each tooth on the punch-tool punches two different V-shaped notches in each group, in the complete group-toothed sawblade ,

As shown in fig. 2a a sawblade according to a discoursed performance, consists one push-off part, and one grouptoothed par .

The blade is intended to be used in a bowsaw (arcsaw) . The grouptoothed part of the blades contains several groups of preferably V shaped notches in the blade, and each pair of notches defines one sawtooth. Each group consists of an even number of notches. One first imagined line A, whith is drawn between every other bottom in a arbitrary group for instance notch one, three, five etc. is a straight line and defins a small angle (alfa) with the longitudinal direction of the saw¬ blade. The bottoms are uniformly distributed along the line.

A second straight imaginary line B, drawn between remaining bottoms e.g. notches two, four, six etc. is a straight line which defins a small angle (beta) with the longitudinal direc¬ tion of the saw blade. The bottoms are distributed uniformly along the line B.

A third imaginary line C drawn between the points of the teeth of the sawblade, is a staight line which extends parallel to the longitudinal direction of the sawblade. The points of the sawteeth however are distributed unenenl alon the line C.

In fig. 5 and 6a-5e is shown a device for manufactu ing a push- off and/or a grouptoothed sawblade S containing a punchingdevice in the shape of a punch 8 collaborating with a die 9 for punching a sawbladeblank. The working parts of the punch 8 are symmetricall shaped. The device further more includes slides that guide the blank through the punchingtool. The arrangement is provided with means that facilitate a certain tilting of the blank both ways obliquely relative to the punch 8 and the die 9.

In Fig.3 a fourth imaginary line' D is shown, which is drawn throug the punch 8 where the width of the tooth 1 is the same as the dis¬ tance to the next tooth 2. The arrangement is further mere provide with means to vary the distance between the blank and line D.

In this discribed preferred performance tilting and distance- variation are brought about by the slides.

The arrangement also includes means for advancing the blank throug the punchingtool .

Means for tilting, distancevariation and advancing is preferably controlled automatically, for instance by a computorprogram in advance stored in a microprocessor or a computor.

The manuf ctu ing process of a grouptoothed sawblade with the describe.:- device is done as follows. A sawbladeblank preferably in the shape of a steelband is fed through

the punchtool 6,9. The blank S is punched in at least two steps with one and the same tool. The blank is tilted obliqely a small angle (alfa) relative to the punchtool in a first stage from a starting position for the purpose of forming one group in a group¬ toothed part 7. The blank S is then punched against the die. The blank is thereafter advanced through the punchtool a distance which corresponds to half the width of a tooth calculated on a punchtool tooth. In a second step the blank is tilted back relative to the punchingtool to at least the starting position and. tilted to a small angle (beta) relative to the punchingtool in the opposite direction to said angle (alfa) and punched. ^' The procedure is repeated until the desired number of groups have been formed.

The angle alfa is normally equivalent with angle beta.

In the purpose of obtaining a push-off part the sawbladeblank may in one procedurestep be oriented parallel with line D, but sligthiy spaced from as to obtain relatively low sawteeth. Hereby a deter¬ mine! number of sawteeth will be accommodated between two mutually adjacent punchtool teeth. Thereafter the blank is punched and ad¬ vanced a distance corresponding to one of the teeth in the number of teeth that are accommodated between two mutually adjacent punchtool teeth. The procedurestep is repeated until a desired iegth of the push-offpart is obtained.

To obtain a transition between a push-off and a grouptoothed part one or both of following methods can be used, in the first the distance between the blank and line D is reduced to obtain a sec¬ tion of the push-offpart that has slightly higher teeth. In the second, the angles alfa and beta are increased successively, at a predetermined number of groups at the transition from a push- offtoothed part,

to a grouptoothed part, from a small angle to a predetermined maximum angle at the same time as the distance between line D and the blank is decreaced successively.

As mentioned above the procedure may be run automatically by means of a computerprogram stored in a microprocessor or a com¬ puter, which is a great advantage as the sawblade due to this can be made in an endless number of variations.

Within the limits of the invention modifications may exist as the tool can be tilted instead of the blank in correspnding degree, and the toolcan be moved in relation to the blank at the push-off- toothing. The angle alfa and beta may be varied one bydone and in relation to each other within the limits of the invention.