Background of the Invention Bandsawing is the preferred method for cutting long pieces of metal into predetermined lengths as a preparation for other operations such as welding, turning and milling.

When using bandsaw blades in maintenance and other smaller workshops it is common to cut a wide variety of work piece materials and sizes. It is not unusual that the operator of the saw machine is inexperienced and not properly trained in the use of the machine. Blades are seldom changed when cutting a new work piece why the choice of bandsaw blade type and tooth pitch is not always done in the optimal way. The upkeep of the machine is often neglected why cuts are frequently made without properly using the chip brush.

The consequence of these circumstances is that the saw blades are frequently prematurely destroyed. They are destroyed because the teeth are broken. The teeth break either because a too coarse a tooth pitch is used when cutting small work pieces such as thin walled tubes or profiles or because a too fine pitch is used when cutting large work pieces or when too high feed rate or too low band speed are used. When too coarse a pitch is used the teeth break because the teeth are overloaded. When to fine a pitch is used, or when too high feed rate or too low band speed are used, or the chip brush is not properly used- the gullets are completely filled and too high pressure is built up in the gullet leading to tooth breakage Bandsaw blades for the above-described applications are normally designed with a variable pitch. This means that the distance between the teeth varies in a predetermined way, dividing said teeth into groups, each group repeating the same variation in tooth distance, so that harmonic vibrations are reduced when sawing. The relative size between the biggest tooth distance in the group and the smallest tooth distance is typically >1.4. Such a blade consists of groups of teeth, each group typically of a length of 1.5". The number of teeth in

each group varies with the pitch of the blade but is typically odd in number. A blade with a 6/10 teeth per inch pitch typically has 11 teeth in each group. The meaning of the designation"6/10"is that the biggest tooth gullet in the group has a size corresponding to a regular 6 TPI blade and the smallest gullet has a size corresponding to a 10 TPI blade. The clearance angle of the teeth is typically 35° and the clearance side of the tooth, or the back of the tooth, is straight, leading to a small bottom radius of the gullet. The size of the bottom radius of the gullet is typically less than a 1/2 of the dept of the gullet.

The deep gullets with small radii increase the risk of swarf being locked in the gullet. The swarf is often in the form of spiral shaped chips that get trapped between the sides of the deep, narrow gullets. The radius of such chips is typically about 1/2 of the depth of the gullets i. e. bigger than the radius of the gullets, thereby causing the chips to be looked in the bottom of the gullets.

It is known to set different teeth within a group according to a predetermined setting pattern. The setting pattern of such a group normally follows the order:-0-R-L-R-L-R-L-R-L-R-L-i. e. the first tooth in the group is unset, the next is set to the right, the following to the left etc. with only one unset tooth per group.

The setting operation is done one group at a time. When setting up the setting machine it is of great importance that the correct tooth is left unset. If the wrong tooth is left unset the setting hammers will hit the other teeth in the group in such a way that the teeth or the edges are deformed in an unwanted way. This leads to high amount of scrapped material in the production of such bandsaw blades.

The design of the gullets of traditional blades of this kind is such that all gullets in the group are proportional i. e. they have the same relationship between tooth distance, gullet depth and gullet radius. The chip holding capacity of each gullet in the group is proportional to the cross sectional area of the gullet. The chip holding capacity of the gullets in such a design is limited by the cross sectional area of the smallest gullet in the group. The other, bigger gullets in the group are unnecessarily big because all their dimensions are proportional to the tooth distance in relation to the smallest gullet.

A gullet that has a tooth distance that is 20% greater than the smallest gullet in the group will need 20% more chip capacity than the smallest gullet. By making all dimensions of the gullet proportional to the smallest gullet the chip holding capacity will be 1.2 x 1.2 = 1.44 i. e. 44% more than the smallest gullet.

This will result in gullet depths that are deeper than necessary, leading to reduced beam strength of the blade. Reduced beam strength will lead to out-of-square cutting at lower sawing loads compared to a blade with higher beam strength.

Technical Problems Taking the background of the invention into consideration it is a technical problem to produce strong bandsaw blades, both in the sense of having teeth that are not easily broken and in the sense of the beam strength of the blade.

It is a technical problem to reduce the risk that the teeth break, either because they are overloaded or because the gullets are filled with swarf.

It is a technical problem to set the teeth without unwanted scrap caused by mispitching.

It is also a technical problem to maintain beam strength and still have gullets with sufficient chip capacity.

Solution The present invention teaches a new tooth design that overcomes all of the problems described above. The bandsaw blade with such teeth is presented in the following claim 1. Various advantageous embodiments of the present invention can be found in the dependent claims.

Advantages The advantages of a bandsaw blade according to the present invention are that both the tooth strength and the strength of the beam can be sufficiently high, that the gullets will be dimensioned to the required chip capacity and that unwanted scrap due to mispitching while setting the teeth is reduced.

Brief Description of the Drawings So that the invention will be more readily understood and further features thereof made apparent, the invention will now be described in more detail with reference to exemplifying embodiments thereof and also with reference to the accompanying drawings, in which: Figure 1 schematically shows a known bandsaw blade,

Figure 2 schematically shows a known bandsaw blade with teeth divided into groups, Figure 3 schematically shows teeth of a bandsaw blade according to the present invention, and Figure 4 schematically shows an inventive bandsaw blade with a variable tooth distance.

Detailed Description of Preferred Embodiments Figure 1 shows a bandsaw blade 1 with teeth 11,12 separated by a gullet 13. Parameters pertinent to the present invention are the tooth distance A, the clearance angle B, the radius C of the gullet 13, and the depth D of the gullet 13.

Figure 2 shows a known bandsaw blade where the teeth are divided into groups, each group repeating the same variation in tooth distance. The figure shows that the smallest gullet 13a and the largest gullet 13b differ in all the above- mentioned parameters.

It can be seen in the figure that the smallest gullet is not able to handle as much swarf as the largest gullet. The largest gullet is on the other hand deeper than the smallest gullet, reducing the beam strength.

Figure 3 shows a versatile bandsaw blade according to the present invention presents a tooth design with a tooth that is provided with a tooth edge stronger than on previous designs. This is achieved by using clearance angles B' of the teeth 11', 12'that is smaller than 35°, for example 30°, and a strong base of the tooth. The back 12'a of the tooth 12'is curved 12'b, for the sake of simplicity shown on the tooth 12', the same is true for tooth 11'and every other tooth, to lead to a large bottom gullet 13', the radius C'of which is larger than 1/2 of the depth D' of the gullet 13'. The radius C'can for instance be approximately 3/4 of the depth D'of the gullet 13'.

This design has proven to give higher resistance to tooth breakage compared to the known design, both against the overload caused by too coarse a pitch and overload caused by the gullets being filled by swarf. The radii of the chips, typically being 1/2 of the depth D'of the gullets, will be substantially smaller than the radius C'of the bottom of the gullets thereby being easily ejected from the gullets even without the use of a chip brush.

Figure 4 shows the variable tooth distance of the blade according to the present invention. This is made with a relative size between the biggest tooth distance A'1 in the group and the smallest tooth distance A'2 that is substantially smaller than used before (= approx. 1.3). The result of this is that the gullet capacity of the smallest gullet 13'a in the group is substantially bigger than the smallest gullet 13a in the previously known design. This will further reduce the risk of teeth being broken because of filled gullets.

The setting pattern of the new blade is-0-R-L-0-R-L-etc. The combination of the small difference between the biggest and the smallest gullets and the set pattern will allow the blade to be set in different ways. It does not matter which tooth is left unset, set to the right, or set to the left. When producing such a blade it therefore does not require the difficult set up procedure required by the known design and the risk of destroyed teeth and high scrap numbers is eliminated. The number of teeth in each combo group can be any number >4.

The design of the gullets of the blade according to the present invention is such that the depth and radius of any gullet is proportional to the square root of the relation between the tooth distance of this any gullet and the tooth distance of the smallest gullet in the group of this any gullet. A gullet that has a tooth distance that is 20% greater than the smallest gullet in the group will need 20% more chip capacity than the smallest gullet. By making all dimensions of the gullet proportional to the square root of the relation between the tooth distance of the gullet in question and the smallest gullet in the group the chip holding capacity will be square root (1.2 x 1.2) =1.20 i. e. 20% more than the smallest gullet. This will result in gullet depths that are not deeper than necessary, leading to increased beam strength of the blade compared to normal blades.

It will be understood that the invention is not restricted to the aforedescri- bed and illustrated exemplifying embodiments thereof and that modifications can be made within the scope of the inventive concept as defined in the following Claims.