Any processor of the wood at the tape sawmill, undoubtedly, was dealing with problems such as a “wave” or constantly tearing saws, a poor-quality cut, and so on. You can blame the seller or groan the manufacturer of such saws, but most often the cause of all problems with the saws is improper maintenance and handling of the tool. Although this article will deal with band saws on wood, much of it can equally be attributed to saws on other materials.
The saw should correspond to the material, feed rate and, accordingly, sawing. The main parameters of the saw:
Tooth height. this is the distance between the base of the cavity (interdental cavity) and the top of the tooth. Due to the presence of an interdental cavity, the sawdust that is formed during the sawing process is removed from the working area. The volume of the interdental groove should be sufficient to completely remove the sawdust. Sawdust should not completely occupy the interdental space. Otherwise, excess sawdust will be squeezed out on the sides of the blade. band saw, thereby increasing the resistance and friction of the blade on the wood, which will require an increase in effort when sawing. All this leads to overheating of the band saw, the saw is stretched and the so-called “wave” appears. the cut surface becomes wavy. over, additional stresses arise at the base of the cavity, which lead to the appearance of microcracks on the tape web. When the saw blade overheats, its teeth become softer, and they quickly become dull. During operation of the tape web, stresses are concentrated in the interdental cavities and cause microcracks. To reduce such stress concentration, the radius of the recess should be large enough. In general, any scratch and roughness on the saw will serve as the point of origin of microcracks, which will significantly reduce the service life of the band saw blade. That is why the saw must be polished.
Anterior angle of the tooth. This is the angle between the front edge of the tooth and the vertical line perpendicular to the tape web. Thanks to the angle of sharpening, the tooth hooks and cuts the wood fibers. But with a large angle, the band saw will not cut, but tear the fibers, at a high feed speed of the sawmill carriage (or feed the workpiece), while the band blade also vibrates, which will also lead to the appearance of a “wave”. A small sharpening angle gives a smoother cut surface, however, if the angle is too small, productivity is significantly reduced. With a small angle of sharpening angle and too high feedrate of the saw carriage, the band saw will “rub” the wood and not cut, and this leads to additional loads and overheating of the band saw. As a result of improper selection of the angle of the hook, the teeth become dull, cracks appear in the hollows of the teeth. The optimum sharpening angle is selected depending on the type of wood being processed.
Tooth pitch. this is the distance between the vertices of two adjacent teeth of the band saw. It is selected in accordance with the type of wood being processed, the feed speed of the band saw, and the feed speed of the saw carriage (feeding the workpiece). Too large a step increases the tension in the teeth, the saw quickly dulls, the surface quality of the sawn wood decreases. A small pitch gives a smoother cut surface, but requires large energy costs when cutting. In addition, a small step is small grooves between the teeth, which limits the feed speed of the saw carriage of the power-saw bench (at high speeds, high stresses will occur, leading to the appearance of microcracks).
Hardwood requires a small tooth pitch (19 mm). The softer and larger the tree, the larger the pitch of the teeth.
The basic rule for choosing a saw is
The parameters of the saw, cutting speed, feed speed should correspond to the material being processed. As a rule, the manufacturer of saws indicates all the necessary recommendations and you just need to follow them.
Band saw service.
Correct operation and regular maintenance of band saws is the key to their long service life and the condition that allows to obtain a stable quality of the cut surface. First of all, the band saw, before work, must be deployed and the saws free to lie down for 24 hours. This is necessary to relieve uneven stresses. Subsequently, it is better to store band saws in the expanded state.
The main operations for servicing band saws are: cleaning the band saw and visual inspection; sharpening band saw; banding of teeth of a tape cloth; repair (welding) of the band saw blade. The duration of the band saw at the woodworking sawmill, before maintenance should not exceed 1-1.5 hours (or not more than 1-1.5 m? Of roundwood). The need for maintenance may be less and determined by the operator. Some experts recommend, after every 1-1.5 hours of work on the band sawmill, to give the saw a rest of 12-24 hours, so that the band saw "relieves" the fatigue stresses accumulated during operation. If the saw surface ceases to be smooth, a wave appears, the band saw moves backward on the pulleys and guide rollers, which means either the saw has become dull or the tooth alignment has decreased.
Video: Sharpening Band Saws On A Tree In Winter
During interruptions in work (for example, replacing logs or stacking), it is necessary to loosen the saw tension (the saw cools and contracts, especially in winter), this can lead to a break. The tension of the saw in operation should be optimal. A small or large tension on the saw leads to microcracks. During the sawing process, a cutting fluid (water, emulsion, diesel fuel) must be supplied to the sawing zone to cool the band saw, reduce friction against wood, and also to clean the band saw from adhering resin and sawdust. However, even perfect band saw quality and regular maintenance does not guarantee success. A lot depends on the tape sawmill itself.
The saw pulleys of the power-saw bench should be kept clean. Sawdust and wood chips should not accumulate between the saw blade and pulleys. Guide rollers are aligned horizontally and vertically. They must also be kept clean. When the bearings and the rollers themselves are worn, they must be replaced on time, since worn mechanisms cause vibration of the band saw, which affects the quality of the cut and reduces the life of the saw. Manufacturers of band saws, as a rule, set out in detail their recommendations for servicing band saws.
Sharpening of band saws.
The band saw needs regular drag. Dull teeth lead to excessive tension in the tape web. Dull teeth significantly reduce productivity, the quality of the resulting lumber and the life of the band saw. And yet, increases the complexity of sharpening. External signs of a blunt saw blade are: the tips of the teeth become round and shiny; saw tension decreases; deterioration in the quality of the cut surface, the appearance of a wave-like cut; The average duration of the band saw between sharpening should not exceed 1-1.5 hours or 1-1.5 m? round wood.
Correctly sharpening a band saw, which is called "on the knee" is absolutely unrealistic. Sharpening a saw requires certain qualifications and related equipment. If the saw is dull strongly, then sharpening is best done in two passes. In this case, the saw blade will not overheat. Overheating of the teeth is extremely undesirable, this leads to a change in the hardness of the teeth and the appearance of microcracks. During sharpening, the entire tooth line should be sanded, including the interdental grooves, to remove all microcracks. The saw in the sharpening machine should be installed so that the lower part of the recess between the teeth is not higher than 2-3 mm from the upper surface of the clamp, otherwise the saw will vibrate during sharpening.
All backlash in the mechanisms of the grinding machine should be eliminated, as they will lead to inhomogeneous sharpening. The burrs appearing during sharpening must be removed, since they increase local stresses and lead to the appearance of microcracks in the band saw blade. In many respects, the quality of grinding depends on the correct selection of grinding wheels. Before use, the grinding wheel must be checked for chips and cracks. For sharpening band saws, circles of medium hardness and medium grit are used, 5-8 mm thick. If the particle size is too small, the binder is too hard or the circles are too thick. there is a danger of overheating of the band saw blade. If the particle size is too large, then they form deep scratches, which lead to the appearance of cracks on the band saw during sawing. The grinding wheel must have a profile that matches the profile of the band saw tooth. In the process of sharpening saws, you should constantly monitor the profile of the grinding wheel, re-mandate if necessary, because wear of the grinding wheel leads to inhomogeneous sharpening along the length of the saw and a change in the angles of the teeth. When sharpening, it is necessary to maintain the front and rear corners of the tooth (change as necessary). The softer the wood, the larger should be the front angle of the tooth (tooth attack). Currently, a fairly wide range of band saws has appeared on the market, and all of them have their own individual profile (tooth and cavity profile), which was selected on the basis of certain calculations and experiments. When sharpening, it is very important to maintain the original profile of the saw, because changing it will lead to a deterioration in the quality of cut and significantly reduce the life of the band saw.
– Saw overheating;
– Sharpening without coolant;
– Scratches and seizures on the surface of the tooth;
– Incorrect adjustment of the grinding machine mechanisms (tooth surfaces are not polished completely or evenly);
– Backlash in the mechanisms of the grinding machine;
– Wrong choice of a grinding wheel;
– Wrong choice of saw feed speeds and grinding wheel rotation;
– Decrease or increase the recommended angle of inclination (sharpening) of the tooth.
Improper sharpening can significantly reduce the band saw life.
The layout of the teeth of the band saw.
Tooth set is a linear value of tooth deflection by a given angle relative to the plane of the saw blade.
This is one of the most important factors affecting the properties of the saw. When working on a band saw, the wiring is also reduced and the wiring of the teeth of the band saw is required. The size of the wiring, as well as the sharpening angles, depends on the properties of the wood and the diameter of the log. tooth alignment. wider cuts and greater effort when sawing. Small tooth alignment. strong friction, overheating of the tape web, the appearance of a "wave".
The teeth are to be wired on a special machine for sawing. When wiring, the teeth of the saw are bent alternately left and right. Every third tooth is left straight, it acts as a cleaning tooth, removes sawdust from the sawing area, clearing the cut.
Wrong sharpening and wiring. The main reason for premature failure of the band saw. The whole process of sharpening and wiring serves to extend the life of the saw. The teeth should be bred only by the necessary and exactly the same for all teeth value, which is selected depending on the breed (hardness) of the sawn wood.
And finally. Follow all recommendations from manufacturers of band saws and band saws. This is completely justified, as it will save you money and time