Preparing and using band saws
Tips for preparing band saws for work
Setting the band saw. set the saw, check the clearance between the back part and the rollers rings (no more than 2-3 mm), it must be the same for both rollers. Check position of saw on pulleys (both master and slave).
Tension of band saw. strength of tension is in saw passport. In case of insufficient tensioning of the blade it is possible that the cut is not perpendicular, in case of excess tensioning. the saw breaks.
Belts and rollers. before staring work check condition of rollers and pulley belts. The surface of the rollers should not have signs of wear on the sides. deep grooves. There should be no breaks on the belts, no excessive sawdust buildup.
Running in of the blade. before working under load a new saw should be run in idle for 15-20 min.
The entry should be smooth, only then can you increase the speed depending on the type of wood and the recommended modes.
When sawing with blunt band saws the tension of the saw blade is constantly falling. Some people increase the saw’s tension beyond the recommended. The consequence of such actions is the rapid wear of pulley bearings, rollers, belts, as well as microcracks are formed in the blade. the saw breaks. Therefore it is necessary to sharpen and set the saw in time.
After 1-1,5 h the saw has been working, it must be removed, turned out and hung for 4-5 hours. Only then can it be set and sharpened ( but not vice versa. ).
The tip of the tooth has to be dilated:
1/3 of the tooth height. for sawing hardwood
at A large amount of riving leads to high forces and overloading of the saw, and a poor quality of cut. Indicators of excessive sawing: large amounts of loose sawdust remain in the kerf, scuffs and scratches remain on the surface of the board. The saw jerks.
When insufficient setting – the saw overheats. The indicator is a tightly compressed hot sawdust, wavy kerf.
Optimal set-up. 80-85% of sawdust is thrown out of the kerf.
The indicator on the riving knife should be checked regularly.
First it is necessary to check the setting of the sharpening machine (position of the sharpening blade relative to the saw).
During sharpening metal is removed evenly along the entire tooth profile and trough, without violating the parameters of the saw (blade profile and tooth height). It is necessary to remove as much metal from the tooth flanks as is necessary to remove micro cracks. If the saw has been in operation longer than normal, more metal must be removed.
When sharpening, lightly cut into the blade with the abrasive, remove as little metal as possible, avoid burning and cracking, always use coolant.
The last pass is to grind one back face, so that the grinding waste is in the cutting direction of the saw.
Deburring after sharpening. required procedure.
The choice of sharpening disc is also an important fact in the preparation of the saw. Cheap band saw blades wear out quickly and do not grind evenly within one working cycle.
After sharpening your saw, check the results:
Tooth profile and geometry (compare with the benchmark. the new saw)
The cutting edge of the tooth. the right shape and sharpness.
The presence of abrasive wheel marks
Sharpening is one of the main factors affecting the performance of the saw. This sharpening must be done by a professional. If you do not have such a specialist, it is better to buy a sharpening machine with a borozone (diamond) wheel, which will greatly reduce the dependence of the quality of sharpening on the human factor.
How to use
The first and most basic thing required of the band saw user is to read the manual that comes with each machine. This explains its construction, how to set it up, how to perform basic operations, and other useful information for your work.
The workplace as the “face” of the craftsman. Correctly organized workplace. safety, comfort, and, most importantly, the efficiency of the machine’s operation.
Keep work area clean and tidy. The working table of the machine is worth special attention: it must be free of unnecessary accessories like setting and measuring tools, sawdust and lumps of workpieces. These can fly off and injure the operator under unfavorable circumstances.
Floor on which the band saw machine is installed must be flat, dry and non-slippery for the device not to sway (decreasing thereby the accuracy of the cut), and the master himself could not accidentally slip and fall. It is best to put a dielectric mat (rubber, plastic) next to the saw.
Lighting. The place of contact of the saw-blade and the workpiece should be especially well illuminated, as well as all the controls of the technique. Misplacing a button or failing to follow the marking on the bar, you can irreparably damage the workpiece in a few seconds. over, to work in good visibility conditions is much more comfortable for the user, there is less strain on his eyes.
Climatic conditions also play an important role. High humidity is the most common cause of short circuits and corrosion of metal parts of the machine. And low temperatures double the wear rate of the pulleys and the saw blade. This is especially true for home appliances. Whatever they say, it makes no sense to use a band saw outside in winter. Only professional large machines at fabrication companies can withstand such conditions.
Hands and feet are safe. Safety is a topic to which many craftsmen at home pay very little attention. And in vain! Despite the statement that the band saw is the safest of all sawing machines, negligence at work can be very expensive. Yes, this is not a circular saw or chain saw that tears itself from hands at high speeds, but it is serious equipment with very sharp and fast-moving parts. But observe just a few rules, and no danger can arise.
- First, the master must work in close-fitting clothing, remove all rings, watches and chains, as well as to remove long hair under the headgear to avoid accidental catching on the rotating parts.
- Secondly, do not be distracted. Unauthorized people behind you during sawing are a potential threat even if they give you good advice. The same applies to loud noises and other ways of attracting attention.
- Thirdly, gloves are only required when setting up the machine or, more precisely, when working with a sharp saw blade. The sawing itself is performed without this piece of protective equipment.
- Fourthly, there should never be any staples, nails, or knots in the bars that are handled. Otherwise you run the risk of seeing with your own eyes how the “grass cutter finds the stone” and damage a valuable part of the machine. its tooling.
- Fifth, if the workpiece gets jammed. do not take it out right away, stop the machine, assess the extent of damage and the cause of jamming and only then, armed with everything necessary, take it out from under the band.
- Sixthly, the more securely the workpieces are held during work, the less likely it is that the part will jump off, bounce off and “attack” the master, ricochetting off the rotating at high speed blade.
Last and the most frequent and obvious injury is getting your hands under the cutting element. This is not only unpleasant, but also difficult to repair. In this case, the bones are often affected, which are crushed and then hard to heal. Soft tissues, despite their great pliability, do not look much better afterwards, the scars are quite noticeable. Take care of your hands, they feed you in every sense of the word.
Sharpening band saws.
A band saw needs regular resharpening. Blunt teeth lead to unnecessary stress in the band saw blade. Blunt teeth greatly reduce productivity, quality of the wood and durability of the band saw blade. Also, sharpening becomes more time-consuming. Outward signs of band saw bluntness are: tooth tips become round and shiny; saw tension decreases; quality of cutting surface worsens, appearance of wavy sawing; Average time of band saw’s work between sharpenings should not exceed 1-1,5 hours or 1-1,5 m? round wood.
It is absolutely unreal to correctly sharpen band saw “at a knee”. Sharpening of band saw requires certain skills and appropriate equipment. If the saw is very blunt, it is better to sharpen it in two passes. In this case the saw blade will not overheat. Tooth overheating is extremely undesirable, because it causes changes in the hardness of the tooth and leads to micro cracks. During sharpening, the entire trimmer line should be ground, including the interdentals, to eliminate all micro-cracks. The saw blade should be set in the sharpening machine so that the lower part of the indentation between the teeth is not higher than 2-3 mm from the upper surface of the clamping, otherwise during sharpening the saw blade will vibrate.
All play in the sharpener’s mechanisms must be eliminated, since it would lead to uneven sharpening. Remove burrs during grinding, because they increase local tensions and lead to microcracks in the band saw blade. In many respects, the quality of grinding depends on the selection of the correct grinding wheel. Before use, the grinding wheel must be checked for chipping and cracks. For the sharpening of band saws medium hardness and medium grit, 5-8 mm in thickness are used. If the particle size is too fine, the binder is too hard or the wheels are too thick. there is a risk that the band saw blade overheats. If the particle size is too large, they will form deep scratches that lead to cracks in the band saw during sawing. The grinding wheel must have a profile corresponding to the tooth profile of the band saw. While sharpening the saws, the profile of the sharpening wheel must be constantly monitored, and the mandrel must be resharpened if necessary, since. к. Wear of the sharpening wheel leads to non-uniform sharpening along the length of the saw and changes in tooth angles. When sharpening, the front and back angles of the tooth must be maintained (change as necessary). The softer the wood, the larger the tooth rake angle (tooth attack) should be. A wide enough assortment of band saws is now available on the market, all with their own individual profile (tooth profile and trough) which was selected on the basis of certain calculations and experiments. When sharpening, it is very important to keep the original profile of the band saw blade, i.e. к. its change will cause deterioration of cutting quality and significantly reduce the service life of the band saw blade.
Sharpening errors:. Overheating of the saw;. Sharpening without coolant;. Scratches and galling on the tooth surface;. Improper adjustment of sharpening machine mechanisms (tooth surfaces are not ground completely or evenly);. Looseness in the mechanisms of the sharpening machine;. Incorrect choice of sharpening wheel;. Burrs;. Incorrect sawfeed speeds and grinding wheel rotation;. Reduction or increase of the recommended angle of inclination (sharpening) of the tooth.
Incorrect grinding can significantly reduce the life of the band saw blade.
Requirements for band saws.
Saws must be cleaned of anti-corrosive grease, dirt, sludge, and wood fouling. Lubricant is removed with kerosene or fuel oil, then the saw is wiped dry with a rag. Wood fouling is scraped off with a metal scraper by moving it along the blade, sanding sandpaper.
When getting the band saw ready for operation it is necessary to carry out a number of technological and checking operations, the list of which is given in table 1.
New and used band saws preparation differ in quantity, sequence and composition (volume) of operations. At DZDS during preparation of new saws practically all technological operations are performed in full volume. The structure of operations during the repair of saws depends on their actual state, which is defined during the current inspection after each period of exploitation.
STREAMMETING OF ARMWORDS
Saws preparation includes saw blades and teeth preparation, saws installation into machine and saws repairing. Preparation operations for toothed saws of different designs are practically the same.
Preparation of frame saws. Preparation of frame saws consists of the following operations: detection and dressing of defects in the shape of the blade; control of the tension state of the blade; rolling; the final control of flatness and tension state of the saw’s blade.
Defects are detected by putting a reference ruler on the surface of the saw laid on the reference plate. The gap between the ruler and the blade should not exceed 0,15 mm. Dressing of saw consists in correction of local defects of the blade: convexesВ,tight places Т, weak points С, of the bend And (fig. 44, а). The defective places are corrected by blows of a shimmering hammer on certain points of the saw, laid on the anvil.
Tension state of the blade is estimated by the value of the deflection arrow of the saw 2, bent with radius R = 1.75 m (Fig. 44, б). The deflection range is measured with a ruler and feeler gauges or a special ruler 1 with indicators 3 and evaluated by the arithmetic average of two measurements: with the saw upwards first with one side and then with the other. The optimum degree of deflection depends on the dimensions of the saw and ranges from 0,8 to 0,35 mm.
Rolling of frame saws is one of the measures for increasing the stiffness and stability of the saws in operation. The frame saw heats up in the process of operation, especially at the toothed ring. cutting edge is elongated and under the action of cutting forces loses its stable flat shape. Saw wanders in the kerf resulting in a wavy or curved cut. The frame saws stiffness is mainly ensured by their longitudinal tensioning in the saw frame. The longitudinal tension alone, however, does not give the saws the necessary rigidity because the tensioning force is limited by the strength of the claws and the saw frame that absorbs the tensile forces of all the saws in the post.
The essence of roll forming is that the middle part of the saw blade 4 rolling under pressure between two rotating barrel rollers 5 and 7 (fig. 44, в), The frame saws are based on the roller with the edge outside of the working area. The saw elongates at the roller pass and stretches the adjacent, unrollable parts of the blade. The tension of the roll saw in the saw frame will result in sufficient tensile stresses in the outermost portions of the saw with relatively small tensile forces (Fig. 44, e, f). The number, location, and order of the rolling marks 1-5 are shown in Fig. 44, г.
After rolling, assess flatness and tension in saw blade as described above for non-rolled saw blades. If local defects are found (flatness deviation more than 0,15 mm) additional straightening is performed.
а. local defects of the blade and the order of blows during dressing; б. control of the tensioned state of the blade; roll frame saws; в.the basic circuit diagram: г. location of roll marks; д. Stress distribution in the saw after rolling and tensioning; f. Stress distribution in the saw after rolling
Circular saw preparation. Preparation of circular saw blades includes the following operations: evaluation of flatness and tension state of the blade, dressing of the blade, forging and rolling of saw blade. Flatness of the blade is evaluated by two indicators: by straightness of the disk in different sections and by end (axial) run-out.
The maximum permissible deviations (mm) from flatness depend on the saw diameter and are in the range from 0,1 (for saws up to 200 mm diameter) up to 0,6 (for saws with diameter of 1600 mm). To determine axial run-out the saw is placed on the horizontal shaft of the device. Run-out is measured by the indicator which is perpendicular to the saw blade at a distance of 5 mm from the circle of the teeth hollows at slow rotation of the saw with the shaft
Before starting the measurements the indicator 2 oriented relative to the plane passing through the end face
To do so, a reference ruler is placed on the surface of the radial washer and the leg of the indicator. The zero mark of the dial is set to the big hand of the indicator. To determine axial run-out the saw is set on a horizontal shaft in a fixture 3 set on the shaft 4, clamped with a washer 5 and turn slowly by hand crank 6. The permissible axial run-out (mm) varies from 0.15 (for saws up to 200 mm in diameter) to 0.6 (for saws with a diameter of 1600 mm).
Exceeding the standard values of the flatness indicates the presence of defects of the web, which are divided into general (disks, winglets, bending around the circumference) and local (weak spot, tight spot, bulge, bending). All defects are corrected by dressing the blade
а. scheme of defect detection by checking from both sides;
б. positioning of the hammer blows when correcting defects
The stressed state of the saw blade is assessed by measuring the deflection of the saw blade under its own weight. The saw is placed first with one side up and then the other side horizontal on three supports, equidistant from each other and at a distance of 5 mm from the circumference of the tooth hollows. The deflection of the saw is measured by the indicator of hour type (or by the verification ruler and stylus set) in three points on the circle with radius of 50 mm and the average value of the deflection is calculated. If this value doesn’t correspond to normative one the saw blade is forged or rolled.
Rolling consists in loosening the middle part of the saw by lengthening it when rolling between two working rollers under pressure (cf. fig. 44, в). A flattened saw acquires cross-sectional stability of the toothing as it works.
It is sufficient to roll the saw in one circle with a radius of 0.8/? (where К. radius of the saw without teeth) for three to four revolutions of the saw under the action of the rollers. Roller pressure force for new, non-forged saws when rolling along one circle with a radius of 0.87? is set according to the diameter and thickness of the saw blade and amounts to 15,5. 24 kN (for saw diameters of 315. 710 mm and a thickness of 1.8. 3.2 mm).
Dismounting the BLP
Tooth separation is the operation that establishes further sawing interaction: the material to be sawn is numerically expressed by the deflection of the tooth at a given angle relative to the blade plane. The teeth are set in order to widen the edge of the tooth, thus reducing the friction of the band in the kerf. Over-tensioning causes plastic deformation of the saw’s top tooth. Setting the tooth height too close to the board root line causes fatigue cracks.
Incomplete setting makes it impossible to obtain the full kerf and overloads the saw, causing heating of the blade, which is evidenced by dense, compacted hot sawdust on the board surface. This can be extremely harmful to the saw blade, the cutting intervals will be short and the saw will break down prematurely. Excessive tilting leaves behind large amounts of loose sawdust on the kerf and characteristic scoring and scratches on the board surface.
The set-up can be considered optimal when there is a mixture of 70 % sawdust and 30 % air between the cutting blade and the wood to be cut. In this case up to 80 % of sawdust is removed from the kerf. SP “Bakko Bisov” recommends controlling the setting every 4. 6 m of sawn wood.
Important: You should set at least 1/3 of the top of the tooth and not the center or the entire tooth.
Table 1. Dependence of setting depending on wood type
Recommended set values depending on the type and hardness of wood being sawn (table 1). 1).
In most cases, the tooth rake angle and setting values are selected individually, based on the sharper’s own experience, depending on the hardness, structure, and properties of the wood being sawn.
Construction and materials of the base band and cutting elements of bimetal band saws, production technology, operational quality control make it possible to increase the life of the blade and the quantity of material to be sawn. Reduces time spent on operations such as sharpening and setting. Reduced risk of saw blade damage caused by errors made by the band saw operator. It becomes possible to saw both freshly cut and hard frozen wood including logs with insignificant foreign metal particles.
Resharpening of band saws
In this paragraph I would like to focus on the question of resharpening band saws. Let me start by saying that resharpening the band saw is more of an economic problem than a technical one.
There are three approaches to solving this problem:
- The first approach is this: You saw as long as it saws, then you just throw it away. Some band saw manufacturers, such as Morse in the USA, make a saw that is almost completely unsuitable for resharpening. disposable. This is a cheap steel blade that is thrown away after it dulls the first time.
- The second approach can be formulated this way: You saw with the saw until the saw “undulates,” then remove it and resharpen it.
- The third approach can be summarized as follows: You remove a saw that is still almost perfectly sharp from the machine and only slightly resharpen it.
Consider the advantages and disadvantages of all three approaches:
- The first approach reduces the amount of time the sawmill loses in replacing the blade and also eliminates the need for a sharpener and sharpening station, which is a real savings. If you add to this the fact that it costs about half the price of a fully hardened saw, the savings are obvious. In Russia, however, such saws for some reason cost the same as their technologically advanced counterparts and the savings from the application of this method seem to me unlikely. Sawing to break with such a saw can be 10-12 cubic meters (On the second row). On the installations of the first row, it may not last even an hour.
- The second approach also reduces sawmill downtime associated with saw blade changes. Resharpening the saw less often, which saves the sharper some time, which is well worth the money. However, this approach leads to excessive saw fatigue, more saw material removal during resharpening. As a consequence, the sharpening stone loses geometry, which inevitably leads to a loss of saw tooth geometry and, consequently, to a rapid failure of the saw. Saw cut to breakage with this approach is usually 20-25 cubic meters.
- The third approach is to remove the saw from the sawmill every hour and, after resting, correct it slightly, then go back to work. The disadvantages of this method include frequent stops at the sawmill to change the saw, but this rarely takes more than one minute. The small amount of metal removed during sharpening results in a nearly perfect tooth shape, which in turn leads to increased productivity. With this approach, the saw can be resharpened up to fifty times, and the saw’s tensile strength is up to 80 cbm.
Which of the above methods is preferred can only be decided by the owner of the sawmill, based on the specific economic conditions in which he is.
I’ll allow myself to make a few recommendations on this topic:
- Evaluate whether it is profitable for you to hire a sharpener, weigh whether he will be busy for a full shift, or whether he will mostly walk from corner to corner. Keep in mind that saw sharpening is semi-automatic, and the duties of the sharpener may well be performed by, for example, a shift foreman.
- Objectively estimate the cost of sawmill downtime per minute, this will allow you to objectively assess which of the above described methods of working with the blade to follow, and will also help in communicating with the staff.
Tips for preparing band saws for work
Setting the band saw. set the saw, check the clearance between the back and the sides of the rollers (no more than 2-3 mm), it should be the same for both rollers. Check saw blade position on pulleys (both master and slave).
Tensioning of the saw. the tensioning force is specified in the passport to the sawmill. If the tension of the blade is insufficient, an unperpendicular cut is possible, while in excessive tension. the saw breaks.
Belts and pulleys. before beginning work check condition of pulleys and pulley belts. The surface of the rollers should not have any signs of wear on the sides. deep grooves. Belts must be free of tears, excessive sawdust buildup.
Running in of the blade. before working under load a new saw has to be run in idle for 15-20 min.
Saw should be run in smoothly, only then can the speed be increased based on the type of wood and recommended settings.
When sawing with blunt saws the tension of the saw blade is constantly falling. Some saws need more tension than recommended. The consequences of such actions are fast wear of bearings of pulleys, rollers, belts and also microcracks in a band saw. breakage of saw blade. That’s why it’s necessary to sharpen and unwind the saw in time.
After 1 to 1,5 hours of work remove the saw and hang it up for 4 to 5 hours. Only then can it be reamed and sharpened ( but not vice versa. ).
The tip of the tooth has to be set:
1/3 of the tooth height. for sawing hardwood
At high camber Cause great stress and overloading on the saw, resulting in a poor quality of cut. Indications of excessive sawing: large amount of loose sawdust is left in kerf, burrs and scratches are left on the board surface. Saw is running jerkily.
When Insufficient setting – The saw is overheated. Indicator is tightly compressed hot sawdust, wavy kerf.
Optimal setting. 80-85% sawdust is ejected from the kerf.
Check indicator on the sharpener at regular intervals.
Check first the setting of the sharpening machine (position of the sharpening blade relative to the saw).
During sharpening the metal is removed evenly along the entire tooth profile and trough without violating the parameters of the saw (blade profile and tooth height). It is necessary to remove so much metal from the grooves of the teeth to remove and micro-cracks. If the saw has been in operation longer than it should, more metal should be removed.
When sharpening it is necessary to cut lightly the abrasive into the blade, to remove as little metal as possible, to avoid burning and cracking, the obligatory use of coolant.
The last pass is to grind one back edge so that the grinding waste lies in the cutting direction of the saw.
Deburring after sharpening. mandatory procedure.
The choice of sharpening blade is also an important factor in the preparation of the saw. Cheap discs wear out quickly and do not grind evenly within a cycle.
After sharpening the saw, check the result:
Tooth profile and geometry (compare with the reference, the new saw)
Cutting edge of the tooth. correct shape and sharpness.
Presence of gouges from the cutting wheel
Sharpening is one of the major factors affecting the performance of the saw. It must be a professional of his craft. If you do not have such a specialist, it is better to buy a sharpening machine with a borozon (diamond) wheel, which will greatly reduce the dependence of the quality of sharpening on the human factor.