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How to use and maintain the Wood-Mizer blades
Wood-Mizer manufactures not only sawmills but also blades.. Our main goal is to ensure fast accurate cutting in many types of timber. We have already had considerable success, our technology is spreading and we are now selling blades in 107 countries of the world. However we continue to work on improving our blades. The blade can lead to success or failure of the sawing operation and that is why it needs special attention from operators and sharpeners.
Let us view main rules of band-saw blade usage.
The choice of blade profile to be used for a particular job depends on the timber to be sawn.. Hook angle, tooth set, sharpness and correct tooth height are the four most important factors determining the ability of the blade to saw.
It is important to put the blade on pulley wheels correctly. The distance from the tooth gullet to the wheel edge should be strictly defined. This distance depends on the sawmill model.
It is important to control the condition of the wheel belts. If the blade is less than 0,8 mm from the wheel, you should change the belt. It is important to use a belt with the correct thickness. It is important because the blades sit on the belts at a high pressure. Any bulge on the belt increases pressure on the blade. It leads to sawmill vibration and reduces the blade life. Sometimes sawdust accumulates under the belt. This leads to the same consequences as a bulge on the belt and should be cleaned out regularly.
The blade should be supported on both sides of the log as close to the log as possible. The correct position of blade guide rollers provides additional blade stability while sawing. As a result you will saw at a higher speed, blade life increases and the blade saws more timber. How to adjust the blade guide rollers properly?? Incline the rollers towards the blade rotation 3î, ensure a 3 mm clearance between the roller flange and back of the blade, lower the rollers (push the blade down) 7 mm, and control the vertical tilt of the blade.
The blade tension should be – 150-170 atm. Let us view the blade parameters separately.
If you look after your blades properly and maintain correct mill alignment you can sharpen a blade from its original width down to about 21mm and still get good cutting performance.
The blade life and accuracy of sawing also depend on the blade thickness. Theoretically the thinner the blade the longer you can use it because there is less transverse stress in the blade and therefore the greatr the flex life of the blade. On the other hand, thinner blades tend to be more easily influenced by the log conditions and can give inaccurate cutting.
The tooth profile has being designed and refined over many years. Today the profile of the Wood-Mizer blade is an industry standard.
Hook angle, tooth set, sharpness and correct tooth height are the four most important factors determining the ability of the blade to saw. All of them affect the output and accuracy of sawing.
Tooth spacing is the distance between the teeth. This parameter always remains the same. Sharpening correctly on approved sharpening equipment will not change this dimension.
Tooth height is the distance from the lowest point of the gullet to the highest point of the tooth.
The Gullet is the space between the teeth which "carries out" the sawdust created during sawing. The tooth height should be big enough to allow it to carry out all the sawdust. While sharpening you should take enough material from the gullet to maintain the correct tooth height – 4,8-6,4 mm. On the new Wood-Mizer sharpener with a CBN wheel the hook andgle and the tooth height are fixed parameters. The Gullet is about 30% of the tooth spacing. To increase blade life the gullet should be free from scratches, burrs and burn marks. If the sharpening was performed correctly then burrs should be able to be removed easily with a wooden scraper. The presence of heavy burring indicates that the grinding has left many microscopic cracks which can migrate into the body of the blade during the stresses created during the cutting process.
Hook angle is the angle created by the leading edge of the tooth in relation to the back of the blade. This angle allows the tooth to cut into the during sawing. The tooth should remove enough material for the blade to penetrate the wood on its own. The hook angle is selected in order toalow the blade to do the cutting without being forced into the timber. If the hook angle is too big in comparison with the feed rate then you get vibration, a rough surface and low quality sawing. The blade will be pulled too quickly into the log, and at the same time its front edge can come too far off the wheels. If this angle is too small then you will have to "push" the blade into the log. The result will be lower feed speeds, lower sawn output and the blade will heat up causing damage to the blade and poor quality cutting. The type of wood and performance standard determines the hook angle value. We recommend hook angles of 10°, 12,5° or 15°. For hard, medium an sof timbers respectively.
Radius of the Gullet is built into the blade to hold and remove sawdust. The design of the gullet should also help to support the cutting edge of the tooth by spreading the cutting loads and dissipating heat generation Too small radius leads to the blade breakage because the cutting stresses are concentrated in oine are of the gullet.
The sharpening equipment should be kept in good condition, there should not be any slack in the components. Vibration from the grinding wheel or from the motor can cause damage to the tooth leading to cracks and eventually breakage. You should remember that only well-maintained equipment can produce high-quality sharpening.
Grinding wheel maintenance
The profile of the blade can be changed by altering the profile of the grinding wheel during dressing.. Changing the tooth profile means that you change the cutting characteristics of the blade. As previously discussed it is very important that the tooth profile is correct for the timber being cut and thus it is important to dress trhe grinding wheel correctly to maintain the desired profile.
Tooth set is a distance that the tooth is offset relative to the body of the blade. The set is a very important factor. The more the tooth is set the wider will be kerf and the more power is needed to cut. The purpose of the set is to create clearance for the blade through the timber. This clearance is called the "kerf" In fibrous softwoods you need more kerf than in hardwoods in order to remove the sawdust effectively and thus avoid heating up the blade. Frozen woods require a smaller kerf.
How to understand whether your blade is set correctly
The set is optimum when there is a mixture of 65-70% sawdust and 30-35% air between the blade and wood in the kerf. With a blade that has the correct set, it should carry out about 85% of the sawdust created during the cut.Too much set will result in inefficient cutting an poor surface quality, too little set will result in compacted sawdust being left on the cut and this will heat the blade. Sawdust should be warm to the touch but not cold or hot and should be chiplike in its quality. One more very important point:- you should set only the upper 1/3 of the tooth. Do not set the whole tooth, only the sharp point on the very end of the tooth should do the cutting. Again – ensure that the tooth setter is well maintained.
Tooth set point
The tooth should be held in the setter clamp just level with the bottom of the gullet, and the set point that actually presses against the tooth to create the set should be positioned in the middle towards the top of the tooth. If the set point is to low you will deform the body of the blade leading to premature breakage. If the set point is too high you will generate a rough surface and uneven cutting with poor sharp-life. Blade cleaning When you remove a blade from the mill you should clean the blade removing all sawdust and pitch. If you sharpen a dirty of damaged blade you will clog up the grinding wheel which will result in poor quality sharpening and reduced grinding wheel life.
Loosen blade tension after working
During sawing the blade warms up and expands, as the blade cools it relaxes, and so the tension should always be released when not working. An operator's abilities play dominant part in maximum output getting and blade usage lifetime increasing. An operator controls many conditions and factors affecting on sawing process. Cutting rate depends on the following factors:
Type of wood. Softwood has irregular density, annual rings, and knots. It is important to adjust cutting rate. Hard wood is normally of a more regular density (except of logs of low quality) and can be sawn faster and with constant rate. Different densities makes a blade saw in different ways. Usually the most difficult moment is when a log is partially frozen.
Log diameter. The larger the diameter, the longer the cut and therefore more sawdust has to be removed by the gullet.
Moisture Content. The drier the logs the harder they are. Sometimes very dry softwood logs need to be cut with the same profile of blade as hardwood logs.
Logs cleanliness. When sawing dirty logs you will need to sharpen the blade more frequently than usual. Sharpening decreases the blade width and thus your overall blade life will decrease
Blade guide rollers. Correct positioning gives the blade stability in the cut. This stability allows you to saw at the highest possible cutting rate. Blade usage lifetime
Fatigue cracks are one of the factors limiting the blade life. Cracks appearing on blades is explained by metal fatigue because of the stresses caused by the cutting process or by incorrect sharpening or the wrong choice of profile for the material being cut. It can also be caused by poor steel being used in the manufacture of the blade.
The cutting speed
Having chosen the correct tooth profile and blade dimensions for the timber being sawn, saw as quickly as you can while still getting accurate cuts and high-quality timber.
Author: Yury Romanovich, Customer Service Manager
Wood-Mizer Industries, Moscow brunch
+7 495 788 72 35
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