By Wood-Mizer, Europe
March 8, 2023
When sawmill blades break prematurely, it’s important to figure out why this is happening so that the problem can be corrected. Let’s take a look at how long sawmill blades typically last, when they should be changed, and why your sawmill blades may break.
How many hours does a bandsaw mill blade have, or how many cubic meters can it cut before needing to sharpen or replace? The answer to the question "How long does a sawmill blade last?" depends on the blade quality and many more factors. In this article, you can learn what you need to pay attention to when working on a band sawmill to avoid premature blade breaks and increase blade life.
Sawmill blade manufacturers do not indicate the exact number of hours or cubic meters the blade should cut. The fact is that there are too many factors affecting the blade condition, which are not under the manufacturers' control. For example, Wood-Mizer is in charge of the sawmill blades manufacturing process and ensures that it produces the blades from quality steel alloys. Wood-Mizer operates state-of-the-art equipment for profile making, hardening, sharpening, setting, and welding blades.
In addition to quality, bandsaw mill blade life also depends on the following factors:
• The sawmill blade maintenance: how you sharpen the blade and set teeth.
• The sawmill: what sawmill you operate, how it’s adjusted, and if the blade is correctly aligned on the mill.
•The wood: are the logs clean? Are there metal inclusions in the logs? Does the sawmill have a debarker?
• The feed speed: the moment the saw blade enters the wood is especially important.
Why Do My Sawmill Blades Keep Breaking?
Some of the causes of premature bandsaw mill blade failure include:
1. The sawmill blade has been used too long.Blades should be replaced with a sharpened one about every 1.5 hours of cutting, or more frequently if cutting dirty wood.
2. The blade guide rollers are worn out. The blade guide rollers ensure the correct position of the saw blade relative to the sawmill bed and the blade stability in the kerf. They are also responsible for the correct tension of the blade. It is essential that the rollers are in good condition without any traces of wear, such as deformation (cone shape), damaged bearings, worn-out roller flange. Worn rollers cause the sawblade vibration and unstable work in the wood, which will lead eventually to a breakage. If the rollers are worn out, replace them.
3. The wheel belts are worn out and too thin. Use genuine Wood-Mizer pulley belts that have a unique form. Wood-Mizer's patented blade wheel belts keep the blade out of contact with the pulley's metal, resulting in increasing blade life. Also, with the belts, Wood-Mizer wheels never need to be straightened or crowned. If the blade wheel belts are worn out, the blade could contact the wheel, causing the blade to break. It is essential to check the belts' condition regularly. The layering of their surface is unacceptable, and they should also not be excessively dirty with collecting sawdust. Usually, both belts are replaced at the same time. In addition, to ensure uniform wear of the belts, it is recommended to swap them from time to time on the drive and idle pulleys.
4. The blade guide rollers are incorrectly aligned. The adjustment of the rollers is checked with the adjustment ruler included in the sawmill tool kit. The gap between the rear edge of the blade and the roller flanges must be at least 3-4 mm and equal for both rollers. Rollers should create some tension and press the blade downwards 6 mm.
5. Check the position of the blade on the blade wheels. Adjusting the idle pulley is usually straightforward, and it is described in detail in the user manual. A more complex operation is adjusting the blade wheel on the drive side. Make sure that after adjusting both blade wheels, the sawblade extends from the wheels equally (average 3-4 mm between the sawblade gullet and the blade wheel rim). If you have questions about blade wheel adjustment, please consult a technician at your Wood-Mizer service center.
6. The bandsaw blade is dull. How do you know when a bandsaw blade is dull? If the blade is dull, the tension constantly drops during operation and makes the sawblade wave in the wood. You cannot solve the problem simply by increasing the blade tension above the recommended value indicated on the sticker on the saw head. It may help but only for a while. For the sawblade to be always correctly sharpened, you need to check regularly the condition of the CBN grinding wheel, replace the oil in the sharpener, and in case of a dirty grinding wheel, cleanse it with a solvent.
Why is the bandsaw blade blunt?
The blade has been running continuously for more than 1,5 hours. The logs are covered with bark and dirt. Sometimes it is enough to cut only 15-20 cm of such a log to make the blade dull. When sawing dirty logs, you need to manually clean the bark before sawing or use a debarker – an option on most Wood-Mizer sawmills. A debarker is a circular blade that removes a thin strip of bark directly in the place where the sawmill blade enters the wood. The blade can also encounter metal objects in the wood, including nails, bullets from wartime, etc. In this case, you should replace the blade for further sharpening and check the blade guide rollers' alignment.
7. Aggressive blade feed. If all of the above on your sawmill is in order, pay attention to the sawing technique. Operators may be sawing too fast trying to exceed targets resulting in blade overload and product quality decrease. Working with aggressive blade feed will result in sawblade overload and “waving” of the blade when it enters the
wood. In this case, the intense signs of contact with the rear edge of the sawblade will be seen on the flanges of blade guide rollers. The blade is also overloaded if its teeth profile and set do not correspond to the type of wood.
8. Errors in the sharpening and setting of the bandsaw blade. This is the most common reason for premature blade breaks. The good news is that modern sharpening equipment uses the CBN grinding technology with a CBN wheel with a blade tooth profile. Using CBN wheels means that the quality of sharpening is less dependent on human errors.