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I can understand why some people leave dull blades in their bandsaws. If you are uncertain on how to install and tension a new blade, it can be a bit daunting to re-set all the guides, bearings and other setting on a bandsaw, but after you have done it a few times, and you understand the process, it's really not a hard thing to do.
The reason it is so important to know how to change bandsaw blades is because they do become dull quite readily owing to the fact that most of them are made or steel because they need to flex around the bandsaw wheels. Most bandsaw blades for smaller saws, 10, 12 & 14 inch are pure steel blades. These blades heat up during use and over time become dull, and as they become dull, we push harder on the wood, making them even duller and eventually they need to be changed.
The most important step in changing bandsaw blades is to unplug the power to the bandsaw. Some saws have switches in weird and wonderful places that can easily be flipped on by accident when working on the saws. Next the blade tension needs to be released so that the blades is quite loose. At this point you can open the wheel doors to look inside ...
... but before you start taking the blade off, you will need to take that bold or other holding mechanism from the bandsaw's split table because there is no way of taking a bandsaw blade off without taking it through that split. You may also need to release some of the upper and/or lower blade guides and thrust bearing that hold the blades in place during use.
At this point you can now take the blade off and examine the rubber on the wheels. If the rubber tires are cracked, it's best to replace them (you will need to do this sooner or later) and anyway, you will get better performance with newer, more flexible bandsaw tires. Certainly you will need to change them if they are broken or pieces missing ... but if they are in good shape, brush or scrape the wheels to get any caked-on dust and grit off so that they run smoothly.
Installing the blade is almost identical to taking it off, but this time you WILL need to re-adjust the upper and lower blade guides (those little pieces of steel, plastic or wood on either side of the blade) and the Thrust Bearing (some also call a throw-out bearing).
So install the new blade by placing it on the upper wheel first, then the lower wheel, and now is a good time to take up a bit of slack in the blade. Now is also a good time to replace the bolt of leveling device in the split table of the bandsaw.
Next you will want to put full pressure on the bandsaw blade. The method I like best, which works for most blades on smaller 10, 12 and 14 inch bandsaws, is to tighten the blade down then tap firmly with your finger on the side of the blade. When it deflects about 1/8 inch, that will be a good tension amount for that blade.
Before you start to align the blade on the wheel, make sure none of guides or thrust bearings are touching the blade ... now, spin the upper wheel while adjusting the angle of the blade. The angle of the blade is adjusted usually with a locking knob on the upper back of the bandsaw. After you unlock the knob, you can turn it back and forth, as you do this it changes the angle of the upper wheel which is how the tracking of the blade is adjusted. What works best for me is to have the gullets of the blade aligned with the center of the upper wheel tire. I find this is where I get the straightest cuts.
Now that the blade is tensioned, and tracking properly, you can adjust the upper and lower blade guides and thrust bearing. You will need to spin that top wheel frequently to make sure the blade is seated as you make the guide adjustments.
Adjust the blade guides first. They most be positioned so that they do NOT touch the blade's teeth, which means they want to be back a bit from the front of the blade at a point right next to the blade but not touching it. Do this to the upper and lower guides.
Once this is done, now is time to adjust the thrust bearing that sits behind the blade. On both the upper and lower thrust bearing, they want to sit just behind the blade but not touch it. That distance should be about 1/16 inch.
Now you and re-assemble any other parts you may have taken off, like blade guards etc, and test the bandsaw. Before cutting wood, turn the bandsaw on to make sure there is no sounds of the wheels or blade rubbing on anything. If the sound is clear, you are good to start cutting.
One final note, I am often asked if I should leave tension on of off the bandsaw and the answer is ... both. I you are using the bandsaw a lot during the day you can leave tension on. If you only use the bandsaw once in a while, best to leave tension off. The reason for this is because leaving tension on will often re-shape the tires, at least temporarily, and when this happens, when you turn the bandsaw on it will often make a "clunikng" sound and/or vibrate and the tires are now oblong and not round. Running the bandsaw for a time will often smooth them out, but in the mean time some people have mistake this issue as a problem with their bandsaw, which it really is not.
Bandsaws are great tools, having sharp blades and a tune machine will make you bandsawing more enjoyable and give you better results.
Copyright Colin Knecht