Finding the correct blade tension always seems to be something of a mystery among woodworkers. There are all kinds of methods out there, such as plucking the blade like a guitar string until it produces a clear tone of a specific musical pitch. However, in an effort to finding the best method to adjust blade tension, we are going over some practical ideas on tensioning blades so that you can adjust your saw for accurate cuts. But first, we will be talking about the importance of bandsaw blades and tension.
Tips: If you are not on a budget, bimetal, carbide-tipped and spring steel blades can be tensioned significantly tighter than carbon blades. That means they will be more rigid and less likely to deflect and wander in difficult cutting situations, making them an ideal choice for resawing. You can always weld your own bandsaw blades if you are confident in your skillset or get a good bandsaw blade here.
Finding the right tension for your bandsaw
Bandsaw blades require tension and lots of it to consistently product straight, uniform cuts, especially in thick or dense stock. Most blade manufacturers recommend 15,000 psi to 20,000 psi for a common carbon-steel blade.
However, bimetal, spring steel, and carbide-tipped blades are so much stronger than carbon steel blades, so manufacturers recommend a much higher tension: 25,000 to 30,000 psi. Why do bandsaw blades need so much tension? For beam strength. The tighter the blade is stretched, the more rigid it becomes and the less tendency it will have to deflect in the cut.
You only need maximum tension for the most demanding cuts, such as sawing dense hardwoods or stock of the maximum thickness that will fit under a saw guide. In simple circumstances. you can back off the tension a little.
All blades, regardless of width, require the same amount of tension for maximum beam strength. The variable factor is the amount of pulling force needed. For example, it takes approximately 200 lb.of force pulling on a 1/4 in. -wide by the 0.025-in.-thick blade to create 25,000 psi of tension. Conversely, a 3/4-in.-wide by the 0.032-in.-thick blade will require approximately 800 lb. of force to create the same 25,000 psi of tension.
How to measure tension
Bandsaw blade tension scales are notoriously inaccurate. Tests conducted by consumer woodworking magazines have shown this, and my own tests using six different bandsaws confirmed the results. For my tests, I used a blade tension meter that clamps to the blade and gives an accurate reading on a dial indicator. The readings of all the saw tension scales that I tested, including those on the expensive floor-model saws, were lower than that indicated on the meter. Although the scales on the large machines were close to being accurate, the scales on the 14-in. saws were way off. To make matter worse, the spring used in the tension scales on bandsaws weaken with age, further reducing their accuracy.
How do you know when blade tension is correct? The most accurate way is to check it with a tension meter such as the one I used in my tests. You should do that if you just change your bandsaw blade as well. Tension meters are expensive and there is no other way as accurate.
A good place to begin is to tension the blade until the meter reads proper tension for the next wider blade. For example, if you are tensioning a 3/8-in. blade, I would set the scale to 1/2 in. This works most of the time since most sawing operations don’t’ require maximum tension.
Another method is to test the tension by the amount that the blade will deflect sideways. First, you should set the upper guides about 6 in. off the table. Then using a moderate amount of pressure from my index finger(while the bandsaw is turned off – check bandsaw safety rules here), push the blade sideways. You don’t want the blade to bow more than 1/4 in. You will need to sense for how much pressure is moderate by yourself.
To some extends, both methods work decently as in most situation, maximum blade tension is not necessary. I always test the blade tension with a trial piece before making cuts in an actual workpiece. If the blade wanders in the cut (assuming other factors such as blade sharpness and guide setting are correct), I’ll gradually increase the blade tension.