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How To Tension A Bandsaw Blade

Tension can make or break your blade's performance. Most people don't have a gauge to measure PSI (pounds per square inch). Few of us can correctly identify a blade's musical pitch either. (However, if one of these methods works for you, by all means use it.)

To find the correct tension, you can start with the tension scale on your saw, but you will probably need to fine tune the adjustment. With the saw unplugged, increase the tension on the blade until pushing on the side of the blade with your finger using a moderate amount of force deflects the blade about a 1/4" from its normal position. Do this along an unrestrained stretch of blade. (Back the guides out of the way first if only the front stretch of the blade is accessible on your saw.) The exact way that you push is not as important as doing it the same way every time, so the you develop a feel for what is the right tension for a particular blade. You can initially learn the correct tension experimentally by cutting a piece of scrap wood using different blade tensions. A blade that is undertensioned will be extremely sensitive to changes in feed pressure (more on this under Operator Technique) and you will have a tendency to bow in thicker wood. A bow can also be caused by other reasons. Too much to tension for one person may not be for another depending on the machine being used and personal work habits. When too much tension is put on the blade, premature blade breakage and poor tracking can occur, but most important, you can damage your machine by trying to make it reach a blade tension greater than the machine was designed to operate at. Good results come easier when using blades that serve your specific needs, rather than forcing one blade to do all jobs.

Can you over tension a bandsaw blade?

The answer is yes, so be careful not to over tension your bandsaw blade. While the blade can take high tension, it is always best to use an amount of tension that gets adequate cutting results and no more. Extra tension just makes for more stress to the blade and all of the components of the band saw. Overtensioning a bandsaw blade also risks metal fatigue which can shear-off a bandsaw's wheel shaft. If metal is flexed back and forth enough times under enough force, it will break. Bandsaw shafts are designed to tolerate a certain force. It is a force well above the level of force exerted by in normally tension bandsaw blade, i.e., a blade tensioned according to the saw scale. At this tension or "endurance level" the shaft should last virtually forever. A shaft can easily tolerate a one-time force over the endurance level, but fails if that force is applied to the same shaft millions of times or cycles. The revolving shaft of a bandsaw is a good place for applying the compression-tension cycles that cause metal fatigue. It would take only 15 to 20 hours of use to accumulate a million cycles. The greater the excess of force, the lower the number of cycles it would take to cause the failure.

Adequate tension is important for the blade's bandsaws performance, but it is only part of the solution. Increasing the tension cannot make up for improper wheel alignment or the wrong blade choice. If you have to greatly exceed the tension scale setting for good performance, it is a clue that you are doing something wrong. If you do not correct the problem and continue to use excessive tension, you risk the chance of damaging your bandsaw.

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