A: Blade “tension” is a technical description of how tight the bandsaw blade is for bandsaws including vertical band saws and horizontal band saws. Bandsaw blades have to be stretched tight to work. Bandsaw blades are tensioned by the amount of force per cross-sectional area of the blade, expressed as PSI (pounds per square inch). Two blades of different sizes will require different forces to achieve the same PSI. For example, a ½” x .025 blade requires 312.5 lbs of force to achieve 25,000 PSI. A 1” x .025 blade requires 625 lbs of force to achieve the same 25,000 PSI, twice as much force because the blade has twice the cross-sectional area.
For carbon steel toothed blades (cutting blades) this is typically 15,000 to 25,000 PSI. Slitting type blades typically are tensioned in the range of 12,000 to 20,000 PSI. In general bandsaw blades are never tensioned past 35,000 psi.
Some machines include a type of gauge or marks to set the blade tension on that machine. These marks generally assume a certain size, therefore cross-section, of blades. What these gauges really do is set a force. The correct force for one blade as indicated by the gauge will be half that needed for a blade twice as large
On a machine with screw over spring tensioning, the most common on smaller machines, only really dependable way to set the blade tension is with a blade tension gauge (available from Forrest, Part Number 000654—Blade Tension Gauge). Blade tension meters directly read the tension in the blade. It is also possible to develop rules of thumb for tensioning a blade based on the number of turns of the crank.
After using a blade tensioning gauge on a saw a few times it is possible to get a feel for the correct blade tension. After a “calibration period” using a tension gauge, a skilled operator will not need to use the blade tension gauge every time.
A better way to get the correct blade tension is to use a machine with air pressure blade tensioning. As mentioned before, most machines use a screw sitting on top of a spring to set the blade tension. The tighter you turn the spring the more tension on the blade. An air pressure tension system uses an air cylinder to tighten the blade. The operator sets the air pressure using a machine mounted pressure regulator. The machine manufacturer will provide a chart showing how much blade force is generated by any air pressure, and the blade tension in typical blade sizes. For large blades or cutting applications that require a very specific blade tension this is the best way to set the tension.
Blade manufacturers typically recommend a range of blade tensions for their products. In general, it is desirable to use the lowest blade tension that will provide a satisfactory quality cut. Too little band tension and the blade may not cut straight regardless of workpiece feed speed and pressure. Over tightening the blade will shorten the life of the blade wheel rubber, bearings, and blade.