Find the right blade, right tension, right results

Bandsaw blades are like drill-press speeds: We know we should change them for different tasks, but we usually don't. However a little extra effort to change those blades will reward you with better cuts and longer-lasting equipment. Here's how to best match the blade to the job at hand.

As you shop for blades, it helps to know some of the essential terms:

• Gullet: a chip-clearing gap between the teeth.
• Pitch: the spacing of teeth, expressed in teeth-per-inch (TPI).
• Rake angle: the angle of the tooth face relative to the blade body.

• Set: the pattern of bending teeth to the left or right to create a kerf wide enough to keep wood from pinching the blade body as you cut.

In the first drawing, alternate-set blades spread the work to ease cutting thick stock. Raker teeth cut cleaner by clearing chips better.

In the second drawing, standard blades cut aggressively, while skip-tooth blades clear chips to make smooth cuts. Variable-tooth spacing compromises on both. Hook teeth prove most aggressive, but dull faster.

Next match the blade pitch to the workpiece thickness. The thinner the stock, the greater the TPI you can use. You want at least three teeth in the wood at any one time as the blade cuts, but no more than 12. (To resaw pieces more than 6" wide, just slow the feed rate.) More teeth leave smoother surfaces, but have smaller gullets that inhibit chip clearing.

For general rules on the best TPI for everyday jobs, see the first chart. To match a blade to curved cuts, refer to the second chart. For resawing, install the widest blade that fits your saw as specified in the manual.

Constant tension on an idle bandsaw blade creates stresses that lead to premature wear, vibration, and broken blades. Detension if the saw will sit unused for more than a day.

With too little tension, bandsaw blades will stall in the wood or drift off the cut line. But too much tension stresses the saw, and shortens blade life. You can buy expensive (though accurate) tensioning gauges, but tensioning needn't be that precise. Instead, set the tension one of these three ways:

• The built-in tensioning scale. These typically indicate more than the actual tension, but they're sufficient for most jobs. If you notice blade deflection, try one of the following methods.
• The deflection test. First set the blade tension using the built-in gauge and raise the upper guide as high as it will go. Then stand a square 1⁄8" from the blade, and push the center of the blade with your thumb, as shown. Under moderate pressure, the blade should just touch the square.
• The "flutter" test. With the guide blocks or bearings withdrawn from the blade, tension the blade using the built-in gauge. Turn on the saw and release tension a half-turn at a time until the blade visibly flutters. Now increase the tension until the fluttering just stops; then add a quarter- to a half-turn of the tensioning knob.

With the blade tensioned and the saw unplugged, loosen the upper and lower pairs of guide blocks and back off both thrust bearings. (Spin the blade wheels by hand to center the blade if you've changed blades.)

Place paper spacers between the loosened upper guide blocks or bearings, and press the blocks and spacers against the blade body, shown in photo. Tighten the guides in place while pressing them against the blade, and repeat for the lower guides.

Now advance the upper thrust bearing until the blade just clears it, as shown in photo. Tighten the thrust bearing in position, repeat for the lower thrust bearing, and you're ready to cut.