How to choose the right bandsaw blade TPI

TPI stands for teeth per inch, the number of tooth points along 25.4mm of band. The right pitch keeps a minimum of 3 teeth in the workpiece at any moment, ideally 6 to 12 and never more than about 24. Thin sections therefore take fine pitches so individual teeth cannot snag, and thick sections take coarse pitches so the gullets can carry the chips out of the cut.

What TPI actually measures

TPI is counted from tooth tip to tooth tip along one inch of the band. It describes more than spacing: as pitch gets coarser the teeth get larger and the gullets, the curved pockets between the teeth, get deeper. The gullet is the blade's wheelbarrow. Each tooth carries its chip in its gullet for the full depth of the cut and only empties it when it exits the workpiece, so choosing a pitch is really deciding how much chip each tooth must carry and how far.

Constant and variable pitch

A constant pitch blade spaces every tooth identically: 4 TPI, 6 TPI, 10 TPI and so on. It is predictable, straightforward to sharpen and the normal choice for wood and for repetitive cutting of one section size.

A variable pitch blade, written as two numbers such as 4/6 or 10/14, varies the tooth spacing and gullet size in a repeating pattern along the band. The changing spacing breaks up the rhythmic vibration that a constant pitch can set up in metal, so the cut runs quieter and smoother, and the mix of tooth sizes lets one blade cover a spread of section sizes. That is why variable pitch is the default on bi-metal blades for mixed fabrication work.

The three-teeth rule

The rule of thumb that governs everything else: keep at least 3 teeth in the workpiece at all times, ideally 6 to 12 and no more than about 24.

With fewer than 3, individual teeth can straddle the work or hook an edge, which is exactly how teeth get stripped off. Tube, angle and other thin walls are the classic case, because the blade enters and leaves a thin section repeatedly on every pass. With more than about 24, each gullet is so small relative to the depth of cut that it packs full of chip before the tooth exits. The blade then rubs instead of cutting, heat climbs and the feed stalls.

For solid sections the arithmetic is direct: teeth in the cut equals TPI multiplied by the section thickness in inches. A 25mm bar is roughly 1 inch, so a 6 TPI blade puts about 6 teeth in the cut, comfortably inside the ideal band. For tube and hollow sections the number that matters is the wall thickness, not the outside diameter, because the wall is what each tooth actually passes through.

Fine versus coarse: the trade

Fine pitches buy surface finish and safety in thin material. More teeth share the work, each takes a smaller bite and the cut face comes out smoother. The cost is chip room: small gullets fill quickly, so deep cuts run slowly and can clog.

Coarse pitches buy chip clearance. Big gullets swallow the long chips a deep cut produces, so the blade takes feed pressure and keeps cutting instead of rubbing. The cost is a rougher finish and real risk in thin material, where a large tooth can catch a wall and strip.

Neither end is better. The section in front of the blade decides.

Starting points by section thickness

The pitches below are workshop starting points for general metal cutting, not a specification. The selection chart from the blade manufacturer and your machine manual take precedence, and the material shifts the choice too: gummy, chip-heavy materials push it a step coarser.

Wood follows the same logic but lands much coarser. A deep rip or resaw produces an enormous volume of chip per tooth, which is why wood blades run open pitches with generous gullets, and why the fine pitch that flatters a shallow curve cut will choke in a 200mm resaw.

Section thickness drives the choice

If your work is one section all day, pick the pitch for that section and enjoy the consistency. Most workshops cut a mix, and there the honest advice is to choose for the thinnest section you cut regularly, because a too-coarse blade strips teeth on thin walls while a too-fine blade merely cuts thick stock slowly. A variable pitch stretches one blade across the middle of the range, and a shop that regularly cuts both thin tube and big solids will be happier with two blades than one compromise.

Interrupted cuts deserve a mention: bundles, angle stacked on edge and structural profiles hammer the blade with entries and exits, and a step finer than the thickness alone suggests keeps the impact per tooth down.

Pitch is half the story

A correct pitch still fails at the wrong band speed or feed. Fine powdery dust where there should be chips usually means the pitch is too fine for the section or the feed too light, and the fix is covered in our speed and feed guide. If you would rather start from the machine and material and let the catalogue narrow itself, the blade finder asks for exactly those and returns the constructions and pitches that fit.