Hacksaw: Blade TPI, Types and How to Use One

A hacksaw is a hand saw with a thin, fine-toothed blade stretched in a steel frame, used to cut metal bars, pipe, bolts and plastic. Standard blades are 10 or 12 in (250 or 300 mm) long and come with 14, 18, 24 or 32 teeth per inch (TPI). Choose the TPI by the thickness of the metal: fewer, larger teeth for thick or soft material and more, finer teeth for thin sheet and tube, so that at least three teeth touch the work at all times.

Hacksaw blade TPI chart

TPI	Best for	Typical work
14	Soft, thick material	Aluminum bar, copper, brass, plastic pipe
18	General use	Mild steel bar and angle, thicker pipe
24	General steel, thinner sections	Steel pipe, conduit, bolts, 1/8 in plate
32	Thin material	Sheet metal, thin tube, thin angle

The three-teeth rule explains the table. If a tooth spans a thin wall, it hooks and snaps. If you use a fine blade on thick soft metal, the small gullets fill with chips and the blade stops cutting. When two TPI values seem possible, pick the finer one for thin work and the coarser one for thick work.

Types of hacksaw blades

• All-hard blades have fully hardened teeth and body. They cut straight and stay sharp, but they snap if bent or twisted.
• Flexible blades have hardened teeth on a softer body. They bend a little without breaking, which makes them the better choice for beginners and for awkward angles.
• Bi-metal blades have high-speed steel teeth welded to a flexible spring-steel back. They cost more and last longer, especially in stainless and tougher steels.

A wavy tooth set, where the teeth lean left and right in groups, is used on thin material. A raker set, with the teeth set in a repeating left, right and straight pattern, is common on thicker stock.

How to fit and use a hacksaw

1. Pick the blade by the thickness of the metal, using the chart above.
2. Fit the blade with the teeth pointing away from the handle. The saw cuts on the push stroke.
3. Tension the blade until it is tight and does not twist when you flex it. A slack blade wanders and snaps.
4. Clamp the work in a vise with the cut line close to the jaws, so it does not vibrate.
5. Start the cut with a few light strokes at a small nick filed at the edge, so the blade does not jump.
6. Use the full length of the blade at a steady 50 to 60 strokes per minute. Press on the forward stroke and ease off on the return.
7. Keep the blade square to the work. Slow down toward the end so the last section does not tear or snap the blade.

For steel, a drop of cutting oil on the blade reduces heat and wear. For aluminum, wax or oil keeps the soft metal from clogging the teeth.

Common problems

• Broken blades. Usually from too much pressure, a slack blade or twisting the frame. A new blade is wider than a worn one, so it binds in a cut the old blade started; begin a fresh cut instead.
• Teeth stripped off. The TPI is too coarse for the thickness of the metal, so the teeth catch and break.
• Blade wanders. The blade is too slack, or you are cutting at an angle to the clamped work.

When another tool is better

A hacksaw is slow on thick bar, long cuts and hard material. A band saw, an angle grinder with a cut-off wheel or a chop saw with a metal blade is faster; best saw for cutting metal compares them. A reciprocating saw with a metal blade handles pipe and bolts in places a hacksaw frame cannot reach. A hacksaw is the right choice for a few quick cuts, for tight spots and for jobs with no power nearby.

Related guides

• Types of hand saws and their uses
• Coping saw vs scroll saw
• Can a wood bandsaw cut metal?