What TPI Reciprocating Saw Blade Cuts Steel Pipe?

Four answers go around, and they look like they disagree. Makita sells an 8 TPI blade for 2 in pipe. A Milwaukee 14 TPI blade is listed for 3/16 to 1/2 in metal and Schedule 80 pipe. Diablo lists an 8 TPI carbide blade for 3/16 to 9/16 in. And the old shop rule says to keep three teeth in the material. Put the pipe's wall next to each one and they stop fighting. Most of the confusion comes from reading "thick pipe" as big pipe. The blade only cares about the wall.

TPI, wall thickness and schedule

TPI means teeth per inch. It counts the teeth along one inch of the blade's edge. An 8 TPI blade has 8 teeth in each inch, so they sit 1/8 in apart. A 24 TPI blade has teeth 1/24 in apart. Lower TPI means bigger teeth with more room between them.

The wall is the steel between the outside and the inside of the pipe. When a reciprocating saw cuts a pipe, the teeth bite into that ring of steel, not the hollow middle. So the wall is the material the blade has to cut.

Schedule is the name for a wall thickness at a given pipe size. Schedule 40 is the standard wall. Schedule 80 is the thicker, extra strong wall. The size, such as 2 in, is a trade name. A 2 in pipe is 2.375 in across the outside, and its wall is 0.154 in in Schedule 40 or 0.218 in in Schedule 80. Those figures come from Wheatland Tube's tables for ASTM A53 pipe, the common black and galvanized steel pipe.

The three-teeth rule

The rule says at least three teeth should be in the material at all times. United Products, a bandsaw blade supplier, puts the reason plainly. When only one or two teeth touch, each tooth takes a heavy hit as it enters the cut, and teeth can strip off the blade. Spread the load over three or more and each tooth takes less.

In a pipe, the material is the wall. So the count is simple arithmetic:

• Teeth in the wall = wall thickness x TPI
• TPI for three teeth = 3 / wall thickness

United Products is just as plain about the rule's limits. It calls it a guide, "not a perfect mathematical rule". It says thin wall tube "is often a compromise," because the blade enters and leaves the steel over and over. Keep both halves in mind. The rule says which way to lean, and the makers' own ranges show how far they lean.

Worked through: 2 in Schedule 40

Take a length of 2 in Schedule 40 steel pipe. Its wall is 0.154 in. Here is what each blade puts in that wall:

• 8 TPI (Makita E-26191): 0.154 x 8 = 1.2 teeth
• 14 TPI (Milwaukee Torch): 0.154 x 14 = 2.2 teeth
• 18 TPI (Starrett's pick for this wall): 0.154 x 18 = 2.8 teeth
• 24 TPI: 0.154 x 24 = 3.7 teeth

Three teeth needs 3 / 0.154 = 19.5 TPI. So by the rule, 24 TPI passes, 18 TPI comes close, and 14 and 8 TPI fall short.

Now set the makers beside that. Starrett's guide works this exact case. For "2-in. steel tube with a wall thickness of 0.16 in.," it says "the correct TPI is 18." Milwaukee's 14 TPI blade and Diablo's 8 TPI carbide blade are both listed from 3/16 in, which is 0.1875 in. A 0.154 in wall is thinner than where either range starts. Makita's 8 TPI blade is the only one sold for 2 in pipe by name, and that claim comes tied to one machine, covered below.

So for 2 in Schedule 40 on a handheld saw, the answer is 18 to 24 TPI. 18 TPI is the maker's choice for this wall. 24 TPI is the one that meets the three-teeth rule outright.

Teeth in the wall, 1/2 to 4 in pipe

Here is the same arithmetic for every size from 1/2 to 4 in, in both schedules. Walls and outside diameters are Wheatland's nominal figures. The last column is 3 divided by the wall.

Three things stand out.

First, no 8 TPI blade reaches three teeth in any of these walls. The best case is 4 in Schedule 80, at 2.7 teeth. Read as a hard line, the rule would rule out every 8 TPI blade on every pipe here.

Second, 14 TPI reaches three teeth at 2 in Schedule 80 and at 3 in Schedule 40, and in every larger wall in the table. 18 TPI gets there from 1 in Schedule 80 and from 2-1/2 in Schedule 40.

Third, 2 in Schedule 40 and 3/4 in Schedule 80 have the same wall, 0.154 in. A blade that suits one suits the other. Pipe size alone does not tell you which blade to use.

The thinnest walls here, 1/2 and 3/4 in Schedule 40, are under 1/8 in. Starrett's guide gives 24 TPI for 1/8 in steel, and it only lowers TPI as the material gets thicker. So walls under 1/8 in take 24 TPI. Even then, 24 TPI puts 2.6 teeth in a 1/2 in Schedule 40 wall, short of three.

What each maker's range covers

Each blade's listed range, set against the walls above:

The Milwaukee figures come from a retailer's listing, The Power Tool Store, not from Milwaukee's own page. That listing names "Thick Metal (3/16" - 1/2"), Schedule 80 Pipe, Angle Iron." It also gives the blade as bi-metal, 0.042 in thick and 1 in tall. The Diablo range comes from Toolnut's listing, which describes "extreme thick metal cutting applications between 3/16 to 9/16."

Look at the thin end of each range. Milwaukee's 14 TPI blade puts 2.6 teeth in a 3/16 in wall. Diablo's 8 TPI carbide blade puts 1.5. Both makers list their blades below three teeth at the thin end. That is the plainest sign that the three-teeth rule is a guide, not a cutoff, which is what United Products says too. It also means "three teeth" cannot be used to reject a blade inside its own maker's range.

Makita's page names the use and the machine. The E-26191 is for "metal, cast iron and stainless pipes," with "clean, efficient 2" pipe cutting," and it is designed for the 40V max XGT Recipro Pipe Saw with Chain Vise, model GRJ03. It has a .062 in blade body, which Makita calls "thicker" for demanding work. The page gives no wall thickness and no schedule. So it says nothing about a handheld saw on 2 in Schedule 40, and it is not a general rule for one.

Settling the 2 in question

Here is how the four answers line up for 2 in pipe.

• Makita's 8 TPI holds for Makita's pipe saw with its chain vise. It names no wall and no other saw.
• Milwaukee's 14 TPI fits 2 in Schedule 80. Its 0.218 in wall is inside 3/16 to 1/2 in, and it gets 3.1 teeth. It does not fit 2 in Schedule 40, whose wall is under 3/16 in.
• Diablo's 8 TPI carbide starts at the same 3/16 in as the Milwaukee range, so 2 in Schedule 80 is in and 2 in Schedule 40 is out.
• The three-teeth rule asks for about 20 TPI in 2 in Schedule 40. Starrett's 18 TPI is close. 24 TPI meets it.

The answer that survives every source: on a handheld saw, cut 2 in Schedule 40 with 18 to 24 TPI and 2 in Schedule 80 with 14 TPI. The 8 TPI answer is real, but it belongs to one machine.

Why the sides of the pipe are the thin spot

The tooth count above is the worst case, and it helps to see where it happens. A blade cutting down through a pipe meets the wall at a different angle at each depth.

Near the top, the blade runs along the curve of the wall. Just as it breaks into the hollow, it is in about 1.17 in of steel on 2 in Schedule 40. That figure is this site's geometry, from Wheatland's 2.375 in diameter and 0.154 in wall. Lower down, the blade crosses the two side walls almost straight on. There, each wall is only as long as it is thick.

So the start of a cut does not test the blade. The sides do. That is why wall thickness, not diameter, picks the TPI.

Real walls can be thinner than the table

The walls above are nominal. ASTM A53 allows less. Wheatland's A53 data sheet says the "minimum wall thickness at any point shall not be more than 12.5% under nominal wall thickness specified." So a wall can be as thin as 87.5 percent of its nominal figure and still be in spec.

On 2 in Schedule 40, 0.154 x 0.875 = 0.135 in. An 18 TPI blade then puts 2.4 teeth in the wall instead of 2.8. Three teeth would take 22.3 TPI.

The tolerance also moves some pipes across the 3/16 in line where the Milwaukee and Diablo ranges start:

Those three pipes sit near the line. A 14 TPI blade is inside its listed range at their nominal walls, but a thin length of pipe can fall just below it. For them, an 18 TPI blade is the choice that does not depend on which side of the tolerance the pipe landed.

Which blade for which wall

Each row below restates a ruling made above.

The 8 TPI carbide row rests on Diablo's range alone. It puts fewer teeth in the wall than 14 TPI. Diablo's listing says the carbide blade lasts "50 times longer" than standard bi-metal in thick metal from 3/16 to 9/16 in. That is the maker's claim, and this page does not rank the two on cut quality.

Where this answer stops

This page matches a blade's tooth count to a pipe's wall. It does not cover everything that decides a good cut.

• Other pipe. The walls are Wheatland's A53 figures for black and galvanized steel pipe. Stainless pipe, thin wall conduit, copper and cast iron use other wall tables. Makita and Diablo list cast iron and stainless as uses, but this page has no wall figures for them.
• Saw setup. Starrett's guide also covers stroke speed, feed pressure and the orbital setting, and it changes them for stainless. A blade with the right TPI can still be run too fast or pushed too hard. Your saw's manual governs those settings.
• Blade length. Starrett adds 3 in to the cut section to get the shortest blade: 2 in for tip clearance and 1 in for the stroke. On 2 in pipe, 2.375 in across, that comes to about 5.4 in, so a 6 in blade.
• Pipe cutters. Some saws are not reciprocating saws. Milwaukee's 48-40-4062 is a carbide toothed blade made only for its M18 FUEL 1/2 to 1 in steel pipe cutter. Its page lists no TPI, so it is not in the tables.
• Safety. A clamped pipe and a guarded saw are still yours to check. Hold the pipe so it cannot roll or pinch the blade, and wear eye protection against chips. Nothing on this page replaces the saw maker's instructions.

Pipe, blades and the rest of the kit

If you cut pipe often, the other common tool is an angle grinder with a cut-off wheel. Wheel size and guard rules apply there, as in whether a 4-1/2 in cut-off wheel goes on a 5 in grinder. Bonded wheels also age, which cut-off wheel shelf life covers.

Kerf and tooth figures matter on a table saw too, where the check is the blade against the riving knife. That one is worked through in using a thin kerf blade with a riving knife.

Spare blades are steel, and a damp shop rusts the teeth before they cut anything. The humidity steps in rust prevention in tool storage apply to a box of blades. And pipe work often ends at a weld, which brings its own storage numbers in storing 7018 welding rods.

The thirty-second check

1. Find the wall, not the size. 2 in Schedule 40 is 0.154 in. 2 in Schedule 80 is 0.218 in.
2. Wall under 3/16 in: use 18 TPI, or 24 TPI for three teeth in the wall.
3. Wall 3/16 in or more: a 14 TPI bi-metal or an 8 TPI carbide blade is inside its maker's range.
4. Wall near 3/16 in: allow for A53's 12.5 percent tolerance, and go to 18 TPI if the pipe may be thin.
5. To check any wall, multiply it by the TPI. Three or more teeth meets the rule. Below that, check the maker's listed range.