Can You Use a Thin Kerf Blade With a Riving Knife?

Two answers go around: one says a thin kerf blade will bind on a riving knife, and the other says any blade works. Both miss the point, because a riving knife has a window and the blade has to land in it. The knife must be thicker than the blade's steel plate and thinner than the cut its teeth make. Every saw checked here has a knife thinner than 3/32 in, so it is already sized for a thin kerf blade. The blades that bind are the few sold as thin kerf that cut narrower than the window.

The rule is two numbers

A blade has two widths that matter for a riving knife. The kerf is the width of the cut, set by the carbide teeth, and the plate (also called the body) is the steel disc the teeth sit on. The teeth stick out past the plate on both sides, so the kerf is always the wider of the two.

The knife rides in the cut behind the blade: if it is wider than the kerf, the wood runs into it, and if it is thinner than the plate, the cut can close up behind the blade. DeWalt's manual puts both sides in one sentence: "the body of the saw blade must be thinner than the thickness of the riving knife and the cutting width of the saw blade must be wider than the thickness of the riving knife." Skil's manual uses the same words.

Fine Woodworking's 2009 answer gives only one side: "The riving knife should be as thin as or thinner than the kerf of the blade you plan to use." That is true, but it stops there and never mentions the plate, which is part of why the question keeps coming back. A reader who checks only the kerf can pick a knife that is too thin, and one who checks nothing assumes every blade is fine.

What each saw's manual allows

Here is each maker's window, taken from its own manual. The window width column is the minimum kerf less the maximum plate, which is how much room a blade has to land in.

A few notes on reading this table:

• DeWalt prints the limits on a label shown in the manual: "0.087" (2.2 mm) THICK RIVING KNIFE. ONLY USE FOR 10" (254 mm) Ø BLADE WITH 0.094" (2.4 mm) MIN. KERF WIDTH AND 0.079" (2.00 mm) MAX. BODY THICKNESS." The forum figures of 0.094 and 0.079 in match it.
• Bosch and Skil print the same pair of numbers. Bosch says "You must select a blade with a kerf width of .092" or more and a plate (body) thickness .088" or less." Skil's figure adds the knife at .090 in, while Bosch's page shows the same layout with no knife figure, so the table leaves it blank.
• SawStop's manuals do not give one rule. The compact saw says "Do NOT use a blade with a kerf less than 3/32" (3 mm)", though 3/32 in is 2.4 mm, not 3 mm, and the cabinet saw says 2.35 mm. The Jobsite Saw Pro figures come from the European 230 V manual, the only JSS manual read here.
• Makita lists three figures as "Riving knife-related specs": blade body 1.8 mm, knife 2.3 mm and kerf width 2.6 mm. They are single values rather than a minimum and maximum, and Makita prints "3/32"" beside both 2.3 mm and 2.6 mm, so use the millimeters.

The windows are not the same size: DeWalt and the SawStop compact saw leave about 0.015 in between their limits, while Bosch and Skil leave only .004 in, so a blade has far less room to miss on those two saws.

Fifteen thin kerf blades, kerf and plate

All the blades below are 10 in, and the figures come from Diablo's and Freud's spec pages and from Forrest's own listings.

Two things stand out in this table. First, the plates hardly vary: eleven of the thirteen blades with a listed plate use .071 in, which sits under every maximum in the saw table. Second, the kerfs do vary, from .080 to .098 in, so for thin kerf blades on these saws the kerf decides the answer almost every time.

Blade against saw: the check

Set each kerf against each saw's minimum, and a blade passes if its kerf is at or above the minimum and its plate is at or below the maximum.

The Forrest row needs a word: Forrest lists the kerf as 3/32 in, which is 0.0938 in as a decimal, a hair under DeWalt's printed 0.094 in. Shops round 3/32 in to .094 in all the time, but DeWalt's label gives no rounding rule, and Forrest does not list a plate either, so measure this blade before you rely on it.

The .087 in Diablo blades fail twice on the European JSS Pro, because their kerf is under its 0.093 in floor and their .063 in plate is under its 0.071 in minimum. That manual is the only one here with a lower limit on the plate.

Makita: one set of numbers, not a window

Makita's 2705 manual is the odd one out, because it lists a knife of 2.3 mm (0.091 in), a blade body of 1.8 mm (0.071 in) and a kerf of 2.6 mm (0.102 in), the same kerf as the blade Bosch supplies with the 4100. No blade in the table above reaches 2.6 mm.

Makita does not call 2.6 mm a minimum, so read it with the rule instead: the knife has to be thinner than the kerf. Here is how the blades clear the 2.3 mm knife:

A .091 in Freud clears the Makita knife by four ten-thousandths of an inch, which is not a gap anyone can count on. On a 2705, the figures Makita prints describe a blade of about .102 in kerf on a .071 in plate, and the nearest in these tables are Diablo's .098 in blades.

Why the minimum sits above the knife

If the rule is only "kerf wider than the knife", why not set the minimum kerf equal to the knife? Because then the knife would touch both walls of the cut, so the makers leave a gap:

The plate side works the same way: DeWalt's 0.079 in maximum plate is 0.008 in under its knife, and Skil's .088 in is .002 in under its .090 in knife.

Bosch and Skil name the risk on each side of the window. On the kerf side, "Extra thin kerf saw blades (less than .092") may cause the workpiece to bind." On the plate side, Skil warns that with a plate over .088 in, "the riving knife / splitter would not properly serve" its purpose of helping to reduce kickback, and Bosch says the same of its knife. Each edge of the window guards against a different failure.

SawStop adds a reason no other maker gives, because its brake stops the blade by force. The compact saw manual says blades "with kerfs much thinner than 3/32 inch should not be used because those blades might not be strong enough to withstand the force applied by the brake when it activates." So on a SawStop, a very thin blade fails a second test that has nothing to do with the knife.

Checking a blade the makers do not list

Some blades print only the kerf, and some print nothing; Forrest's listings give the kerf for the Woodworker II but no plate. DeWalt's manual gives a four step check that works for any blade:

1. Measure the body thickness of the blade.
2. Make a shallow cut in scrap and measure the width of the cut.
3. Pick the knife that fits between those two numbers.
4. Slide the knife through the shallow cut, where it "should not bind or drag."

Calipers that read to 0.001 in are the right tool, and the plate should be measured on bare steel, away from the teeth. The cut in step 2 is a better kerf figure than the label, because it is what the knife will actually see, and if the measured kerf is close to your knife, step 4 settles it. How far you can trust a reading depends on the tool, the same way a tape measure has an accuracy class, as covered in what Class II means on a tape measure.

Watch for one trap with stiffeners, the metal plates sometimes clamped to the side of a thin blade. Skil says not to use them on both sides because that "will prevent the blade from being properly aligned with the riving knife." Skil allows one stiffener, on the outside of the blade only. Forrest "strongly" recommends one when ripping hardwood with its .080 in ultra thin blade, but that blade fails every saw here on kerf anyway.

SawStop also notes that on its cabinet saw, a thin kerf blade may need "one or more shims" to center the spreader in the cut, so a knife of the right thickness can still sit off center.

Where this answer stops applying

• Other saws. The windows above come from the DeWalt DWE7491, Bosch 4100, Skil TS6307, SawStop CTS, PCS and JSS Pro, and Makita 2705 manuals. Other saws, and other versions of these manuals, can print different figures, and the label on your knife and your manual govern.
• Other knives. Fine Woodworking notes that "most tablesaws equipped with riving knives offer a thin-kerf knife as either standard equipment or as an accessory." Fit a different knife and the window moves with it.
• Full kerf blades. Freud's full kerf P410 is .126 in on a .098 in plate, and that plate is thicker than DeWalt's 0.079 in limit, Bosch's .088 in limit and SawStop's 0.090 in knife. A thicker blade is not safer by default, so check its plate the same way.
• Miter saws. These have no riving knife, but they have kerf and plate limits of their own, such as the 0.100 in maximum plate in Bosch's GCM12SD manual. See whether a 10 in blade goes on a 12 in miter saw for those limits.
• Cut quality and power. This page checks fit only. Whether a thin kerf blade cuts better or worse on a given saw is not a published figure, and it is not settled here.

Storing blades with their numbers

Once you know which blades fit which saw, write it down where you keep them. Mark the kerf and plate on each blade's sleeve or on the rack, so the check takes seconds the next time. For hanging blades, French cleats, pegboard, slatwall and track walls compares what each holds. The carbide is brazed to a steel plate, and steel rusts in a damp garage, so the humidity steps in rust prevention in tool storage apply to spare blades as well.

The same logic runs through other swaps on this site. A smaller accessory can pass one check and fail another, as with a 4-1/2 in cut-off wheel on a 5 in grinder. And if the saw is a 15 A jobsite model, sharing its circuit with a dust collector has its own numbers.

The thirty-second check

1. Find your knife's limits, which are printed on the knife or in the manual: 0.094 in kerf and 0.079 in plate on the DWE7491, .092 and .088 in on the Bosch 4100 and Skil TS6307, 3/32 in kerf on the SawStop CTS.
2. Find the blade's kerf and plate, which are printed on the blade, on the box or on the maker's spec page.
3. Kerf at or above the minimum, plate at or below the maximum: it fits.
4. Kerf of .091 in or less: it fails every minimum printed here.
5. No figure listed: measure the plate, make a shallow cut in scrap, measure that, and slide the knife through it.