A riving knife on a table saw is a safety device that looks like a thin blade but stays right behind the saw blade. Its main job is to keep the wood you are cutting from pinching back together onto the blade after the cut starts. This simple yet vital table saw safety device prevents dangerous kickback.
The Critical Role of the Riving Knife
Many woodworkers ask about this part. What makes the riving knife function so important? Think about cutting a piece of wood. As the blade slices through, the wood fibers separate. Friction is created. If the wood closes up behind the blade, it grabs the saw teeth. This sudden grab is called kickback. Kickback sends the wood flying back at the operator, which is very dangerous.
The riving knife acts as a constant wedge. It keeps the saw cut, or the kerf, open. This separation prevents the wood from pinching the blade body. It offers crucial blade body support exactly where it is needed most.
Riving Knife vs. Splitter: Are They the Same?
Often, people use the terms interchangeably. Is a table saw splitter the same as a riving knife? In most modern table saws, yes, they are effectively the same thing.
Historically, a splitter was a fixed piece of metal bolted to the saw table, designed to stay in place regardless of the blade size. A riving knife is usually mounted to the arbor assembly or the table saw blade guard assembly. This means the riving knife can be easily raised or lowered with the blade. It also allows for easy removal when making non-through cuts, like dados or rabbets.
- Riving Knife: Typically raises and lowers with the blade.
- Splitter: Can refer to the fixed type or the modern mechanism.
For clarity in modern usage, think of the thin kerf splitter or riving knife as performing the same essential protective duty.
Why You Must Use a Riving Knife
Safety is the number one reason. However, efficiency and cut quality also improve when using this device. A table saw without one is often incomplete or operating unsafely.
Preventing Dangerous Kickback
Kickback is the biggest hazard associated with table saws. It happens fast. A piece of wood pinches the back of the blade. The blade throws the wood toward you with great force. A properly installed riving knife stops this by holding the wood apart. It acts as an anti-kickback table saw feature built right in.
Improving Cut Quality
When wood pinches the blade, it causes vibration and burning. The saw struggles to cut smoothly.
- The cut edge becomes rougher.
- Burn marks appear on the wood.
- The blade may wander slightly.
By keeping the kerf open, the riving knife allows the narrow kerf blade to move freely. This results in cleaner, straighter cuts every time.
Dealing with Different Blade Types
Table saws often use blades of different thicknesses. A standard blade has a thicker body than a thin kerf blade.
- Standard Kerf Blades: Thicker blade body.
- Narrow Kerf Blades: Thinner blade body.
Riving knives must match the blade being used. You need a knife designed for a narrow kerf blade if you are using one. Using the wrong thickness knife can actually cause binding or damage the knife itself. Always match the knife thickness to your blade kerf.
Anatomy of a Riving Knife System
A modern table saw often includes a complete guard assembly. This assembly holds several key safety components.
The Guard Assembly Components
The entire unit usually includes three parts that work together:
- The Riving Knife/Splitter: The primary wedge shape.
- The Blade Guard: The clear plastic shield over the top of the blade.
- Anti-kickback Pawls: Small, sharp teeth that dig into the wood if it tries to move backward.
When setting up your saw, you often choose which safety features to engage. Many pros remove the guard assembly for certain cuts (like non-through cuts), but they usually keep the riving knife installed.
How the Knife Attaches
Attachment methods vary by saw brand and model.
1. Arbor Mount (Most Common)
The riving knife is mounted directly to the arbor or the quill assembly behind the blade. It moves up and down with the blade. This ensures the knife is always the correct distance behind the teeth, regardless of blade height. This is the preferred method for quick adjustments.
2. Guard Mount
In some designs, the riving knife is bolted directly to the clear plastic blade guard. If you remove the guard, the knife comes off too. This is less ideal if you want to keep the knife on for non-through cuts, as you must remember to reinstall it later.
3. Fixed Mounting (Older or Cabinet Saws)
Some large cabinet saws might have a fixed mounting point, sometimes requiring adjustments when changing blade types, though modern designs favor the floating or arbor mount for convenience.
Selecting the Right Riving Knife for Your Saw
Not all riving knives are universal. Using the wrong one can be dangerous or simply ineffective. You must choose the correct table saw accessory for your machine.
Matching Blade Thickness
This is the most crucial factor. Manufacturers make knives specifically for standard kerf blades (usually 1/8 inch thick) and narrow kerf blade systems (often 3/32 inch thick).
| Blade Type | Typical Kerf Thickness | Required Riving Knife |
|---|---|---|
| Standard Blade | 1/8 inch (0.125″) | Standard Riving Knife |
| Thin Kerf Blade | 3/32 inch (0.094″) | Thin Kerf Splitter |
Using a standard knife with a thin kerf blade can cause binding because the knife is too wide for the cut. Always check your blade packaging or measure the blade body thickness before buying a replacement knife.
Matching Saw Model
The mounting mechanism is specific to the saw’s brand and model. A Riving knife for a Delta saw will likely not fit a SawStop or a Grizzly saw without significant modification—modifications that compromise safety. Always buy parts designed for your specific machine.
Material Considerations
Riving knives are generally made from hardened steel. This material ensures durability and resistance to wear as it slices through the wood fibers. Some kits might include interchangeable tips or specialized mounting hardware.
Adjusting and Using the Riving Knife Correctly
Proper setup ensures maximum protection and performance. Incorrect adjustment can negate the knife’s benefits.
Height Adjustment
The riving knife must align correctly with the blade. General best practice dictates the knife tip should sit no more than 1/4 inch below the top of the teeth.
Rule of Thumb: The tip of the riving knife should never be higher than the highest point of the saw teeth.
If the knife is too low, it offers no support when the wood closes up immediately behind the blade teeth. If it is too high, it might interfere with setting the blade depth or contact the wood unnecessarily during the cut.
Removal for Special Cuts
There are times when a riving knife must be removed, or at least lowered significantly:
- Dadoes and Grooves: When cutting wide grooves (like for shelves or joinery), the blade stack is much wider than the knife. The knife must be removed or lowered completely so it doesn’t hit the wood being cut.
- Rabbets (When the blade doesn’t cut through the whole piece): If the cut does not go all the way through the material thickness, the knife might interfere.
Crucial Reminder: Anytime the riving knife is removed, you eliminate a major anti-kickback table saw feature. You must rely entirely on careful technique, keeping the wood tight against the table saw fence, and using push sticks.
Riving Knife Maintenance and Inspection
A dull or damaged riving knife is less effective. Regular inspection is necessary, especially after hard use or if you notice unusual resistance during cuts.
Checking for Damage
Inspect the tip of the knife regularly. Look for:
- Bends or warps in the steel.
- Nicks or chips, especially near the trailing edge.
- Excessive dullness (though knives are not meant to be sharpened like blades, severe wear reduces their effectiveness).
If the knife is noticeably damaged, replace it immediately. It is a relatively inexpensive table saw accessory compared to the cost of an injury or damaged workpiece.
Cleaning
Wood glue, pitch, and sawdust build up on the knife. This residue increases friction, which defeats the purpose of the knife. Clean the knife using a non-solvent cleaner or specialized spray designed to remove pitch. Ensure it is completely dry before reinstalling.
Riving Knives vs. Other Safety Mechanisms
The table saw safety device landscape includes several options. It helps to compare the riving knife to its main counterparts.
The Blade Guard vs. The Riving Knife
The table saw blade guard protects you from touching the blade directly from above. It is excellent passive protection. However, it does nothing to stop the wood from pinching the blade from the back. They work best when used together. The guard protects your hand from above; the knife protects the wood from closing below.
Kickback Pawls
As mentioned, pawls dig into the wood if it tries to move backward toward the operator. They are excellent last-resort measures. The riving knife prevents the event (kickback) from starting by keeping the wood moving forward. The pawls stop the wood if the knife somehow fails or if the wood is lifted off the table.
| Safety Device | Primary Function | When is it Most Effective? |
|---|---|---|
| Riving Knife | Keeps the kerf open; prevents pinching. | During through cuts where wood might close. |
| Blade Guard | Shields the top of the blade from contact. | Constant passive protection during operation. |
| Kickback Pawls | Digs into wood to stop backward movement. | If the wood begins to slide backward. |
To achieve maximum anti-kickback table saw performance, all these devices should be used in conjunction whenever possible.
Advanced Topics: Setups for Different Cuts
Fathoming how the riving knife interacts with various cutting techniques enhances your woodworking safety profile.
Ripping Long Boards
When ripping long boards, maintaining consistent pressure against the table saw fence is key. Even with a knife, if the wood drifts away from the fence mid-cut, the offcut side can twist and bind the blade. The riving knife helps absorb minor variations, but good technique is still required.
Crosscutting
Riving knives are generally not needed or are incompatible with standard crosscut sleds or miter gauges. In crosscutting, the wood piece is supported by the miter gauge or sled, and the offcut piece falls away immediately after the blade passes. There is very little chance for the kerf to close up on the blade body. If you are using a specialized jig that holds the wood extremely tightly against the fence during a crosscut, consult your saw manual regarding knife use.
Using Thin Kerf Blades with Riving Knives
The advent of the narrow kerf blade allowed saw motors to run cooler and required less power. When using these blades, it is vital to use a matching thin kerf splitter. A standard knife will rub against the blade body, causing friction, noise, and potentially heating the blade excessively. Ensure the knife sits perfectly in the cut slot created by the thin blade.
Comprehending the Physics of Binding
Why does the wood bind without the knife? It comes down to blade geometry and friction.
- Blade Teeth Angle: The teeth are angled to pull the wood toward the fence and down onto the table. This is the feed direction.
- Friction Behind the Blade: As the teeth exit the wood, the wood fibers on the exit side want to spring back to their original shape.
- The Pinch: If the wood springs back before the blade body has completely passed, the wood clamps down on the back of the blade.
- The Throw: Because the front edge of the teeth is still moving forward and down, the blade grabs the wood and accelerates it in the direction of the feed—right toward the operator.
The riving knife physically occupies the space created by the blade after the cutting edge passes. It ensures that the wood cannot move back into that space, eliminating the pinch point entirely. This provides essential blade body support against the forces that cause kickback.
Riving Knife Installation Guide (General Steps)
Installation often requires accessing the area directly behind the blade. Always disconnect power to the saw before performing maintenance.
Step 1: Blade Removal
Raise the blade fully. Turn off and unplug the saw. Open the base access panel or blade cover. Use the arbor lock button (if available) and the correct wrench to remove the arbor nut and the saw blade.
Step 2: Accessing the Mount
Depending on your saw, you may need to remove the entire table saw guard assembly first. Locate the mounting bracket for the riving knife.
Step 3: Alignment and Thickness Check
If replacing the knife, ensure the new knife matches the thickness of your current blade setup (standard or thin kerf). Slide the knife onto its mounting post or into the slot.
Step 4: Height Setting
Reinstall the blade. Raise the blade to full cutting height. Adjust the riving knife bracket so that the tip aligns correctly—no more than 1/4 inch below the highest tooth. Tighten the locking screws securely.
Step 5: Testing
Lower the blade. Reinstall the guard assembly if you removed it. Test the raising and lowering mechanism to ensure the knife moves smoothly with the blade without binding on the guard or the arbor housing.
This entire process ensures that your table saw accessory is installed optimally for anti-kickback table saw protection.
Frequently Asked Questions (FAQ) About Riving Knives
Q: Can I remove the riving knife permanently?
A: While you can physically remove it, it is strongly advised against doing so for any standard through-cut operation. Removing it eliminates your primary defense against kickback. Only remove it temporarily for specific cuts like dados, and reinstall it immediately afterward.
Q: Do cheaper table saws include a riving knife?
A: Many budget or jobsite saws include a guard assembly that incorporates a knife or splitter. However, sometimes these units are cheaply made, or the knife is fixed and not easily adjustable for different blade types, making them less effective than those found on higher-end contractor or cabinet saws.
Q: What is the difference between a Riving Knife and a Throat Plate Insert?
A: The throat plate is the flat piece surrounding the blade opening on the table surface. It provides a smooth surface for the wood. The riving knife is the vertical piece positioned behind the blade. They serve different structural and safety purposes.
Q: Is a riving knife required by safety standards?
A: In many jurisdictions and for many certified machines (like those sold in North America), the inclusion of a functional riving knife or splitter that works in tandem with the blade guard is a key safety requirement.
Q: My saw came with a thin splitter, but I use standard blades. What should I do?
A: You must purchase the correct riving knife insert for standard kerf blades. Using a standard blade with a thin splitter means there is a gap between the back of the blade body and the splitter, which allows the wood to pinch the blade, defeating the safety measure.
Q: Why do some professional woodworkers use a zero-clearance insert instead of the knife?
A: Woodworkers sometimes use a zero-clearance insert (which tightly frames the blade body) to achieve extremely clean edges, especially on veneered plywood. When they do this, they must rely on high-quality anti-kickback pawls or use advanced techniques like featherboards to control the wood, as they have removed the primary table saw splitter mechanism. This is considered an advanced technique and significantly raises the risk profile.
Q: Does the riving knife help with blade runout?
A: No. The riving knife does not correct mechanical issues like excessive blade runout (wobble). Runout is corrected by ensuring the arbor, arbor nut, and blade itself are straight and properly seated. The knife deals with wood behavior after the cut is initiated.