Router Guide Bushing Setup: Template Routing Done Right

Quick answer

Set up a router guide bushing by matching the bushing OD to your template opening, installing it in a compatible sub-base or adapter, and calculating the offset as (bushing OD minus bit diameter) divided by two. Then cut a test piece to verify the offset before routing your final part. For tight inside corners, plan to square them with a chisel after routing.

How the bushing and template interact

A router guide bushing, also called a template guide, is a metal collar that mounts to the router sub-base and rides along the edge of a template or pattern. The bit protrudes through the center of the bushing, and the bushing's outside diameter controls how far the cutting edge sits from the template edge. This is different from a bearing-guided bit, where the bearing sits directly on the bit shank and follows the workpiece or template. With a bushing, the template must be offset from the desired cut by a fixed distance, and that distance changes if you swap the bushing or the bit.

Bushings are commonly sized by outside diameter and inside diameter, and they must match your router sub-base or adapter. If the bushing does not seat flush, it can shift mid-cut and ruin the part. Always check that the bushing is fully seated and the retaining ring or screws are tight before you start the router.

Calculating the offset correctly

The offset is the distance between the bushing's outside edge and the bit's cutting edge. Use this formula: offset = (bushing outside diameter − bit diameter) ÷ 2. For example, a 1-1/8′′ outside diameter bushing with a 1/2′′ bit gives an offset of (1.125 − 0.5) ÷ 2 = 0.3125′′, or 5/16′′. That means the template must be 5/16′′ larger than the finished part on every edge that the bushing follows.

If you are using a bushing with a different outside diameter, recalculate. Never assume the offset stays the same when you change bits or bushings. Write the offset on the template or a piece of tape on the router so you do not forget it between setups.

Step-by-step setup and cutting process

Follow this order to avoid rework. First, choose a bushing that fits your router's sub-base or adapter and matches the template opening you plan to use. Second, install the bit and set the depth of cut. Third, calculate the offset and adjust your template size or position accordingly. Fourth, make a test cut on scrap material to verify the offset and the bushing's tracking. Fifth, rout the final part in light passes, keeping the bushing pressed firmly against the template. Finally, inspect the cut and square any rounded inside corners if needed.

• Common mistake: forcing the bushing against the template too hard, which can burn the template edge or cause the bushing to tilt.
• Checkpoint: after the test cut, measure the distance from the template edge to the cut edge. It should match your calculated offset within a few thousandths of an inch.

When to use a bushing instead of a bearing

Bushings excel when you need to follow a template with complex curves or when you want to use a straight bit for pattern routing. They also let you use the same template with different bits by changing the bushing and recalculating the offset. Bearing-guided bits are simpler for edge profiling or flush trimming because the bearing is built into the bit and no offset calculation is needed. However, bearings can be less versatile for deep template work where the bearing might not reach the template surface.

If you already own a set of bushings, you can adapt many standard routers with the right sub-base. If you are starting fresh, consider which type of routing you do most. For template routing with a bushing, you will need a template material that is thick enough to guide the bushing without flexing, such as 1/2′′ MDF or plywood.

Squaring inside corners after routing

A round bit leaves rounded inside corners. If your project requires square corners, such as for a hinge mortise or a square cutout, you can square them with a chisel after routing. A square corner chisel is designed for this task: it has a square cutting blade that matches the corner radius left by common router bits. To use it, align the chisel in the corner and strike it with a mallet. The hardened steel blade shears the wood fibers cleanly. This step is often overlooked but makes a big difference in fit and finish for joinery and hardware installation.

Bushing setup checklist

1. Match bushing to sub-base: Ensure the bushing's outside diameter and mounting style fit your router's sub-base or adapter. A loose bushing will shift during the cut. Checkpoint: the bushing should sit flush with no wobble when the retaining ring is tight.
2. Calculate offset: Use offset = (bushing OD − bit diameter) ÷ 2. Write it down and adjust your template size accordingly. Checkpoint: verify the math with a test cut on scrap before routing the final part.
3. Set bit depth and install: Install the bit, set the depth of cut, and double-check that the bushing is fully seated and the bit spins freely inside it without contact. Checkpoint: spin the router by hand (unplugged) to confirm no interference.
4. Make a test cut: Rout a scrap piece using the same template and bushing setup. Measure the offset and adjust the template if needed. Checkpoint: the cut edge should match your intended offset within a few thousandths.
5. Rout the final part: Use light passes, keep the bushing pressed against the template, and maintain a steady feed rate to avoid burning. Checkpoint: stop if you hear chattering or feel resistance—the bushing may be tilting.
6. Square inside corners if needed: For square corners, use a square corner chisel aligned in the corner and strike with a mallet. Checkpoint: test the chisel on scrap to avoid tear-out on the final part.

Parts that support accurate bushing work

• 11/16″ Router Bit Bearing x 3/16″ID – Whiteside B14: 11/16′′ outside diameter, 3/16′′ inside diameter replacement router bit bearing. If you use bearing-guided bits alongside bushing setups, a worn bearing can cause the bit to wander. This replacement bearing restores precise guidance for 3/16′′ shank bits.
• 1-1/8″ Router Bit Bearing x 1/2″ID – Whiteside B11: 1-1/8′′ outside diameter, 1/2′′ inside diameter replacement bearing. A common size for 1/2′′ shank pattern bits. Keeping a spare on hand prevents downtime when a bearing seizes or develops play.
• Square Corner Chisel – Whiteside 9600: Square corner chisel with 3/8′′ square hardened steel cutting blade, made by Whiteside. Align in corner and strike with a mallet. After routing with a bushing and round bit, this chisel squares the rounded inside corners for a clean, professional fit in joinery and hardware recesses.