To cut a circle with a router, build a simple circle jig (also called a trammel): a straight strip of plywood screwed to your router’s base plate, with a pivot pin at one end. Measure from the pivot pin to the cutting edge of the bit to set your radius, drill a small pivot hole at the center of your workpiece, then rout the circle in shallow passes of 1/8 to 1/4 inch, moving counterclockwise around an outside edge. The jig costs almost nothing, takes about 20 minutes to make, and cuts circles from a few inches to several feet across — far cleaner and more accurate than a jigsaw.
A perfect circle is one of those woodworking jobs that looks easy until you try it freehand. A jigsaw wanders, a bandsaw leaves a rough edge that needs hours of sanding, and a compass and a steady hand only get you a pencil line, not a cut. A router with a circle jig is the tool for this job: the pivot pin locks the radius, the bit follows the same path on every pass, and the edge comes off the tool smooth enough to finish with light sanding. This guide covers the full method — building the jig, setting the radius correctly (the step most people get wrong), cutting inside and outside circles, small circles, router-table circles, and the mistakes that ruin an otherwise good cut.
Why a Router Beats a Jigsaw for Circles
A jigsaw is fine for rough work, but it has three problems on a circle: the narrow blade flexes and drifts, the cut edge is rough and needs heavy sanding, and the blade can wander off the line on curves, especially in thick stock. A router solves all three. The bit is rigid, the cut edge is clean and square, and the jig fixes the radius so the circle is geometrically true — every point on the edge is exactly the same distance from the center.
The trade-off is setup time. A jigsaw needs no jig; a router circle cut needs a trammel arm and a pivot hole. But once the jig exists, every circle after the first takes minutes, and the results are repeatable: the same jig cuts a 12-inch tabletop, a 24-inch lazy Susan, and a 6-inch speaker hole with nothing more than a different pivot hole.
| Tool | Edge quality | Accuracy | Best for |
|---|---|---|---|
| Router + circle jig | Clean, square, nearly finish-ready | Exact radius, repeatable | Tabletops, speaker holes, rings, round signs |
| Jigsaw | Rough, needs sanding | Drifts on curves | Rough cutouts, quick one-offs |
| Bandsaw | Fair, needs sanding | Good on outside curves only | Rough-shaping round blanks |
| Hole saw / Forstner bit | Clean | Fixed sizes only | Small holes up to about 6 inches |
| Router table + swing arm | Clean, square | Exact radius | Small to medium round panels |
What You Need
Most of this is already in a woodworker’s shop. The jig itself is scrap material.
| Item | Notes |
|---|---|
| Plunge or fixed-base router | Either works; a plunge router is easier for starting inside cuts |
| 1/4-inch or 1/2-inch straight bit | 1/2-inch shank preferred for stability; spiral up-cut bit for cleaner cuts in plywood and MDF |
| Scrap plywood or hardboard, 1/4 to 1/2 inch thick | For the jig arm; about 6 inches longer than your largest radius |
| 1/4-inch dowel, nail, or bolt | Pivot pin, matched to the pivot hole you drill |
| Drill + 1/4-inch bit | For the pivot hole in the workpiece |
| Double-sided tape + spoilboard | Holds the workpiece and protects the bench |
| Clamps | To hold the spoilboard to the bench |
| Safety gear | Safety glasses, hearing protection, dust mask |
| Measuring tape, pencil, square | For layout |
Method 1: Build a Simple Circle Jig (Trammel)
This is the core method, and it handles most circles — from about 6 inches up to several feet across. The jig is a flat arm: the router bolts to one end, a pivot pin sticks out of the other, and the distance between the pin and the bit is the radius.
Step 1: Remove the base plate
Unscrew the router’s plastic base plate (also called the sub-base) and set it aside. You will use it as a template for the jig.
Step 2: Trace the base plate onto the jig arm
Lay the base plate on one end of your plywood strip and trace around it, marking the screw holes and the bit opening. The strip should be the same width as the base plate and long enough to reach from the bit to your largest radius plus about 6 inches of spare length.
Step 3: Drill the bit opening and screw holes
Drill a clearance hole for the router bit at the traced bit location — a 1-3/8-inch Forstner bit works well for this. Drill the screw holes to match the base plate, countersinking them from the bottom so the screw heads sit flush and do not scratch the workpiece.
Step 4: Attach the jig to the router
Bolt the jig arm to the router in place of the base plate. The router must sit flat on the arm with the bit centered in the clearance opening. If the arm flexes, use thicker plywood or add a second layer.
Step 5: Mark and drill the pivot hole
This is the step that decides whether your circle comes out the right size. Measure from the pivot point to the cutting edge of the bit — not the center of the bit. For an outside cut (a round disc), measure to the inside edge of the bit, the edge nearest the pivot. For an inside cut (a round hole), measure to the outside edge of the bit. Drill a 1/4-inch hole through the arm at that mark and push a short dowel or nail through it as the pivot pin. The pin should stick out about 1/4 inch below the arm.
Step 6: Mark the center and drill the pivot hole in the workpiece
Find the center of your circle on the workpiece and drill a 1/4-inch hole there, about 1/4 inch deep — it does not need to go all the way through unless the center will be visible in the finished piece. If the center hole would show in the final project, drill it from the back face instead, or fill it later with a matching plug.
Step 7: Cut in shallow passes
Set the router on the workpiece with the pivot pin in the center hole. Set the bit depth so it cuts only 1/8 to 1/4 inch on the first pass. Turn the router on, let it reach full speed, and sweep it smoothly around the pivot in a full circle. Lower the bit another 1/8 to 1/4 inch and repeat. Keep going until you cut through. Never try to cut through thick stock in one pass — the bit will chatter, burn, and can grab the router out of your hands.
Getting the Radius Right: The Bit-Diameter Trap
The most common mistake in circle routing is measuring to the center of the bit instead of its cutting edge. That error makes every circle off by half the bit diameter — 1/8 inch with a 1/4-inch bit, 1/4 inch with a 1/2-inch bit. On a speaker hole or a ring joint, that is enough to ruin the fit.
| What you are cutting | Measure pivot to… | Formula (R = wanted radius, d = bit diameter) |
|---|---|---|
| Outside of a disc (round tabletop) | Inside edge of the bit | Pivot-to-bit-center = R − d/2 |
| Inside of a hole (speaker cutout) | Outside edge of the bit | Pivot-to-bit-center = R + d/2 |
| Circular groove (no through cut) | Center of the bit | Pivot-to-bit-center = R |
A worked example makes this concrete. You want an 18-inch-diameter disc — a 9-inch radius — using a 1/4-inch straight bit. The bit is 1/8 inch from center to edge, so you mark the pivot hole 8-7/8 inches from the center of the bit. The outer edge of the bit then lands exactly 9 inches from the pivot. If you measured 9 inches to the bit center instead, the disc would come out 18-1/4 inches across.
Always test on scrap first when the finished size is critical. Cut a test circle, measure it, and adjust the pivot hole before touching your real workpiece. A second pivot hole in the jig arm costs nothing; a ruined tabletop costs a lot.
Method 2: Small Circles (Under 6 Inches)
A standard trammel arm cannot cut very small circles, because the pivot pin would have to sit almost underneath the router base — the minimum diameter is roughly the width of the router base itself. For small circles, put the pivot point under the base instead of at the end of an arm.
The simplest version is a clear acrylic or plywood base plate with a pivot pin screwed through it close to the bit, plus two guide rods that slide through the router’s fence-rod holes so you can adjust the radius. Commercial versions of this idea, such as the Trend N-COMPASS, cut circles from about 1 inch to 8 inches in diameter. The DIY version works the same way: drill the pivot hole in the workpiece, set the pin-to-bit distance to the radius, and rout in light passes.
Two things matter more on small circles than on large ones. First, the pivot pin must be exactly vertical and snug — a wobbling pin on a 2-inch circle is a visible error, while the same wobble on a 24-inch circle is invisible. Second, take even lighter passes, about 1/16 to 1/8 inch, because the bit is cutting a tight curve and the load on it is higher.
Method 3: Circles on the Router Table
If the workpiece is small enough to handle safely, the router table gives you the cleanest circles of all, because the router is fixed and you rotate the workpiece instead of the tool. Build a simple swing-arm jig: an auxiliary tabletop that sits over the router table, a swing arm pivoted on a bolt, and a stop that limits the arm’s travel to set the diameter.
Drill a small centered hole in the rough-shaped workpiece, drop it over the pivot pin in the swing arm, and set a straight bit — a spiral up-cut bit works well here — to just kiss the edge. Turn the router on, swing the arm toward the bit until it hits the stop, then rotate the workpiece slowly counterclockwise. Sneak up on the final diameter in small steps, moving the stop back a little between passes. This method is excellent for round panels, lazy Susans, and small tabletops, and it also makes perfect dowels by the same principle.
Method 4: Oversized Holes (Bigger Than Your Largest Bit)
Sometimes you need a hole bigger than any Forstner bit or hole saw you own, but you do not want to build a trammel. The rabbeting-bit method works: drill the largest hole you can with a Forstner bit or hole saw, then alternate a rabbeting bit and a flush-trim bit to enlarge it step by step. The rabbeting bit cuts a ledge wider than the hole; the flush-trim bit, riding on that ledge, trims the edge straight. Repeat until you reach the diameter you want. A rabbeting bit set with interchangeable bearings lets you step the diameter in controlled increments — with a 1/2-inch-shank bit you can take about 1/2 inch per pass, and with a 1/4-inch shank about 1/4 inch.
This method is slower than a trammel, but it needs no jig at all, and it is the best option when the hole must be an exact, measurable size and you already own the bits.
Cutting Technique: Direction, Depth, and Feed Rate
Direction is the safety-critical detail, and it flips depending on whether you are cutting the outside or the inside of a circle.
| Cut | Handheld router direction | Why |
|---|---|---|
| Outside edge (disc) | Counterclockwise | Bit cuts against its rotation — a conventional cut, stable and controlled |
| Inside edge (hole) | Clockwise | Same rule, mirrored: the bit still cuts against its rotation |
| Router table (workpiece rotates) | Counterclockwise | Workpiece moves against the bit’s rotation |
Move the router against the bit’s rotation and the bit pulls itself into the cut; move with the rotation — a climb cut — and the bit can grab and throw the router. On an outside edge, a climb cut feels like the router is trying to run away from you. Keep the feed rate steady and never let the router sit still in one spot: a lingering bit burns the wood, and a burn mark on a circle’s edge is hard to sand out because the edge is the finished surface.
Depth per pass depends on the bit and the material, but the safe rule is 1/4 inch maximum, and 1/8 inch for hardwoods, thick stock, or bits smaller than 3/8 inch. A 3/4-inch plywood tabletop takes three or four passes; a 1-1/2-inch solid-wood top takes six or more. That sounds slow, but each pass takes under a minute, and the alternative — one deep pass — risks chatter, tear-out, a burnt edge, or a broken bit.
Material Settings: What Changes With the Wood
Different materials cut differently, and the bit and pass depth should change with them.
| Material | Best bit | Pass depth | Notes |
|---|---|---|---|
| Softwood (pine, cedar) | 1/2-inch straight or spiral up-cut | 1/4 inch | Cuts easily; watch for tear-out on the exit side — use a spoilboard |
| Hardwood (oak, maple, walnut) | 1/2-inch spiral up-cut | 1/8 inch | Slower feed, more passes; burns easily if you linger |
| Plywood | Spiral up-cut | 1/8 to 1/4 inch | Score the cut line with a knife first to reduce face-veneer splintering |
| MDF | Straight or spiral up-cut | 1/4 inch | Cuts cleanly but makes heavy fine dust — wear a mask and use extraction |
| Acrylic / plastic sheet | Straight bit, single-flute if available | 1/8 inch | Keep the feed moving to avoid melting; a sharp bit is essential |
| Melamine / laminate | Spiral down-cut | 1/8 inch | Down-cut bit pushes chips down and keeps the surface from chipping |
Troubleshooting: When the Circle Comes Out Wrong
Most circle-routing problems have one of five causes, and all of them are fixable before the next pass.
| Problem | Likely cause | Fix |
|---|---|---|
| Burn marks on the edge | Bit lingered in one spot, or pass too deep | Keep moving steadily; take lighter passes; check the bit is sharp |
| Circle is too big or too small | Measured to bit center instead of cutting edge | Re-measure pivot to the correct edge (see radius table above); test on scrap |
| Wavy or flat spots on the edge | Pivot pin loose, or arm flexed during the cut | Tighten the pivot fit; use thicker arm material; keep the arm flat on the workpiece |
| Tear-out on the edge | Cutting against the grain on solid wood, or dull bit | Take a light final climb pass only if experienced; otherwise use a sharp spiral bit and a spoilboard |
| Router jumps or grabs | Climb cutting, or pass too deep | Check direction (counterclockwise outside, clockwise inside); reduce depth per pass |
| Center hole visible in finished piece | Pivot hole drilled through the show face | Drill from the back face, or plug the hole with a matching dowel and sand flush |
| Rough, fuzzy edge | Dull bit, or wrong bit for the material | Switch to a sharp spiral bit; sand with 120 then 220 grit, always with the grain direction of the curve |
Safety: The Rules That Matter
A router is one of the loudest, fastest-spinning tools in the shop, and circle routing puts your hands close to the bit while the tool moves in a curve. The rules are simple and non-negotiable: wear safety glasses and hearing protection every time; unplug the router before changing bits or adjusting the jig; keep the power cord routed toward the center of the circle so it cannot catch on the workpiece or wrap around the jig; clamp the spoilboard and workpiece firmly so nothing shifts mid-cut; and never reach across a spinning bit to adjust the jig.
Check the pivot pin before every pass. If the pin works loose, the radius changes mid-cut and the circle is ruined — and a loose pivot can let the router swing free. If the workpiece is small, keep your hands on the router handles, not on the workpiece edge. And always let the bit reach full speed before it touches the wood, and let it stop completely before you lift the router off the jig.
Frequently Asked Questions
Can I cut a circle with a router without a jig?
You can, using a template and a flush-trim bit: cut a rough circle slightly oversize with a jigsaw, screw a perfect circular template on top, and trim to the template. But the template itself has to come from somewhere — usually a circle jig. For a one-off circle, the template method works; for repeated circles, build the trammel.
What is the smallest circle I can cut with a router?
With a standard trammel arm, about 6 inches in diameter — the pivot cannot get closer to the bit than the router base allows. With a pivot-under-the-base jig, you can cut circles down to about 1 inch. Below that, use a Forstner bit or a hole saw instead.
What is the largest circle I can cut?
As large as your jig arm. A 24-inch arm cuts a 48-inch-diameter circle, and longer arms cut larger ones. The practical limit is keeping the arm rigid and flat — beyond about 4 feet, the arm flexes and the circle goes oval. For very large circles, use a thicker arm or a second support.
Should I use a plunge router or a fixed-base router?
Both work. A plunge router is easier for inside cuts because you can start the bit above the wood and plunge in at the cut line. A fixed-base router needs a starting hole or a tilted entry. For outside cuts on a disc, either is fine.
What bit should I use to cut circles in plywood?
A 1/2-inch spiral up-cut bit is the best all-round choice: it clears chips upward, leaves a clean edge, and handles plywood’s glue lines without burning. A straight bit also works and costs less, but it leaves a slightly rougher edge in plywood.
Why does my router burn the wood when cutting circles?
Burning comes from heat, and heat comes from the bit spinning in one place too long. Keep the router moving at a steady pace, take shallower passes, and check that the bit is sharp. A dull bit rubs instead of cutting and burns almost immediately, especially in hardwood.
How do I cut a circle in the middle of a board?
Drill the pivot hole at the center, use a plunge router, and start with the bit above the wood. Plunge in at the cut line and sweep around. The center waste piece will drop out on the final pass, so support it from below with tape or a spoilboard so it does not tip into the spinning bit.
Can I cut circles in thick hardwood with a trim router?
A compact trim router can do it, but slowly: use a 1/4-inch bit, 1/8-inch passes, and let the tool rest between passes so the motor does not overheat. For stock over 1 inch thick, a full-size router is the better tool.
Bottom Line
Cutting a circle with a router comes down to three things: a simple trammel jig you can build from scrap in twenty minutes, the radius measured to the cutting edge of the bit rather than its center, and shallow passes in the right direction. Get those three right and the router does the rest — clean, exact circles in any size, in any material, as many times as you need them. Build the jig once, keep it hanging on the shop wall, and you will reach for it every time a project calls for a round top, a speaker hole, or a ring.
Routers spin at very high speeds and can cause serious injury. Always follow your tool manufacturer’s safety instructions, wear appropriate protective equipment, and practice on scrap material before cutting your project piece.
