Figuring out how to route a circle with a jig is one of those skills that suddenly makes tabletops, lazy Susans, and speaker blanks feel possible. A circle jig locks the router on a fixed radius so the bit swings a true arc instead of a nervous freehand oval. With a solid pivot, the right bit, and shallow passes, you can cut disks or cutouts that look machined rather than sketched.
Guides
How to Route a Circle with a Jig Without Wander
How to route a circle with a jig: set the radius, anchor the pivot, cut in light passes, and keep the bit from skating off the arc.
Circle jig basics in plain language
A circle jig is a arm or plate that attaches to your router base and rotates around a pin or screw at the center of the desired circle. The distance from pivot to bit center is the radius. Commercial jigs often have indexed holes; shop-made jigs can be a strip of plywood with a pivot hole and router mounting holes. Accuracy comes from a snug pivot and a router that cannot twist on the arm.
Gear that helps circles stay round
- Plunge router preferred for dropping into the cut; fixed-base can work with care on outside cuts
- Circle jig with clear radius markings or a shop-made arm you can measure
- Upcut or straight bit sized for the waste you are removing
- Center pivot hardware that does not oblong the hole after one revolution
- Sacrificial backer under thin stock to limit tearout on breakout
- Clamps or non-slip pad so the workpiece cannot spin with the jig
How to route a circle with a jig
01
Mark the center and decide inside vs outside cut
Find true center with diagonals or a center-finding rule. Decide whether the bit cuts on the waste outside the disk or excavates an opening inside a panel. That choice changes which side of the line the bit sits on when you set radius. Write the finished diameter on the scrap so you do not reverse the offset later.
02
Set the radius from pivot to bit center
Measure carefully: radius is to the cutting edge that defines the finished circumference, which means accounting for bit diameter. For a disk, finished radius equals distance from pivot to the inner cutting edge of the bit. For a hole, it is to the outer cutting edge. Double-check with a test swing above the work before cutting.
03
Anchor the pivot and secure the work
Drive the pivot into a waste area or into a plug in the center if the hole will be filled later. The workpiece must not rotate; clamp it down. If the jig rides on the face, keep that face clear of chips that could lift the arm. A wobbly pivot makes eggs, not circles.
04
Cut in shallow revolutions
Plunge a little, swing a full circle, then deepen. Deep single-pass cuts bog the bit and can deflect the arm. Keep feed steady—rushing one quadrant and creeping through another leaves flats. For thick stock, several revolutions at increasing depth beat hero cuts.
05
Support the waste as you finish through
On the last pass, the waste disk or ring can drop and catch the bit. Use a backer, leave tabs to saw later, or support the cutout from below. Kill the power before the bit grabs a loose piece. That last eighth of an inch is where many circles get ruined.
06
Clean the edge and verify roundness
A light final pass at full depth can clean fuzz if the bit is sharp. Check diameter in two directions with calipers or a tape across center. If one axis is long, the pivot shifted or the work moved. Learning how to route a circle with a jig includes trusting measurements over optimism.
Shop-made jig tips
A plywood arm screwed to a spare baseplate is enough for occasional disks. Drill the pivot hole square, not angled. Keep the arm stiff—thin hardboard flexes and grows the radius under load. Label common radii with a marker so you are not recalculating every tray blank.
Problems that oval the cut
- Pivot hole worn egg-shaped
- Workpiece spinning under the jig
- Router twisting in a loose mounting
- Arm flexing on deep cuts
- Inconsistent feed speed around the circle
FAQ
01
Can I route a circle with a fixed-base router?
Yes for many outside cuts if you can enter the waste safely and keep the base flat on the jig. A plunge router is easier for stopped depths and interior cutouts because you can drop the bit at the start of the arc. If you only own a fixed base, start the cut in waste and swing carefully. Never force a deep plunge by tipping a fixed base.
02
How do I calculate radius for a circle jig?
Measure from the pivot center to the bit center, then adjust for whether you want the finished edge inside or outside the bit’s cut. Bit diameter matters. A quick scrap test is smarter than trusting a single tape reading. Write the setting that produced the correct diameter on the jig for next time.
03
What bit should I use to cut circles?
A sharp straight or spiral upcut bit clears chips well in deep passes. Larger diameters remove waste faster but need more power and a stiffer jig. For fine furniture edges, a smaller bit with a light cleanup pass often looks cleaner. Dull bits burn and wander.
04
Why is my routed circle not round?
Something moved: pivot, workpiece, or router on the arm. Flex in a skinny jig arm also changes radius under load. Check that clamps held and the pivot hardware is snug. Cut shallower passes so the arm is not fighting a heavy chip load.
05
Should I cut clockwise or counterclockwise?
Follow conventional routing direction for control—typically moving so the bit’s rotation pushes the work against the pivot rather than yanking the router outward. Exact feel depends on whether you are cutting inside or outside. If the router wants to run away, stop and reverse your travel direction on a scrap test.
06
Can I cut a circle in a finished tabletop without a center hole?
You can use jigs that clamp to the edges or use a center disk that adheres temporarily, depending on the design. Many shop jigs need a small pivot hole that you plug later. Plan the center treatment before you commit to a visible top. Practice on scrap with the same thickness first.
07
How deep should each pass be?
Stay conservative—often 1/8 to 1/4 inch in hardwood, sometimes more in soft pine with a sharp bit and stout jig. If the router slows or the arm deflects, you went too deep. Multiple clean revolutions beat one smoking cut. Depth discipline is what keeps circles true.