Circle-Cutting Jig

Round out your shop with this bandsaw sled

When it comes to making circular discs, I find routers outfitted with trammels to be loud and messy. I prefer to use my bandsaw, which I have outfitted with this very versatile jig. Basically a plywood sled that registers in my saw’s table slot, the jig makes for fast, safe, reliable work. In use, the workpiece rotates on a pivot pin that projects from a sliding bar, allowing lateral adjustment for circles of varying diameters. On my Laguna model 14-12 saw, I can cut disks from 3" to 30" in diameter. I use a 1/4" blade for most cuts on this jig. Capacity may vary, depending on the size of your saw’s table. 

The jig isn’t hard to build, and it will be an afternoon’s work well spent toward expanding your woodworking capabilities. I’ve used it to make cutting boards, tabletops, and circular steam-bending forms. A recent large telescope project required 23"-diameter disks for its rotating base. In another project, I made round ice-skate drying racks for a local club’s fundraiser. With this sled in your shop, you’ll have the excuse to explore the world beyond rectangles.

Order of Work

  • Size sled to fit your saw.
  • Rout slot and drill holes.
  • Make pivot bar and mount miter bar.
  • Make and mount travel stop.
  • Prep for use.

Simple construction, big benefit

This jig consists of a 3/4" plywood sled, the Kreg Jig and Fixture Bar (cut in two), and a handful of additional hardware (See Buyer’s Guide, p. 69). Part of the bar screws to the underside of the sled to serve as its runner, the other part serves as the pivot bar. The pivot bar houses a 1/8"-dia. pin that projects into a hole on the underside of a workpiece to act as a pivot point. Connector bolts with thumbscrews lock the pivot bar to locate the pivot pin at the desired distance from the blade. The star knob and bolt in the L-shaped anti-tilt/stop block allows fore-and-aft fine-tuning of the sled location to ensure precise positioning of the pivot pin in relation to the blade teeth. 

1. Determine length. Measure from fence rail to outfeed end of bandsaw table, then add 13⁄4" (overhang on rail). 
2. Determine width. Measure from the table’s outside edge toward inside edge (right to left), leaving room for a parked fence. Then add about 6" to accommodate cutting larger circles.
3. Find pivot slot centerline. Measure from outfeed end of table to teeth of blade.
4. Find pivot bar slot length. Measure from the right edge of your planned sled to 1⁄2" from the blade.

Rout the slot, drill the holes, and mount the hardware

Rout the slot as shown. Then drill counterbores for the pivot bar lock 3-3/8" from the edge as per the drawing on page 53. Slide the bar in the slot to ensure that its top sits above the counterbores’ depth. Drill 1/4" holes through the counterbore centers. Round the sled corners, then ease the edges with sandpaper.

Next, cut a 12" length from the aluminum bar, and drill two 1/8" holes for the pivot pins, locating them 1/2" and 5-1/2" from one end. (You’ll use the endmost pivot point for small discs, and the other for larger discs.) Now, drill and tap holes into the bar’s edges. Then adjust the plastic screws in the offcut section of the bar so that the bar slides in your bandsaw’s table slot freely but without slop. Measure for the stop block as shown. From 3/4 × 3-1/2" stock, crosscut one piece to your stop block measurement plus 1/16". Also cut a 4"-long piece for the anti-tilt block. Install the threaded insert in the stop block at the center of your fence rail, and mount the stop assembly. To finish up, sand the top surface smooth, then shellac and wax it to minimize friction. Then insert the 3" bolt through the star knob and stop block.

Rout the slot. Attach a fence parallel to the pivot slot layout, and on the left side of the router. Position a stop so the slot ends about 1⁄2" from the blade’s path and rout the slot in several light passes, pushing the router forward.

Tap the bar. Cross-drill through the bar with a #29 bit at the two pivot pin locations, then use a #8-32 tap to cut threads. Install brass-tipped setscrews to anchor the pivot pins.

Mount the bar. Place the sled on your saw’s table to mark the table slot location. At the bench, mount the bar squarely and flush with the outfeed edge.

Measure for the stop. For round fence rails, set your combination square to an even measurement and rest it on the table. Then use a smaller square to gauge the distance between the top of the table and the lower edge of the fence rail.
Mount the stop. Set the stop assembly on the sled bottom about 1⁄8" in from the infeed end, and mark and drill the pilot holes. Counterbore the anti-tilt block so that the screws reach 5⁄8" into the sled. 

Set up the sled, then cut a circle

To prepare the sled for its first use, make the initial cut and set the stop. To setup for a cut, place the sled against the stop, set the pivot point away from the blade the distance equal to your desired radius. (For very large-diameter work, reverse the bar to locate the pivot points outboard.) Drill a 1/8"-diameter hole, 3/8" deep in the center of the underside of your disk blank. With the sled pulled away from the blade, place the blank on the pivot pin. Turn on the saw and advance the sled until the stop contacts the fence rail. Then rotate the work in a complete circle.

Make initial cut, and set the stop. Mount and carefully advance the sled into the running sawblade. Stop when the teeth intersect the center of the slot. Hold the sled steady, turn off the saw, and adjust the stop screw to contact the rail. Then lock that position with the knob. The anti-tilt block should tuck snugly under the rail to prevent the sled from tipping with large work.

Cut a circle. Adjust the pivot point to your desired radius from the blade and mount the blank. Push the sled forward until the stop screw meets the fence. Then rotate the blank to complete the cut, using push blocks for a good grip on the top surface.

Looking Ahead

In the next issue, I’ll describe the spindle sander jig I devised to smooth the edges of bandsawn discs. See ya next issue!

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