Introduction: Simple Band Saw Circle Cutting Jig
A circle cutting jig is something I have needed for many projects over the years. The problem is you need one but you're in the middle of another more exciting project. In the past I've used something that works but isn't easy to use or setup.
This quick project will make cutting circles of any size on the band saw quick and easy to setup for all future projects.
Step 1: Tools and Materials
Step 2: Create Base of Jig
Cut two equal squares of plywood (mine are 16 x 16 in.). I selected two squares that are larger than the table of my band saw and could be taken from a scrap piece of wood I had in the shop.
Glue and nail a piece of hardwood to act as the stop for your jig. This piece of wood will bump up against the front of the table on the band saw. Make sure the stop is short enough that it doesn't run into any hardware or other irregular shapes on the front of your table (my stop measures 10 x 1/2 x 3/4 in.).
Step 3: First Cut
Using a fence (or straight board to act as a fence), make the first cut into the bottom board with the stop in place. I left 4 in. to the left of the blade to act as support for cutoff material.
Step 4: Runner
Using the table saw, cut a runner just shallower than the track of your table. Take small cuts off until it's just the right size. If you cut it too small (like I did), you can save it by cutting some reliefs in each end then use small screws to expand the ends of the runner.
Place some washers under the runner to elevate it above the surface of the table. Apply two sided tape on the runner and slide the jig in place and press down. Remove the fence and slide the jig off the table and attach the runner with screws.
Attach the second square of plywood to the top of the base square with a lot of screws (I ended up adding more in a future step).
Step 5: Cut Slot
Using a square, transfer the max depth of cut to the left hand side of the jig. Measuring an inch to either side of the center mark will indicate where to cut the 45 degree tracks.
Remove the top square and cut both 45 degree angles on the table saw.
Step 6: Reattach Top
Reattach top and secure with more screws as needed.
Step 7: Cut Slide
Using another scrap piece of plywood (17 in. long), cut 45 degree angles until it fits. You can make multiple lengths of this slide for different groups of circle sizes.
For example, this slide can cut circles with diameters ranging in 2-18 in, and 33-50 in. (by flipping the slide around). I will need to make another slide in the future if I ever want to cut a circle with diameters in range from 18 and 33 in.
Step 8: Route Slots
Using a router, cut a 5/16 in. slot starting 1 in. from one end and ending 2 in. from the other. Cut a 3/4 in. slot 3/16 deep on the narrower top of the slide.
Drill a 1/4 in. through hole 1 in. from the end and chamfer the bottom of the hole so the flat head screw is flush against the bottom.
Using a 7/8 in. forstner bit, drill a recess for the t-nut. Tap the t-nut in place to mark the location of the four tines. Remove the t-nut and drill small reliefs at those 4 locations.
Tighten down the flat head screw to secure the t-nut in place.
Note: I did not take pictures of grinding down the tip of the flat head screw. This was done using a bench grinder.
Step 9: Secure Slide
Insert the slide back in the slot and mark the location to drill a clearance hole for the carriage bolt.
Step 10: Build Star Knob
Print off the attached star knob template at 143% to have the 2 1/2 in. star knob size that I used.
You can actually use this formula along with the attached template to calculate what percentage to print the template off at to get your desired size of star knob:
Apply the template using spray adhesive. Rough cut the shape on the band saw and smooth out shape using a strip sander and disc sander.
Drill a 1 in. recess to allow for the thickness of the t-nut. Drill a 3/8 in. clearance hole through the star knob.
Using the same technique as before, mark and drill relief holes for the 4 tines of the t-nut.
Secure the t-nut in place using small wood screws at an angle.
Gluing on a thin piece of walnut is optional but I think it ads a little something that no one will ever see.
Step 11: Apply Finish
Sand everything up to 200 grit and apply 2-3 coats of water based polyurethane to help protect the wood.
Step 12: Cut Circles
To cut a circle, set the point on the slide to the radius of the desired circle. Measure from the side of the band saw blade to the center of the point. Tighten star knob to hold slide in place. Mark the center of the circle on your wood and drill a small hole the size of the point of the center of the slide. Slide the wood on the point of the jig while the jig is not attached to the band saw. Turn on the saw and slide the jig into place. Slowly turn the wood to cut the circle. Once the circle is cut entirely, turn off the band saw and remove the circle and scrap from the jig and saw.
Participated in the