Bandsaw Circle Jig

It seems that we all need to cut perfect circles in the shop from time to time. Cutting circles can be done in several ways. The Instructable that follows is my method for cutting them at the bandsaw.

Provided you already have a bandsaw, this is a very inexpensive shop jig that can be used over and over and should last several years.

Each bandsaw is going to be a little bit different so, it's important that you take measurements directly from your bandsaw. Additionally, cutting circles on the bandsaw requires a fairly small blade to prevent binding of the blade. I typically run a 1/4" blade with a low tooth count on my bandsaw when cutting circles.

Special thanks to mtairymd for his usual awesome work on the plans!

Tools:

• Bandsaw
• Table saw
• Drill / Drill bits
• Forstner Bit - Appropriate for the Threaded Insert Head

Material:

• 3/4" Ply - Can substitute with other stable material
• Miter Slot Runner - Hard plastic, hardwood, or metal
• CA glue
• Wood glue
• Screws

Full plans and video tutorial provided.

I used 3/4" Baltic Birch plywood to build my jig. I chose 3/4" thick to accommodate the threaded insert that will be used in a later step.

For my 14" bandsaw, I chose to make my base 22" wide by 24" deep. You'll want 2 pieces cut to this dimension.

The first step is to establish the saw kerf in the base of the jig. Using the bandsaw's fence, cut the center kerf about 1/2 way through the jig base. Do not remove from the saw.

Note: To accomplish this at the bandsaw, it's important that your bandsaw is set up properly and tracks well using your bandsaw's fence. Setting up your bandsaw is not part of this instructable. However, I would suggest viewing videos from Alex Snodgrass for excellent tutorials for setting up your bandsaw.

The next step is to install the runner. This runner should fit snugly in your bandsaw's miter slot. The fit of the runner is important! It needs to be narrow enough to slide smoothly in the slot but, wide enough so that there's no side to side play. The runner also needs to be slightly thinner than the depth of your miter slot.

Note: Although I used hard plastic for my runner, hardwood, or steel runners would work as well.

Predrill the runner with some mounting holes and countersink them to accept your screws.

Set some pennies (or similarly sized objects) in the bottom of the miter slot to raise the runner slightly above the surface. Apply CA glue (super glue) to the runner and set the base down on the runner. Apply weight to the base until the CA glue is cured.

Note: Applying a quickset activator to the bottom of the base will speed up the curing of the CA glue.

Once the CA glue is cured, remove the base and runner from the saw and secure the runner with screws.

Next up, we need to install the backstop for the jig. On my saw, this stop will stop against my fence rail and allow me to clamp this block directly to this rail. If your saw has a different fence setup, you may need to devise a stop and securing option that better fits your saw.

I cut a 3/4" by 3" strip of Baltic Birch plywood for the stop. I also cut a small notch to fit over the runner from the previous step as this stop will be attached directly to the base.

Note: After using this jig for a while, I notice that there is just a little bit of flex in this stop. To avoid this flex, simply laminate 2 of these strips together before attaching them to the bottom of the base.

To attach the stop, clamp the stop under the base and attach with glue and screws.

Next, put the base back on the saw and continue the saw kerf until the stop reaches the fence.

Using a square, locate the front of the blade and draw a line to the outside edge on the base. It's important that the pin is located at the leading edge of the blade.

There are 4 pieces to the cutting deck that will be covered in the next couple of couple of steps.

The first step is the support deck to the left of the saw blade. The only purpose of this portion is to support the workpiece as you're cutting your circles.

Using the second piece from the earlier step, cut this piece to fit the measurement from the left edge of the jig to the left edge of the saw kerf. This piece should fit flush on the left edge, front, and back without interfering with the saw kerf.

Apply this piece to the left side of the base using glue.

Note: I used a couple pin nails to secure it until the glue dried to speed up the process.

The next step is to build the sliding block out of the remaining piece of plywood leftover from the previous step.

Using the line drawn at the front of the blade in a previous step, I measured out approximately 1 1/2" from each side to determine the final dimension and location of the slider piece. Transfer these marks to the remaining piece of plywood to be cut at the table saw.

Set the table saw blade to 45 degrees and cut the center.

Note: Keep all the pieces! These are the final pieces to finish the jig deck.

Set the 3 pieces created in the last step on the base, use some ship material to create a little space around the actual slide block before securing the front and back of the deck.

Note: I used some card stock to create enough space for the slide block to slide easily in the groove.

Secure the front and the back pieces of the deck using glue. I used pin nails to secure these pieces until the glue dried.

Note: Don't get glue too close to the edges where the slide block will be. Any squeeze-out in this area could interfere with the function of the slide block.

Note: After using this jig for a while, I noticed that the glue alone wasn't enough to secure these pieces. I added screws to the front and back sections of the right side to better secure them.

Locking the block in place requires a threaded insert in the bottom layer of the base.

I started with a forstner bit to recess the head of the insert below the surface of the bottom layer. Then, using the appropriate sized bit drilled all the way through the bottom layer and installed the threaded insert.

Note: I used an F-style clamp to set the insert into the hole and flush with the surface.

I used a 1/4" 20TPI threaded insert and bolt/knob for this jig.

If you've made it this far, you've noticed that I have had some learning moments with this jig being in use for a while. This step will be no different!

Staying on the line drawn earlier (at the front of the bandsaw blade) drill a small hole to set the pin.

Note: I used a cut off finish nail for my pin. Use an appropriate sized drill bit for the pin you use in your jig.

Lessons Learned: When I originally built this jig, my assumption was that the sliding block would handle pretty much any sized circle I wanted to cut. It didn't take long before I needed to cut a larger circle than the jig was designed for. I realized that I could flip the block around so that the pin was to the outside of the jig which greatly increased the capacity of the jig. Additionally, an even longer slide in block could be easily made to further increase the capacity of this jig.

One other thing I would do to improve the functionality of this jig would be to install a stick down tape measure in a groove on the sliding block. This would make it much easier to determine the size of the circle to be cut. There's a new bandsaw in my future which will dictate this jig being rebuilt. These additional features will be added and provided in a future video.

As you can see, this is a fairly simple and quick shop jig to make. The jig has made an appearance in several of my videos and has really increased my circle cutting abilities in my shop!

I've certainly made some wonderful projects using this jig!

I hope you've enjoyed this Instructable as well as the free plans and video!