No Hole Circle Cutting Jig for the Bandsaw

This is a Circle Cutting Jig for my Bandsaw that doesn't require drilling a hole in your workpiece for it to pivot around while being cut. It is accurately adjustable to make circles with diameters between 250mm - 1150mm (10" - 45"). This is my first Instructable and I was only planning on recording an instructional video for it, so I've taken screenshots to put this together. It was also my entry into a Wood jig making challenge that finished yesterday, hence the reason #woodjigs21 is mentioned.

I hope it helps or inspires someone to make circles. Lots. Of. Circles!

You will need:

18mm (3/4") Plywood - 2 lengths 900mm (3') long by the width of your bandsaw table.

Length of T-Track & matching router bit to cut the appropriate channel

T-Bolt & Nut to match T-Track

Strip of Hardwood cut to the size of your bandsaw mitre track

Holesaw drills 61 & 63mm (approx 2 1/2") or similar. The difference should be approx the same size as the holesaw kerf

2-Part Epoxy Adhesive

WoodGlue/Nails/Wood Screws

Pencil / Fine tipped marker

Table Saw/Track Saw/ Circular Saw & Straight Edge

Router

Bandsaw

Drill Bits

Sandpaper/Sander

Optional: Microjig Matchfit clamp & matching router dovetail bit

The first step is to cut the base. The width of this will be equal to the length of your bandsaw table from front edge to rear edge. Length approx 900mm (3'). Then cut a thinner piece that is the same length as the first piece, but is the width of the first board minus 140mm (5.5"). Then cut this down the middle lengthwise. These will be the two top panels. In my video I used 17mm black formply, but this is not necessary.

Then cut a strip of hardwood down to fit snuggly in the mitre slot of your bandsaw. Glue & screw this piece perpendicular to the underside of the base so that the base will line up with the front, back and left edges of the bandsaw table and hang out over the right side. And optional step here is to add a dovetail groove or two to accept a Microjig Matchfit clamp to secure the jig to the table, but I only added this for added safety. The location will depend on your own bandsaw. See my video for a better understanding.

Once the mitre track runner is dry, slide the base of the jig onto the table and into the bandsaw blade. When the front of the table and the jig are aligned, switch off the bandsaw and add a scrap piece of wood to the front to prevent it from travelling too far into the blade. Secure with glue and small nails. When this is dry, it will assure that the blade always cuts in the same location.

This jig works by attaching a 'donut' of wood to your workpiece with double-sided tape. This donut sits perfectly over the adjustable 'puck' that sets the circle diameters on the jig. The puck is cut from scrap ply at approx 63mm. The wood for the donut is also cut from scrap and should be a millimetre or two smaller that the puck. If this is not a perfect fit, you may need to sand down the puck to fit. I attached a bolt through the puck, chucked it in a cordless drill and spun it lightly on a belt sander to get an accurate, even shrink in the diameter. Alternatively, you could get a piece of large dowel and use a matching spade or forstner drill bit to get the right size in the donut, using a cut piece of dowel as the puck.

These photos show how the donut is stuck to the workpiece, however the outer diameter of the donut can not be cut just yet.

Using a forstner bit slightly wider in diameter than the nut you'll be using on your t-bolt, recess a hole in the centre of the puck for the nut to sit in. Then using epoxy, glue the nut in place. I used the t-bolt to align & centre the nut, and used some machine oil on the thread to prevent the epoxy fixing the thread.

NOTE: If you're just looking at the pictures, this bit will probably confuse you. Originally I tried making this jig without the t-track by just routing a groove with a dovetail bit to slide the t-bolt in. This didn't work so I added the t-track, but I cut the donut out before I made that change. Also not that at some stage you'll need to cut the t-bolt so that it does not protrude above the puck when on the jig.

Make sure the centre of the t-track will be perfectly perpendicular to the front teeth of the bandsaw blade. You can clamp your top pieces here as a guide track for your router to get this very accurate. Once it's done, install the t-track with small countersunk screws and slide your puck into the track. Then place the piece for the donut over your puck, slide the jig ((& the donut) onto the blade and rotate the donut piece until it actually resembles a donut.

Now that the donut is complete, use it on the puck to line up where the top pieces need to be attached. It doesn't have to be exact, but just be sure there are a couple of millimetres (1/8") gap from the out side of the donut to the inside of both top pieces, all the way along the jig. Glue and/or screw these pieces down permanently.

You can also cut a piece from a scrap the fill the gap at the top of the jig between the left and right top sheets. I cut a piece at the same time as cutting the donut & then trimmed the edges to fit in the gap. This stops the puck from travelling too close to the blade and provides a zero clearance & added support to the underside of your workpiece.

After all of these steps have been completed, it's time to now push the whole jig onto the blade. This will make a new cut in the right top sheet, and into the middle piece. If everything has worked as planned. the front of the blade should line up with the centre of the t-track.

Lock the puck into position and after sticking the donut to the centre of a scrap piece of wood (I used 3mm mdf here) push it onto the bandsaw blade and rotate the scrap to cut a perfect circle. Measure the diameter of the cut circle and mark the puck position on the t-track with a sharp pencil. Record this size as well.

Repeat this a number of times until you have an idea o an accurate scale to use. For every centimetre or inch you move the puck away from the blade, the diameter of the cut circle will increase double as the puck marks the radius of the circle. Once you have made accurate markings test this by cutting more scrap and adjusting according to your results. Once you are satisfied with the accuracy, use a fine tipped permanent marker to redo your markings.

And your Circle Cutting Jig is now complete!!!