Bandsaw Jig for Glatt
 

In my lathe thread I mentioned these little covered boxes I make from discarded cardboard tubes. I cut a small plywood disk and glue it into the bottom, then turn a decorative lid for the top. To tart up the cardboard tube I glue birch bark or old book pages to the exterior and interior.

The birch covered boxes have topo maps inside or vice versa. The boxes with pages are pages inside and out.

To make multiple accurate disks, I used a jig.

Circle jig for the bandsaw

One of the craft fair items I’m making are small lidded boxes. This series is made from discarded heavy cardboard tubes that I’ve cut to length, lined with decorative paper and wrapped with either decorative paper or, in this sub-series, birch bark. I turned wooden lids on the lathe and cut ¼” plywood disks to glue into the bottom of the tube.

I can chuck the wood for the lids into the lathe as a square and then turn it round but to quickly make a lot of accurate disks for the bottoms calls for a circle jig for the band saw.
The simplest is just a piece of ¼” plywood with a small brad nailed up from the bottom of the ply at a distance from the edge equal to the radius of the desired circle, with the edge of the plywood immediately adjacent to the blade.

This is great for one-offs or occasional use, but for production runs with varying diameters I thought it would be nice to have something more robust and stalwart. Repeated use of the thin, relatively soft plywood quickly made the brad holes sloppy and it was fiddly at best getting the radius just right from below. I needed something adjustable, repeatable, accurate, and sturdy.

I figured putting the pin in a captive bar that could slide in a track would be a nice solution.

I kept the original jig as the base for the new design and figured the pin would need to be set in something solid that could still be adjustable. I wanted a pin that was stronger than the brad, by making the depth adjustable I could accommodate stock as thin as 1/8” as well as thick bowl blanks. I chose a hardened #6 x 1” wood screw from McFeely’s and set it into a sliding adjustable bar made from a piece of 1/2” x 1” Rock Maple, counter-sinking it from the bottom. I filed the screw tip so it leaves a finer, smaller hole in the disk stock. For really large material, like bowl blanks, I can swap the screw out with a longer #6 screw.

The radius of the circle is adjustable by sliding the wooden bar, for circles with larger radii the bar can be flipped end for end. The size range is 1” diameter to 26-7/8" (twice the throat depth of the saw)

I thought of a number of different methods for locking the bar; I wanted the lock to be positive as well as quick, without requiring a tool such as a screwdriver or wrench. I settled on using a cam lever. When I made the track I screwed a thin strip of rock maple to the edge of the plywood to act as the brake shoe between the bar and the cam lever. I didn’t wan’t the cam lever to act directly upon the sliding bar in case it might nudge to bar slightly out of position as the cam rotated into place. I waxed everything up that is supposed to move, and I glued the two pieces of ½” ply into place on the original jig-as-base on either side of the bar to create the track for the bar. The wax was insurance against glue seep.

I set a tension pin in place for the cam lever and finally glued a thin cover over everything. The final step was to rip a groove in the top of the jig for the pin to protrude through.


1. & 2. view of boxes

3. & 4. Orginal jig quickly heading towards swiss cheese territory

1. Bottom of jig showing miter slot guide.

2. The jig slides into position. I realize I need to clarify this step later.

3. Finished jig in position without guide pin installed yet.

1. Tension pin and cam ready to be installed

2. Cam locked against brake shoe - note gap

3. Cam open - no gap

4. w/o guide bar ready for cover to be glued

The top ready for glue.

I'm waiting for youtube to process a video I uploaded of the jig in action.

Wow. Thanks. I need to come back to this later when I have more than just a moment to glance at my phone

Recording this one handed, sawing is awkward with one hand

Sweeet.

B00M ... mind blown.
Very cool.

Kool.

OK, I'm looking at this more closely now and I don't understand what's happening. The cam lever presses against the shoe and locks the slide in a particular position.

The video isn't working for me, but is there a pin near the end of that slide that acts as a pivot point for the circles? By unlocking the cam lever, you slide the pivot point closer to or farther from the blade?

That's correct. The pivot pin is supposed to be perpendicular to the blade in line with the front of the teeth, although I find it works better when it is lined up with the gullet. Too far in or not far enough in causes the blade to pull out or push in, throwing the roundness off.

I'll take a few stills with close ups so you can see what is going on. Duginske talks about circle jigs in his book.

After using it for a while I've come up with a few ideas to make it even more handy, I made rule markings at 1/2" intervals and then brought them down and connected them to a perpendicular so I can easily take a square block and by setting the edges along the ruled lines the pin is automatically in the center of the block.