My Bandsaw Circle Jig actually started out as an idea for a disk sander jig I saw in one of my woodworking magazines. They used a sliding arm with a screw adjuster to fine tune the diameter of the circle. I thought this was neat and it slowly evolved into the arm I made for my bandsaw jig.
I already had an arm with T-slot track in it from the bandsaw project, so I figured that would get used in both jigs. You could cut on the bandsaw, then fine tune on the disk sander. The construction method I used before applies well here too. 3D print a runner to go in the miter slot, start with a base of 1/4″ MDF, then attach 3/4″ MDF on top to guide the sliding arm. I CA glued the runner in place with it all aligned, and then screwed it in from underneath.
I don’t have any features to keep the adjustment arm locked down because the disk sander’s movement should push the work piece into the table and keep it stable. Hopefully that theory continues to work out for me.
The new thing here is the adjuster. The wood magazine had something with a T-nut and bolt. It was fine, but I figured a printer could do better. The knobs were something I had designed earlier. Each holds a 1/4″-20 coupling nut. The adjustment screw is a bit of threaded rod with a coupling nut bonded to one side. The other was rounded via a drill and bench grinder. The knob will glue on to the nut and the rounded end will push up against a hard stop. Having it rounded should mean there is only point contact and will make for smoother more even adjustment.
The adjuster uses a bolt in the t-track of the adjustment arm to clamp itself down in the rough position. I added a block to the bottom of the jig and bonded a big fender washer down for the head of the adjustment screw to contact. It should be a very firm stop and won’t wear easily.
Putting it all together, and with a few coats of polyurethane to keep the MDF stable, I tested it with another sharpening wheel. My last one was a little small, so I made a new bigger thicker one. The only thing to note is that doing heavy sanding in one spot will load up the paper badly. Sliding down the table occasionally will help even out the wear.
I have a router circle cutting jig from milescraft that works pretty well. It screws down a center and uses your router on an adjustable arm to make big circles. It does take a bit of setup though, and anything under about a foot in diameter is pretty awkward. There are loads of bandsaw jig ideas, so why not add mine to the pile? I think I have three things that are slightly unique in this design. Not revolutionary, but a bit different.
1. I started with a 3D printed miter slot runner. It is T shaped so once you slide it in the jig can’t come up off the table. Most folks make wood runners. Those are fine, but with printing it is a lot easier to dial in a T-slot so that the jig can’t lift. It comes with countersinks for #6 mounting screws.
2. The jig needs some kind of sliding arm to hold the piece being circle cut and set the circle radius. Dovetail slots and all sorts of things are employed. I took a T-track and glued it into a piece of 3/4″ MDF. Even 1/2″ screws would have been too long, so I just used epoxy. It holds well. A look from underneath shows that a bolt and knob let you lock down the circle radius arm in position.
3. To hold the work piece, most jigs use a small nail sticking up from the adjuster arm. You would drill a small hole in the part and pin it on the nail in the jig. Instead, I wanted a more flexible solution. I cut a 1-1/4″ hold in the end of my adjustment arm so I could put in 3D printed holders. One is 1/2″ in diameter so I can cut a MDF circle for my buffer. The other has a countersunk hole so I can screw a small #6 screw into the work piece. Optionally, there is enough space there to double sticky tape the puck down and use the center hole for alignment. I can print all sorts of posts or pins to suit my cutting needs.
To put that all together, a piece of 1/4″ MDF was CA glued to the runner (temporary) and pushed into the saw till it reached the middle of the jig. I glued a little stop in front so it would hit the bandsaw bed and stop in the same place every time. I then glued on 3/4″ MDF around the centered adjustment arm. That gave me enough material to screw on, from underneath, the glued runner. That all got pushed in again to the saw to cut through the new 3/4″ MDF.
I did some measuring, marked our the rough radius locations, and coated everything in a few coats of thinned polyurethane. It struggles a bit with anything under a few inches in radius, but a different blade would help. Up to 2 foot circles are possible. Above that and I will go to the router jig. To try it out, I made a sharpening wheel for my buffer out of 3/4″ MDF.
Set the runner to the appropriate radius and lock the knob
Install the square of material to be cut on the peg