I needed to make a quarter wheel section for the press drill I'm making, (instructable coming soon - being written as I go), with better accuracy than I could achieve through hand shaping with abrasive paper (my only real alternative). I don't own or have access to a lathe, but started thinking about how I could turn the piece of wood against a cutting tool in some other way.
I came up with the solution illustrated. It is more like planing a circle than wood turning. It's slow going, but I did end up with a far more circular piece than I could have achieved otherwise.
Step 1: Materials and Tools
* Tenon saw
* Coarse sandpaper
* Sanding block
* A vice
* Drill and bits
* Wood to make the disk out of
* Dowel or bar to use as a spindle
* Wood to make base board, 1" thick, wide and long enough to accomodate workpiece and chisel
* Wooden block to hold chisel
Step 2: Make the Base
First select a piece of wood to make a base. This needs to be wide and long enough to accomodate the circle you are making plus the chisel in it's retaining block of wood, and thick enough to secure the spindle. The piece I used in the photos is about 1/2" thick, and not really thick enough. I would use a piece at least an inch thick if I do this again.
Step 3: Rough Out and Mount the Circle
Mark out the workpiece. Rough it out with a saw, chisel, and coarse sandpaper. Try to get it as close to the desired circle as you can. It's a good idea to make lots of parallel cuts across the grain, going almost to the line, rather than trying to cut a series of tangents to the circle.
Drill the centre of the workpiece and a corresponding hole in the base to fit a spindle into. Fit the spindle through the workpiece and into the base. Ensure the piece is flush with the base and can turn comfortably. There should be no lateral play - otherwise you will end up with an oval, not a disk.
Step 4: Mount the Chisel
Position a chisel with its long edge flat against the base, so that it's blade is touching the work piece at a suitable angle for cutting. Get a fat block of wood and position it on top of the chisel so that the chisel is covered by as much wood as possible. Mark where the positions where the chisel passes the edges. Be careful not to cut yourself on the chisel whilst trying to hold it steady.
Cut a slot in the piece of wood which will hold the chisel in the position you marked. Don't cut any deeper than the width of the blade. Drill 2 screw holes in the piece of wood (the one screw shown in the photo isn't adequate).
Fit the chisel into the slot and screw the block down in position to cut. Only use one screw until you are happy with the final position. File the point off another screw and screw it directly above the chisel so it clamps it down (drill a hole first) (again, I did this after I took the photo).
Choose the angle of cut very carefully - working with a circular piece is deceptive!
Step 5: Start Cutting!
Rotate the workpiece so you find the highest spot. Turn the piece over if you need to so that you cut with the grain. Loosen the screw which clamps the chisel, and tap the chisel in with a mallet so that when you turn the piece it will cut a fine shaving. Tighten the screw, and turn the work piece so it cuts.
Repeat, repeat and repeat, turning the piece over as necessary to cut with the grain. Take extra care when cutting the end grain. If it gets really stuck, trim with across the piece with another chisel, or abrasive paper, until you can get going again.