Circular Slide Rule Instructions

Tools and materials:

• PostScript printer (600 dpi or better) with transparency stock
• Scissors
• A sharp hobby knife (or pocket knife)
• Thin cardboard (the back of an old writing tablet will do)
• White glue (and rubber cement if possible)
• A short piece of thin wooden dowel (1/8 in. diameter is ideal) or a bamboo skewer.
• Compass (optional)

Assembly instructions:

1. Make template. Download and print the two PostScript files. Part 2 (the slide rule cursor) must be printed on transparency. The two pages will look something like this:

   Part 1 (wheels)	Part 2 (cursor)

2. Assemble wheels. Cut out each of the four paper disks (two per side) and mount on thin cardboard. The finished wheels must have accurately centered holes for the axle (a piece of thin wooden dowel).

   Hint: To ensure accurate placement of the axle, Cut out a paper disk. Also cut out a piece of cardboard a bit larger than the disk. Punch a hole near the center of the cardboard with a sharpened piece of dowel. With the dowel still in place, trim excess cardboard from around the hole with a knife. Remove the dowel. Apply the paper disk to the cardboard with rubber cement. Before the rubber cement dries, hold the cardboard up to the light and center the crosshairs on the paper within the hole. After the cement dries, punch a hole through the paper. Cut away excess cardboard from the edge of the wheel.

   Cut along the blue lines.

3. Put the two large disks back to back, and insert the axle. Carefully orient the disks so that 1 lines up with 1 and 2 lines up with 5 (and 5 with 2). Glue the two disks together (Hint: if you cut a couple of glue holes in one of the disks beforehand, then a drop of glue in each hole will hold the disks together without disturbing their alignment).
4. After the glue has dried, add the smaller disks, one on each side. Cut out a cursor from the transparency sheet and fold it in half the short way, keeping the printed side inside so that the hairline will not rub off from handling. The cursor wraps around the stack of wheels so that the hairline can be used on all six scales. Punch holes for the axle at the two crosses, and fit the axle through all pieces. Note: depending on how wide you made the large disks, that the axle holes in the cursor may need to be more widely separated than the crosses indicate. Just make sure that both holes are centered precisely on the long hairline. When assembled, the cursor and the two small wheels should be snug on the axle but free to rotate.
5. Make two little cardboard washers to fit over the ends of the axle. Cut the axle so that it is just barely longer than the total thickness of the stack of disks and washers. Glue the washers in place. Use plenty of glue, but make sure that it doesn't get on any of the rotating parts. Set aside to dry thoroughly before using. Your finished slide rule should look something like this: