Taking pictures while I work on projects has helped me immensely to recall what I did and will hopefully assist anyone who tries to copy or improve on my ideas.
A hardware chain store was visited to buy o-rings which fit into the cylindrical jar. The I.D. of the jar was roughly one inch. Three sizes of o-rings were purchased.
10 @ 1" OD, 3/4" ID (1/8" thickness)
2 @ 1" OD, 7/8" ID (1/16" thickness)
1 @ 15/16" OD, 11/16" ID (1/8" thickness) - Not used
Supplies and o-rings in the jar
Two of the 1" x 3/4" rings were put in the bottom of the jar and fit snuggly. The 1" x 7/8" ring rested on top but did not fit snuggly. The thicker o-rings were too small on the I.D. to allow the cork to fit inside.
The cork resting on the o-rings
The jar was filled with water and the cork floated against the lid. The buoyancy inadvertently provided friction against the cork which would not spin like a compass.
Compass about to be filled with tap water
Cork floating against the jar lid
Rotating compass while it could not spin
Thin slices of cork were taken away using a kitchen knife which proved to make cleaner cuts than a band saw. The knife was a fine edge santoku-style knife with a thin blade. Cork was slowly removed until it was negatively buoyant.
Using a knife to cut the cork
Scrap slices of the cork
When the cork sank in the jar it would easily spin as compass is expected to spin.
Corked magnet acting as a compass
- Drill and install waterproof whisker
- Test + evaluate