When I wanted to draw a big circle for a project I always resorted in the tie-a-pencil-with-a-string method. With this method, although straightforward, I never managed to make a perfect circle as my hand which held the pencil always moved in and out of the path, thus producing a wobbly circle. Fed up with imperfection, I decided to make a beam compass, which compared to the string is more stable.
A beam compass is a compass with a beam and sliding sockets or cursors for drawing and dividing circles larger than those made by a regular compass.
My design utilizes a threaded rod and is capable of drawing circles of nearly 2 meters in diameter! This design can be easily scaled up, by adding more threaded rods as extensions and coupling them using jam nuts, but this is out of the scope of this instructable.
One disadvantage of this device is that in order to set the needle and the compass at the desired place, one has to manually turn the nuts. And this takes some time...
Step 1: Materials
For this construction you will need :
- a metallic threaded rod M10 (1 meter long)
- 4 washers
- 5 nuts (4 x M10 and 1 x M14)
- a wood screw
- two component epoxy glue
- a pencil
Prefer a hexagon shaped pencil or a carpenters elliptical shaped one as I have used.
A circular pencil won't hold easily in place.
Step 2: Make the Needle
Take the M14 nut and glue the wood screw on its surface.
Look the above photo.
I used two component epoxy glue, as it makes very strong bonds.
Allow the glue to set properly and don't rush.
The manufacturer of the glue I used mentions that the glue attains its maximum strength and hardness progressively in 4 days.
Step 3: Assembly
After the needle has been made you are practically done.
Look at the photos to understand the assembly procedure.
Step 4: Scribe a Circle (or Two!) and Measure Π
These two concentric circles were constructed for the sake of my other instructable called:
I wanted to approximate the value of the mathematical constant π, so to get more precise results I needed 2 big circles.
With this beam compass it was easy as pie (pun intended!).
The outer circle has a diameter of 60 cm and the inner of 56 cm.