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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:

Approximate The Value Of π In Your Kitchen.

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.

<p>Nice work my friend,</p><p>Elegant solution to a common problem. I'll be making this. Thanks also to oggybear, for his contribution.</p><p>Many thanks for sharing.</p>
<p>Thanks for looking!</p>
<p>If you attach a piece of rod on the opposite side of the screw on the nut you would have a convenient handle to hold down the centre pin</p>
<p>That's a neat idea and I might as well do it. Thanks for sharing!</p>
<p>I mean't to say with a knob on it</p>
Braze the screw to the nut, much stronger
<p>Agreed. I would have welded it, if I weren't so lazy. But I had some leftover glue from another project and I gave it a go. Besides it's an alternative method of joining pieces of metal for people without a welder. Thanks for commenting!</p>
<p>Great work</p>
<p>Thank you!</p>

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