The circle is, in my humble opinion, the Queen of the geometric shapes. Don't get me wrong; I like all those squares, rectangles, triangles, octagons, and whatnot; but the circumvolve is the coolest of the bunch: smooth and pretty and endlessly useful. Still, trying to draw a perfect circle without a pattern is a challenge, and figuring out the proper size of an opening into which a circumvolve tin can exist inserted requires working with Pi (or π), which is not the succulent kind you tin can swallow with a bit of ice cream. We're hither today to aid you with the steps you've forgotten since loftier schoolhouse geometry class (or maybe never learned considering you were also busy passing notes with Susan Ellery!). We'll show yous the parts of a circle, how wide to cutting fabric to fit a circle, and how to depict a circle without a pattern. We've also included a handy conversion from decimals to inches, which is necessary when working with Pi.

The parts of a circle

Let's start with remembering what all the parts of a circle are called and how Pi (π) fits into the mix.

Radius: the distance from the center of the circle to the outside border

Diameter: the distance beyond a circle through its centre signal

Circumference: the distance effectually the outer edge of a circle

π or Pi: the name given to the ratio of a circle's circumference to its diameter, expressed as the decimal three.14

How broad to cutting fabric to fit a circle

If y'all know the diameter of your circle, you lot can apply a standard formula to figure out the width of the fabric cut needed to make a tube. That width is the circumference of the circle that will be inserted into the tube (we take a great step-by-step tutorial on how to insert a circle into a tube).

The formula: 3.xiv (π) 10 bore = circumference

Example: You want a finished 12″ diameter base of operations (a 12″ bore circle) in a duffle bag.

3.fourteen x 12 inches = 37.68 inches

(This works with the metric system equally well: 3.xiv ten thirty cm = 94.2 cm)

An of import footstep many people miss at this signal is forgetting to add extra (to both pieces) for the seam assart. If you lot use a standard ½" seam allowance, yous need to add together 1″ to the diameter of your circle ( the diameter increases by double the seam allowance)and 1″ to the width of your fabric (½" for both sides of the seam allowance). In our instance, that means:

The circle should showtime as thirteen″ in diameter.

The fabric should be 38.68″ in width

The height of your textile cut is variable and dependent on your project. For instance, a tall duffle bag might be 30″ in superlative whereas a shorter bucket might be only 10″.

Converting a Decimal to a U.s. Ruler Measurement

If you are using Pi, remember it always returns a decimal number. If y'all already deal with the metric organization, you rock –  no conversion necessary.

For those of us in the world of inches, you need to find a yardage conversion.

In our example we have 38.68 inches. Harumph! The table below will give y'all a close-enough ruler match.

The decimal .68 is closest to .63 or ⅝". Nosotros can use 38⅝" as the width of the fabric slice you are cut for your tube.

How to Describe a Circumvolve

If y'all accept a supply of large compasses, you're in luck, and tin can easily draw yourself all sizes of circles. Only yous tin can also easily make your own compass to draw a circle.

To get-go, y'all need to know how big you desire your circle (the diameter). For our ongoing example, we want a xiii″ diameter circle

To draw a circle you lot need to know its radius. Equally you lot learned above in the kickoff section, the radius is one half of the bore. In our example, 1 one-half of 13″ is six½".

The total circle method

  1. Apply a sheet of lightweight paper (graph or blueprint paper works well) that is at least i″ larger all around than the circle you desire to describe.
  2. Cut a piece of cord almost iv″ – five″ longer than your radius. We used a 10″ length of cord.
  3. Tie one end of the string to a short pencil.
  4. Place the point of the pencil toward the outer border of the newspaper with enough room from the edge to brand a full sweep.
  5. Measure from where the point of the pencil touches the paper backwards past the length of the radius (in this case 6½").
  6. Pin directly through the cord into the paper at that exact signal.
  7. Keeping the string taut, draw a perfect circle using your homemade compass.

The folded quarters method

  1. Again, start with a foursquare of lightweight newspaper at least one″ larger than the circle you lot want to draw.
  2. Fold the paper into quarters. Brand sure your original square is even and true! Position the paper with its folded edges along the bottom and left side and the open edges along the height and right side.
  3. Identify a come across-through ruler at the exact heart of the bottom left corner of your folded square. Swing the ruler from the top to the lesser of the square, like a pendulum or compass, measuring and marker a dot at the 6½" signal in three to four spots. You are creating a semi-circumvolve arc. Make sure the cease of the ruler at the corner betoken doesn't shift position.
  4. Cut along the arc through all the layers and unfold the finished 13″ circle. You tin can now use this paper pattern to cutting your textile circumvolve.

With your spiffy new circle, you can now stitch the side seam in the main textile cut. And so pin the base of operations to the resulting tube and sew the tube to the circumvolve using a ½" seam allowance. The effect is a 12″ bore finished base.

Equally mentioned above, for more than on this technique, run across our tutorial: How to Insert a Apartment Circle Into a Tube.