The circle is, in my humble opinion, the Queen of the geometric shapes. Don't go 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. However, trying to draw a perfect circle without a design is a claiming, and figuring out the proper size of an opening into which a circle tin be inserted requires working with Pi (or π), which is non the delicious kind you tin eat with a chip of ice foam. We're here today to help you with the steps you've forgotten since high schoolhouse geometry class (or maybe never learned considering you were too decorated passing notes with Susan Ellery!). We'll show you the parts of a circumvolve, how wide to cut fabric to fit a circle, and how to describe a circumvolve without a pattern. Nosotros've also included a handy conversion from decimals to inches, which is necessary when working with Pi.

The parts of a circumvolve

Permit'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 centre of the circle to the outside edge

Diameter: the distance across a circle through its center betoken

Circumference: the distance effectually the outer edge of a circle

π or Pi: the proper noun given to the ratio of a circle'due south circumference to its diameter, expressed as the decimal 3.14

How broad to cut fabric to fit a circumvolve

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

The formula: 3.14 (π) x diameter = circumference

Example: You desire a finished 12″ bore 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: 3.14 x 30 cm = 94.2 cm)

An important step many people miss at this point is forgetting to add extra (to both pieces) for the seam allowance. If you utilize a standard ½" seam allowance, you need to add 1″ to the bore of your circle ( the diameter increases by double the seam assart)and 1″ to the width of your fabric (½" for both sides of the seam allowance). In our example, that means:

The circle should start as 13″ in diameter.

The fabric should be 38.68″ in width

The height of your fabric cut is variable and dependent on your project. For example, a tall duffle pocketbook might be 30″ in top whereas a shorter bucket might exist just 10″.

Converting a Decimal to a US Ruler Measurement

If y'all are using Pi, recall it e'er returns a decimal number. If y'all already deal with the metric system, you rock –  no conversion necessary.

For those of us in the earth of inches, you demand to find a yardage conversion.

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

The decimal .68 is closest to .63 or ⅝". We tin use 38⅝" as the width of the fabric piece you are cutting for your tube.

How to Draw a Circle

If you have a supply of big compasses, y'all're in luck, and tin easily draw yourself all sizes of circles. Just you tin also easily make your ain compass to depict a circle.

To starting time, y'all need to know how big you want your circumvolve (the bore). For our ongoing example, we want a xiii″ diameter circle

To draw a circle you need to know its radius. Every bit you learned in a higher place in the first section, the radius is one one-half of the diameter. In our example, one one-half of thirteen″ is vi½".

The full circle method

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

The folded quarters method

  1. Again, start with a square of lightweight newspaper at least 1″ larger than the circle y'all desire to draw.
  2. Fold the paper into quarters. Brand sure your original square is fifty-fifty and true! Position the paper with its folded edges forth the lesser and left side and the open edges along the top and right side.
  3. Identify a see-through ruler at the exact center of the bottom left corner of your folded square. Swing the ruler from the acme to the bottom of the square, like a pendulum or compass, measuring and marking a dot at the 6½" point in three to iv spots. You are creating a semi-circle arc. Make certain the end of the ruler at the corner indicate doesn't shift position.
  4. Cut along the arc through all the layers and unfold the finished 13″ circle. You can now utilize this paper pattern to cutting your cloth circle.

With your spiffy new circumvolve, you lot can now stitch the side seam in the principal textile cutting. Then pin the base to the resulting tube and sew together the tube to the circle using a ½" seam assart. The result is a 12″ diameter finished base of operations.

Equally mentioned higher up, for more on this technique, meet our tutorial: How to Insert a Flat Circumvolve Into a Tube.