The circumvolve 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; only the circle is the coolest of the agglomeration: smooth and pretty and endlessly useful. However, trying to draw a perfect circle without a blueprint is a challenge, and figuring out the proper size of an opening into which a circle tin be inserted requires working with Pi (or π), which is not the succulent kind you can consume with a bit of ice foam. We're here today to assistance you with the steps you've forgotten since high school geometry class (or maybe never learned because you were too decorated passing notes with Susan Ellery!). We'll testify you the parts of a circle, how wide to cut fabric to fit a circumvolve, and how to draw 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 circumvolve

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 center point

Circumference: the altitude around the outer edge of a circle

π or Pi: the name given to the ratio of a circle'south circumference to its diameter, expressed equally the decimal iii.14

How wide to cut fabric to fit a circle

If you know the diameter of your circle, you can apply a standard formula to figure out the width of the fabric cut needed to brand a tube. That width is the circumference of the circle that volition exist inserted into the tube (nosotros have a not bad step-by-footstep tutorial on how to insert a circle into a tube).

The formula: 3.14 (π) x bore = circumference

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

3.xiv x 12 inches = 37.68 inches

(This works with the metric system every bit well: iii.fourteen x 30 cm = 94.2 cm)

An of import step many people miss at this indicate is forgetting to add extra (to both pieces) for the seam allowance. If you use a standard ½" seam allowance, you need to add 1″ to the bore 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 example, that means:

The circumvolve should commencement as thirteen″ in diameter.

The material should be 38.68″ in width

The top of your fabric cut is variable and dependent on your projection. For example, a tall duffle bag might be thirty″ in tiptop whereas a shorter bucket might be just 10″.

Converting a Decimal to a U.s. Ruler Measurement

If you are using Pi, remember it always returns a decimal number. If you already bargain with the metric arrangement, you rock –  no conversion necessary.

For those of the states in the globe of inches, you lot need to detect a yardage conversion.

In our instance we have 38.68 inches. Harumph! The table beneath will give yous a close-enough ruler friction match.

The decimal .68 is closest to .63 or ⅝". We can use 38⅝" equally the width of the fabric piece y'all are cut for your tube.

How to Depict a Circle

If you have a supply of large compasses, yous're in luck, and can hands draw yourself all sizes of circles. But y'all can besides hands make your ain compass to draw a circumvolve.

To start, you need to know how large you lot want your circle (the bore). For our ongoing example, we desire a 13″ diameter circumvolve

To draw a circle you demand to know its radius. As y'all learned to a higher place in the first section, the radius is one half of the diameter. In our example, one half of 13″ is 6½".

The full circumvolve method

  1. Use a sheet of lightweight paper (graph or design paper works well) that is at least one″ larger all around than the circle yous want to depict.
  2. Cut a piece of string virtually iv″ – 5″ longer than your radius. We used a 10″ length of string.
  3. Tie one end of the string to a short pencil.
  4. Place the point of the pencil toward the outer edge of the paper with plenty room from the edge to make a full sweep.
  5. Measure from where the point of the pencil touches the newspaper backwards by the length of the radius (in this case six½").
  6. Pivot straight through the string into the paper at that exact point.
  7. Keeping the string taut, describe a perfect circle using your homemade compass.

The folded quarters method

  1. Once more, start with a square of lightweight paper at least 1″ larger than the circle you want to describe.
  2. Fold the paper into quarters. Make sure your original foursquare is even and true! Position the paper with its folded edges along the bottom and left side and the open edges forth the top and right side.
  3. Place a come across-through ruler at the exact center of the bottom left corner of your folded square. Swing the ruler from the summit to the bottom of the foursquare, like a pendulum or compass, measuring and mark a dot at the vi½" point in three to four 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 forth the arc through all the layers and unfold the finished thirteen″ circle. Y'all tin at present use this paper blueprint to cut your fabric circumvolve.

With your spiffy new circle, y'all tin can at present sew the side seam in the main cloth cut. Then pin the base to the resulting tube and sew the tube to the circle using a ½" seam assart. The result is a 12″ diameter finished base.

As mentioned above, for more than on this technique, see our tutorial: How to Insert a Flat Circle Into a Tube.