The circumvolve is, in my apprehensive opinion, the Queen of the geometric shapes. Don't get me wrong; I like all those squares, rectangles, triangles, octagons, and whatnot; but the circle is the coolest of the bunch: smooth and pretty and endlessly useful. However, trying to draw a perfect circumvolve without a pattern is a challenge, and figuring out the proper size of an opening into which a circle can be inserted requires working with Pi (or π), which is not the delicious kind you can swallow with a bit of ice foam. We're here today to assist you with the steps you've forgotten since high school geometry class (or possibly never learned considering you were as well busy passing notes with Susan Ellery!). We'll show you the parts of a circumvolve, how wide to cut fabric to fit a circumvolve, and how to depict a circle 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

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

Radius: the distance from the center of the circle to the exterior edge

Diameter: the distance across a circle through its centre point

Circumference: the distance around the outer edge of a circle

π or Pi: the name given to the ratio of a circle's circumference to its bore, expressed every bit the decimal 3.14

How wide to cut fabric to fit a circumvolve

If you know the bore of your circle, you can employ a standard formula to figure out the width of the fabric cutting needed to make a tube. That width is the circumference of the circle that will be inserted into the tube (we accept a great step-by-stride tutorial on how to insert a circle into a tube).

The formula: 3.14 (π) x diameter = circumference

Example: Yous desire a finished 12″ diameter base (a 12″ diameter circle) in a duffle bag.

3.14 ten 12 inches = 37.68 inches

(This works with the metric system too: 3.14 x 30 cm = 94.ii cm)

An important step many people miss at this point is forgetting to add together actress (to both pieces) for the seam allowance. If you use a standard ½" seam allowance, you need to add 1″ to the diameter of your circle ( the bore increases past 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 start as 13″ in bore.

The fabric should be 38.68″ in width

The height of your fabric cutting is variable and dependent on your project. For example, a tall duffle bag might be 30″ in pinnacle whereas a shorter bucket might be only 10″.

Converting a Decimal to a The states Ruler Measurement

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

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

In our example we take 38.68 inches. Harumph! The table below will give you a close-enough ruler match.

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

How to Draw a Circumvolve

If you have a supply of large compasses, you're in luck, and tin can easily draw yourself all sizes of circles. But you lot tin can likewise easily make your own compass to draw a circle.

To first, you need to know how big you want your circumvolve (the diameter). For our ongoing instance, we want a 13″ bore circumvolve

To depict a circle you demand to know its radius. As you lot learned higher up in the first section, the radius is 1 half of the diameter. In our example, one half of xiii″ is half dozen½".

The full circle method

  1. Utilize a sheet of lightweight paper (graph or design paper works well) that is at least one″ larger all around than the circle you want to draw.
  2. Cutting a piece of cord about 4″ – 5″ longer than your radius. Nosotros used a ten″ length of cord.
  3. Tie i cease of the string to a short pencil.
  4. Place the point of the pencil toward the outer edge of the paper with enough room from the edge to make a full sweep.
  5. Measure from where the point of the pencil touches the paper backwards by the length of the radius (in this case half dozen½").
  6. Pivot directly through the string into the paper at that exact point.
  7. Keeping the string taut, draw a perfect circumvolve using your bootleg compass.

The folded quarters method

  1. Again, start with a foursquare of lightweight paper at least 1″ larger than the circle yous desire to describe.
  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 up edges forth the top and right side.
  3. Place a see-through ruler at the exact center of the bottom left corner of your folded square. Swing the ruler from the top to the lesser of the foursquare, similar a pendulum or compass, measuring and marking a dot at the vi½" point in three to 4 spots. You are creating a semi-circle arc. Make sure the end of the ruler at the corner point doesn't shift position.
  4. Cut along the arc through all the layers and unfold the finished 13″ circle. You can now apply this paper pattern to cutting your material circle.

With your spiffy new circle, y'all can at present sew together the side seam in the principal fabric cutting. Then pin the base of operations to the resulting tube and run up the tube to the circle using a ½" seam assart. The event is a 12″ bore finished base.

Every bit mentioned in a higher place, for more on this technique, see our tutorial: How to Insert a Flat Circle Into a Tube.