The circumvolve is, in my apprehensive opinion, the Queen of the geometric shapes. Don't become me wrong; I like all those squares, rectangles, triangles, octagons, and whatnot; simply the circle is the coolest of the bunch: smooth and pretty and endlessly useful. However, trying to draw a perfect circle without a pattern is a challenge, and figuring out the proper size of an opening into which a circle can exist inserted requires working with Pi (or π), which is not the delicious kind y'all can swallow with a bit of ice cream. We're here today to aid you with the steps you've forgotten since high school geometry course (or peradventure never learned considering you were too busy passing notes with Susan Ellery!). Nosotros'll evidence yous the parts of a circumvolve, how broad to cut fabric to fit a circle, and how to describe a circle without a design. 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 outset with remembering what all the parts of a circle are called and how Pi (π) fits into the mix.

Radius: the distance from the heart of the circle to the outside edge

Diameter: the distance across a circle through its middle point

Circumference: the distance effectually the outer edge of a circumvolve

π or Pi: the name given to the ratio of a circumvolve's circumference to its diameter, expressed as the decimal 3.fourteen

How wide to cut textile to fit a circle

If you know the diameter of your circle, you can use a standard formula to figure out the width of the textile cut needed to make a tube. That width is the circumference of the circle that volition be inserted into the tube (nosotros have a groovy footstep-past-step tutorial on how to insert a circle into a tube).

The formula: three.14 (π) ten diameter = circumference

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

three.xiv 10 12 inches = 37.68 inches

(This works with the metric system too: 3.14 x thirty cm = 94.2 cm)

An important footstep many people miss at this point is forgetting to add actress (to both pieces) for the seam allowance. If you use a standard ½" seam allowance, yous demand to add i″ 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 example, that ways:

The circumvolve should start as thirteen″ in diameter.

The fabric should be 38.68″ in width

The height of your cloth cut is variable and dependent on your project. For example, a tall duffle bag might be 30″ in tiptop whereas a shorter bucket might be only ten″.

Converting a Decimal to a Us Ruler Measurement

If you are using Pi, recall it always returns a decimal number. If you already bargain with the metric system, y'all stone –  no conversion necessary.

For those of united states of america in the globe of inches, you need to find a yardage conversion.

In our example nosotros accept 38.68 inches. Harumph! The tabular array beneath volition requite you lot a shut-plenty ruler match.

The decimal .68 is closest to .63 or ⅝". We can utilize 38⅝" every bit the width of the material slice y'all are cutting for your tube.

How to Describe a Circle

If you have a supply of large compasses, you're in luck, and can easily draw yourself all sizes of circles. Simply you can also easily make your ain compass to draw a circle.

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

To draw a circle you need to know its radius. Every bit you learned in a higher place in the showtime section, the radius is one half of the diameter. In our example, one half of 13″ is 6½".

The full circle method

  1. Use a sail of lightweight newspaper (graph or pattern paper works well) that is at least 1″ larger all around than the circle you want to draw.
  2. Cut a piece of string about four″ – 5″ longer than your radius. We used a 10″ length of string.
  3. Tie one end of the cord 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 brand a full sweep.
  5. Measure from where the bespeak of the pencil touches the newspaper backwards by the length of the radius (in this example six½").
  6. Pin directly through the string into the paper at that exact indicate.
  7. Keeping the string taut, depict a perfect circle using your homemade compass.

The folded quarters method

  1. Again, showtime with a square of lightweight paper at to the lowest degree 1″ larger than the circle you desire to draw.
  2. Fold the paper into quarters. Brand sure your original square is even and true! Position the paper with its folded edges forth the lesser and left side and the open edges along the top and correct side.
  3. Place a meet-through ruler at the verbal eye of the bottom left corner of your folded foursquare. Swing the ruler from the top to the lesser of the square, like a pendulum or compass, measuring and mark a dot at the 6½" bespeak in three to iv spots. Y'all are creating a semi-circle arc. Make certain the end of the ruler at the corner signal doesn't shift position.
  4. Cut along the arc through all the layers and unfold the finished 13″ circle. You can now employ this paper pattern to cut your fabric circumvolve.

With your spiffy new circle, y'all tin can now sew together the side seam in the primary cloth cut. Then pin the base to the resulting tube and sew the tube to the circumvolve using a ½" seam allowance. The issue is a 12″ diameter finished base.

As mentioned in a higher place, for more on this technique, come across our tutorial: How to Insert a Flat Circle Into a Tube.