The circle is, in my apprehensive opinion, the Queen of the geometric shapes. Don't get me wrong; I similar all those squares, rectangles, triangles, octagons, and whatnot; just the circumvolve is the coolest of the bunch: smooth and pretty and endlessly useful. However, trying to draw a perfect circle without a blueprint is a claiming, 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 eat with a bit of water ice cream. Nosotros're hither today to aid you with the steps you've forgotten since high school geometry grade (or maybe never learned because you lot were as well busy passing notes with Susan Ellery!). We'll show yous the parts of a circle, how wide to cut fabric to fit a circle, and how to depict a circle without a pattern. We've likewise included a handy conversion from decimals to inches, which is necessary when working with Pi.

The parts of a circle

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 center of the circumvolve to the outside border

Diameter: the distance across a circle through its center indicate

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 diameter, expressed every bit the decimal iii.14

How broad to cut cloth to fit a circle

If you lot know the diameter of your circle, yous tin can employ 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 will be inserted into the tube (we take a great stride-by-step tutorial on how to insert a circle into a tube).

The formula: 3.fourteen (π) 10 diameter = circumference

Case: You desire a finished 12″ diameter base (a 12″ diameter circle) in a duffle bag.

three.14 ten 12 inches = 37.68 inches

(This works with the metric system every bit well: 3.14 ten 30 cm = 94.2 cm)

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

The circle should beginning 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 bag might be 30″ in peak whereas a shorter bucket might be only 10″.

Converting a Decimal to a Usa Ruler Measurement

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

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

In our instance we have 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 can employ 38⅝" as the width of the fabric piece you are cutting for your tube.

How to Depict a Circumvolve

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

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

To depict a circumvolve you lot demand to know its radius. As y'all learned above in the first department, the radius is one half of the diameter. In our case, one half of 13″ is half-dozen½".

The full circle method

  1. Utilise a sheet of lightweight paper (graph or blueprint paper works well) that is at least 1″ larger all around than the circumvolve you want to draw.
  2. Cut a slice of cord almost 4″ – 5″ longer than your radius. We used a 10″ length of string.
  3. Tie 1 end of the cord 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 total sweep.
  5. Measure from where the bespeak of the pencil touches the paper backwards by the length of the radius (in this case half-dozen½").
  6. Pin directly through the string into the paper at that exact indicate.
  7. Keeping the cord taut, depict a perfect circle using your homemade compass.

The folded quarters method

  1. Once again, start with a square of lightweight paper at least ane″ larger than the circle y'all want to draw.
  2. Fold the paper into quarters. Make 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 top and right side.
  3. Place a encounter-through ruler at the verbal center of the bottom left corner of your folded foursquare. Swing the ruler from the top to the bottom of the square, like a pendulum or compass, measuring and marking a dot at the 6½" point in three to four spots. You are creating a semi-circle arc. Make sure the stop of the ruler at the corner point doesn't shift position.
  4. Cut forth the arc through all the layers and unfold the finished 13″ circle. You can now use this newspaper pattern to cut your cloth circle.

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

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