The circle is, in my humble opinion, the Queen of the geometric shapes. Don't get me incorrect; I similar 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 circumvolve without a pattern is a challenge, and figuring out the proper size of an opening into which a circumvolve can be inserted requires working with Pi (or π), which is not the delicious kind you tin consume with a bit of ice cream. We're here today to help you with the steps you lot've forgotten since high schoolhouse geometry class (or mayhap never learned because you lot were as well decorated passing notes with Susan Ellery!). We'll show you lot the parts of a circle, how broad to cutting fabric to fit a circumvolve, and how to draw a circle without a design. 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 circumvolve are called and how Pi (π) fits into the mix.

Radius: the distance from the center of the circumvolve to the outside edge

Bore: the distance across a circle through its center point

Circumference: the distance effectually the outer edge of a circle

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

How broad to cut material to fit a circle

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

The formula: iii.14 (π) x bore = circumference

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

iii.14 x 12 inches = 37.68 inches

(This works with the metric system as well: iii.14 10 xxx cm = 94.2 cm)

An important footstep many people miss at this point is forgetting to add together extra (to both pieces) for the seam allowance. If you use a standard ½" seam allowance, y'all demand to add 1″ to the diameter of your circle ( the bore 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 circle should outset every bit 13″ in diameter.

The textile should be 38.68″ in width

The top of your fabric cutting is variable and dependent on your project. For instance, a alpine duffle bag might be xxx″ in height whereas a shorter bucket might be simply 10″.

Converting a Decimal to a US Ruler Measurement

If you are using Pi, recollect information technology always returns a decimal number. If you already deal with the metric system, you stone –  no conversion necessary.

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

In our example nosotros have 38.68 inches. Harumph! The table below will give you a close-plenty 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 Draw a Circle

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

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

To describe a circle you lot need to know its radius. As you learned above in the starting time section, the radius is one half of the diameter. In our case, one half of 13″ is half dozen½".

The full circle method

  1. Use a sheet of lightweight paper (graph or design paper works well) that is at least 1″ larger all effectually than the circle you desire to draw.
  2. Cut a piece of string about iv″ – v″ longer than your radius. Nosotros used a 10″ length of cord.
  3. Necktie one end of the string to a short pencil.
  4. Identify the bespeak of the pencil toward the outer edge of the paper with enough room from the border to brand a full sweep.
  5. Measure from where the indicate of the pencil touches the newspaper backwards by the length of the radius (in this instance 6½").
  6. Pin straight through the string into the paper at that verbal point.
  7. Keeping the string taut, describe a perfect circle using your homemade compass.

The folded quarters method

  1. Again, start with a foursquare of lightweight newspaper at least 1″ larger than the circumvolve you want to draw.
  2. Fold the paper into quarters. Make sure your original square is even and truthful! Position the paper with its folded edges along the bottom and left side and the open edges forth the peak and right side.
  3. Place a encounter-through ruler at the verbal middle of the bottom left corner of your folded square. 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" signal in three to four spots. Yous are creating a semi-circle arc. Make sure the finish 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 at present use this paper pattern to cutting your textile circle.

With your spiffy new circle, you can now stitch 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 consequence is a 12″ diameter finished base.

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