This is not one of those square-peg-in-a-round-hole situations. But, if the idea of sewing a two-dimensional item (a flat circle) into a three-dimensional item (a tube) sounds like something from another dimension altogether, read on. We’ve broken it down into a simple step-by-step process and even show you two different methods. 

Let’s chat first about what we are not going to learn here. We’re not going to get into the math equations needed to figure out how to appropriately size the opening of the tube to fit the circle. This involves ∏ (or pi, but not the yummy cherry kind) and multiplication. And, we are not going to learn how to cut a circle without a pattern. But, lucky for you – because you are a super smart Sew4Home follower, we have another tutorial about those very topics: Make and Measure a Circle Without a Pattern.

For this tutorial, we are assuming someone with a calculator and graph paper has already figured out all the dimensions for you and provided you with a pattern for your circle (wasn’t that nice of them?).

If you are familiar with garment sewing and have inserted a sleeve, you’ll notice the similarities to this technique.

We show you two methods below, one with gathers and one without. When you use each is dependent on your project. The gathered method is usually best when your overall project has some softness or fullness, such as a bolster pillow.

The flat method works well when the circle is the base of a project, such as a tall duffle bag.

Gather all your materials

With gathers

Marking the circle and the tube

1. Following the directions for your project/pattern, cut out the circle (our sample uses an 8″ circle).
   
2. Following the directions for your project/pattern, cut out the rectangle to form the tube (our sample used a 12″ high x 23″ wide rectangle).
3. Fold the rectangle in half, right sides together, so it is now 12″ x 11½”. Pin along the 12″ edge.
   
4. Stitch along the 12″ edge, using a ½” seam allowance.
5. Press open the seam allowance.
   
6. The key to this technique is to make accurate quarter-panel marks on both the tube and the circle. To create these marks on the circle, think of it like the face of a clock. You will make four marks at 12:00, 3:00, 6:00 and 9:00.
7. Fold the circle in half, right sides together, and press lightly to set a crease.
   
8. Place a pin at both outer edges of the fold.
   
9. Open up the circle, then fold in half in the opposite direction, right sides together, aligning the two pins from the first fold. You can also omit the pins and just work with the pressed crease line as your guide.
   
10. Press lightly to set an intersecting crease line. Then, place a pin at both outer edges of the new fold.
    
11. Open up the circle. You should now have a pin at four points of the circle, like a clock face: 12:00, 3:00, 6:00 and 9:00.
12. Using a fabric pen or pencil, make a mark at at each point, then remove the pins.
    
13. Once your pins are removed, you may want to go back and enlarge each of the marks so they extend all the way to raw edge of the circle. You want the marks to be easily visible.
    
14. Set aside the marked circle.
15. Next, you need a matching set of marks on the end of the tube into which the circle will be inserted.
16. With the tube wrong side out, flatten it in half so the seam forms the left edge. At the right edge, place a pin in the fold.
    
    NOTE: It also helps to lightly press the fold opposite the seam. The crease line you set (as you did above with circle) gives you an additional guideline to follow when matching the circle to the tube. 
17. Open up the tube and flatten it in the opposite direction, bringing together the pin and the seam.
    
18. With the pin and the seam aligned, place a pin at both outer edges of the new fold.
    
19. As above, place a mark at the location of each pin.
    

Inserting the circle into the tube

1. Find the marked circle.
2. Run a gathering stitch around the entire outer edge, staying within the standard ½” seam allowance. ⅜” is a good seam allowance.
   NOTE: If you are new to machine gathering, check out our full tutorial.
   
3. Gather up the circle just slightly, leaving the thread tails long so you can adjust the gathers as needed.
   
4. Find the marked tube.
5. Place the circle into the marked end of the tube, right sides together, matching up the 12:00, 3:00, 6:00 and 9:00 marks on both pieces. It’s a bit like setting a lid upside down into a box.
   
6. Pin at just the marked points first.
   
7. Adjust the gathers as needed to ease the outer perimeter of the circle against the round base of the tube.
8. Fill in with additional pins between these points until the circle is pinned in place all around.
   
9. Using a ½” seam allowance, stitch the circle in place. It’s best to flip up the tube so you can stitch with the circle facing up. This way, you can insure the gathering stays even.
   
10. Stitch slowly and concentrate on keeping the seam allowance even.
11. Press the seam allowance open and turn right side out.
    
12. If you are working with a particularly stiff fabric, you may want to clip the curves slightly to allow more give around the curve of the circle. Or, see the notes below about stay stitching.

Without gathers, and with an optional lip

1. The marking steps are the same as above. First pin and mark the quarter points on the circle.
   
2. Then pin and mark the quarter points on the tube.
   
3. Insert the circle into the end of the tube, right sides together. Match up the marks and pin all around. It will be a bit more of a challenge then when you had the gathers to take up any slack, but with plenty of pins, you should be fine. (This is assuming that the person doing your pattern/project got the dimensions precise!) Don’t be afraid to use plenty of pins.
   
4. Using a ½” seam allowance, stitch the circle into place. Go slowly to keep the seam allowance consistent, and as above, stitch with the circle facing up as it will be easier to slightly ease along the way if need be.
   
5. Press open the seam allowance, and clip the curves if you have a heavier fabric that could use a little more “give.”
   
6. Turn the tube to the right side. If this is the base of a project, such as shown on our Beach Duffle above, you can topstitch around the circle to form a lip. This adds a professional look and gives the base a bit more stability.
7. Pin the bottom circle to the side of the tube around the very bottom.
   
8. Topstitch (in matching or contrasting thread, depending on the look you want to achieve) around the base with a ¼” seam allowance.
   
9. You can go slightly smaller or wider with your seam allowance. It should be based on the size of project you are working with. A tiny lip will look out of proportion around a large circle; likewise, a very wide lip will look bad on a small tube. Your project/pattern should have guidelines, but ¼” is a good place to start. Cotton is forgiving, so you can always rip it out and go again.
10. You project/pattern should also tell you if interfacing is required prior to assembling the circle into the tube.
    

A quick note about stay stitching

Stay stitching is a single line of stitching that simply helps stabilize the fabric to prevent stretching or distortion. In this technique, it can also provide you with a seam line to follow later when stitching the circle in place. And, in the non-gathered method, it can provide a stopping line for clipping your curve.

Run the line of stay stitching along the long edge of your rectangle prior to sewing it into a tube (in our sample, we would stay stitch the 23″ side).

Stitch the side seam.

Clip the raw edges of the end of the tube into which you are inserting the circle (of course, you may be inserting a circle into both ends). Clip approximately every ½”, taking care to cut up to but not through the stay stitching.

Insert the circle into the base and pin in place. The clips will allow the fabric to flare out to match the curve of the circle.

Use the line of stay stitching as your guideline to stitch the circle into place.

For more about this optional part of the technique, take a look at our Compact Barrel Tote and our Safari Duffle Bag. We used stay stitching on both of these projects.