In this step, you will prepare the fold-down top, iron the bag, sew down the fold-down top, and then trim it out.
At the ironing board, fold down the top edge 2 inches, and press, aligning the stitch line with the stitch line in the bag beneath. The triangular cutouts will allow the foldover to lay flat, with no bulk at the foldline. Align the flanges so that they lay next to each other, rather than overlapping.
Press all four top edges flat, then press out any other wrinkles in the bags.
If the foldover won’t lay flat because the fabric stretched when going through the sewing machine, align the flanges carefully, then steam out any extra fullness between them. Some fabric is more amenable to this than others, but you won’t know until after you start pressing. More steam is better. If the fabric refuses to behave, iron a tuck as needed to make it fit; this will not affect how the bag functions. You are most likely to see this issue in the gusset end that had to be trimmed off. The trim line will cover up most of the tuck.
Iron all the bags, folding over the top 2 inches, before proceeding to the next step.
At the sewing machine, set the needle to the center position. Start with a stitch length of .4mm to secure the stitch line. Place the foldover corner seam at the needle, aligning the seam margins underneath and stitch in the ditch from the top of the foldover to the raw edge, securing the foldover to the bag. Sew all four corners down before proceeding on to the next bag.
Sewing the corners down forces the bag to hold its shape and keeps the flange seams in place.
You may choose to swap these two steps: sewing the corners down in the ditch before pressing the foldover down. I’ve done it both ways. See what works for you.
At this point, if you ironed first and then sewed the corners, you may need to stop again and steam out any unwanted fullness in the foldover on the gusset. Remember, much of this fullness will be concealed beneath the trim line. A wider trim line will cover more sin so no one will ever know of this flaw but you.
Next, finish securing the foldover. Sew a line 3/8 inch from the folded top edge of the bag all the way around. This will keep the pressed edge in place. This is easiest to measure by keeping the needle in the center position and aligning the bag top edge with the side of the presser foot.
Sew all the bag edges before proceeding to the trim line.
Securing the Trim Line
The trim line encloses the raw edges and stiffens the opening of the bag. Your trim should be ½ to 2 inches wide as described in the unit on choosing trim.
Some notes on sewing on the trim. I do not measure trim in advance. I sew it down and cut it short as needed to minimize waste. I hide my trim joint under where the bag straps will go. That means I have to mark their location prior to adding the trim line. I don’t pin down the trim line, sewing it down by eye. The trim line needs to have its bottom edge just below the raw edge of the foldover. The narrowest trim, ½-inch wide, will just cover the raw edge. There won’t be much margin of error. I normally choose wider trim so that the bottom edge is just below the raw edge and the upper edge of the trim falls where it falls. Very wide trim (2 inches) is placed so that the bottom edge lays further down the bag and less of the foldover is covered up. I do match my top thread to blend in with the trim, just as I match my bobbin thread to the bag fabric.
First, decide which side of the bag is the front panel. You will mark where the left side bag strap will go, the only marking at this time. This will ensure that the join in the trim will be concealed.Lay the bag flat, front panel side up. Slide in your cardboard insert, the one that allows you to pin straps down without pinning both panels together. Lay your cardboard bag strap spacer on the left side of the panel, aligning it with the inner stitch line rather than the far edge of the sewn down flange. Make a tick mark across the raw edge of the foldover; this mark indicates the far side of the bag strap.
Mark all the bags in turn, one mark for the front panel of each bag. There is no need to mark the remaining strap locations.
At the sewing machine, place the trim ½-inch away from the tick mark, ensuring the trim join lays beneath the future bag strap. Arrange the trim so the bottom edge completely covers the raw edge and the top overlaps the foldover by a comfortable margin. The arrangement depends on the width of the trim and what you think looks best.
Sew down the trim, starting at the top edge, securing the trim with a .4mm stitch. Adjust the stitch to whatever length the trim wants. Allow the trim to unspool as you sew all around the bag. As you close in on your starting position, clip the trim to the exact length you need so the two ends butt together.
When you reach your starting point, cross back onto the original stitch line, pivot, and proceed sewing down the raw trim edge (the right side) to the bottom edge. Pivot and sew around the bag in the same direction. If any fullness accrues in the trim, you can trim it or push the excess under the bag strap. When you reach the end, secure the stitch with a few .4mm stitches.
The trim is sewed down with one continuous motion, all the way around twice, rather than starting and stopping a stitch line. It’s faster, when you have dozens of bags to sew.
Sew the trim line on all the bags before proceeding to the next step.
(This post is a draft from the upcoming book “Sewing Cloth Grocery Bags.” A complete list of the posts can be found here.)