At this point, you should have several grocery bags ready for the second pass. In this step, you will iron a crisp knife-edge on each of the six seams. Then you will sew a half-inch seam all the way around, front and back, producing a flange that will enclose all the raw edges. The flange will be sewn down in a later pass through the sewing machine, reinforcing the corners and helping to provide a skeletal structure for the bags.
Continue to use your walking foot. You will be changing stitch lengths to secure a seam line at its beginning and end and to reinforce the corners.
To be most efficient, I recommend ironing all the bags first and then sewing the flange on all the bags.Lay the bag down on the ironing board with a panel side down and the gusset exposed.
Pull the gusset to your left so that it lays flat on the panel, giving you a knife-edge on the right side, with the bag opening up and away from you.
Iron the right-side hem to a crisp knife-edge. Try to keep the seam line right at the outside edge of the flange you are making.
When you reach the corner, pivot the bag, again pulling the gusset away from the panel. Iron the bottom seam flange flat.
When you reach the next corner, pivot the bag again, and iron the left-side seam flat.
Flip over the bag and repeat the above steps, starting with the right-hand seam.
When you have finished ironing a bag, each of the six seams — right side, bottom, left side on the front panel and right side, bottom, left side on the back panel — should be pressed flat. Your bag should now have the shape of a paper grocery sack.
To keep those nice edges, lay each bag flat in a stack, with the gusset folded into the bag’s front and back panels.
When you have finished ironing the bags, go back to the sewing machine.
You will be sewing a ½-inch flange all around the six sides of each bag, using the presser foot as a measuring device. Set the needle to the left position. Lay the bag, front panel side down and gusset side up, with the right edge of the bag aligned with the presser foot.Start with a .4mm stitch to secure the seam line, then switch to a longer stitch length to accommodate your fabric. Sew down the right side seam, keeping that half-inch margin.
When you near the corner, pull the gusset fabric into a pleat, stacking the fabric as neatly as you can. Switch your stitch length to 1mm and sew to within a half-inch of the bottom.
How to Sew Over the Gusset
You will be sewing over the gusset fabric, pleating it up as smoothly as you can manage. Don’t catch more fabric in the pleat than you have to. The flatter the pleat, the neater the final seam will be.
When you are a half-inch from the knife-edge at the bottom of the bag (I measure this using my presser foot and by eye), lift the presser foot and pivot the bag. Sew another inch using the 1mm stitch to finish securing the corner.
Lengthen your stitch and sew the bottom flange.
When you are within an inch of the left corner, set your stitch length back to 1mm. Pleat the gusset fabric again, so you catch as little of it as you can manage and as before, sew up to a half-inch of the knife-edge.
Lift the presser foot and pivot the bag. Finish securing the corner with the shorter stitch.
Finish sewing the left side seam with your half-inch seam margin. When you near the end, shorten your stitch length back to .4mm to secure the line of stitching.
Flip the bag over, with the back panel side down, and repeat the process, sewing the right side seam flange, pivoting at the corner, the bottom seam flange, pivoting at the corner, and then the left side seam flange.
Reject Wrinkles with Careful Folding
As you finish each bag, lay them flat with the gusset folded within the front and back panels, to discourage wrinkles.When all the bags are finished, you will be ready for the third pass: snipping and then sewing the flange down.
(This post is a draft from the upcoming book “Sewing Cloth Grocery Bags.” A complete list of the posts can be found here.)