The classic re-usable shopping bag is one of the easiest sewing projects around. A few french seams a folded handle and you are on your way. This particular version is sometimes called a Morse Bag. I've posted fabric cutting tips and links to the original instructions here. Admittedly the one in the picture above is a bit fancier than the typical bag but still quite easy to pull off.
The beauty of this style of bag is that the french seams used in construction mean that the bag is fully finished inside and does not have to be lined. A great savings on fabric and time.
The one problem with the Morse style bag is that the bottom is not squared off. It works quite well the way it is, but most shopping bags have a flat bottom. Boxing corners is simple. You turn the bag inside out, line up the side seam and bottom seam. Stitch across the triangle and cut off the excess fabric, which leaves raw edges inside your bag or you leave the corners on which leaves funky crud collecting flaps in the bottom. Either way, it is no longer fully finished and is begging for a lining.
I decided to modify the bag with boxed corners and see if I could do it without requiring a lining. It turns out it is pretty simple.
Once you've made your bag, turn it inside out and look at the bottom corner. In this picture, I'm holding the corner on the right side with the seams together. You can see that I have adjusted the seams so that they go in opposite directions. In quilting circles, we call this nested. It is particularly important in the construction of the boxed corner. Trying to stitch through all of those layers should the seams allowances be lined up would be almost impossible.
With the seams nested, turn the bag right side out and pull the corner to a flat point. The black arrow in the pictures is on the side seam. The bottom seam is nested perfectly below it. I've lined my ruler up on the seam. It looks slightly off-kilter but it truly does go along the seam and through the point of the bag. The ruler is placed so that the straight edges is 1.5 inches above the point.
I've moved the ruler slightly in the photo above so that you can see the line I have drawn. I used a pink washable chalk pencil so that my line shows up on both the light and dark portions of the fabric.
This is one of those occasions where I strongly suggest using a couple pins. Put them in perpendicular to the line you have drawn. Pull them out before you sew over them. Stitch a seam directly on the line you have drawn. Note the bag is positioned so that the WRONG sides are facing and the RIGHT sides are out. That is OK.
You will end up with a dog ear on the outside of the bag.
Cut it off!
I used pinking shears and left a scant 1/4 inch seam allowance. That is a quilting habit. For bag construction you can make it a deeper seam if you like. I prefer the smaller seam because it leaves less bulk in the bag.
Now you can turn your bag inside out. Put the RIGHT sides together with the WRONG side showing. Carefully poke out those corners.
Nest your seams again. Make sure you have a nice straight seam showing.
Sew a full 1/4 inch seam. To reinforce the stitching and to minimize loose threads, I start stitching in about 1/4 inch and backstitch to the edge. I then sew across the seam. When I get to the opposite side a stitch to the edge and backstitch in a quarter inch. Then I cut my threads. It just leaves the edges a bit tidier.
Feel free to cover a rectangle of plastic or better upcycled cardboard and tack it to the bottom to make a stable bottom. Or leave it as is for wad up and go convenience
The french seams give these bags plenty of stability and strength. Make them out of almost any upcycled fabric or remnant. Stretchy knits work but they will stretch so you might want to make the bag a wee bit smaller.