I first learned the machine blind hem stitch in my high school sewing class. It’s a really useful to stitch to know and very easy to do. The stitch simulates a hand done blind hem stitch by stitching a few straight stitches in the hem and then one zig zag to catch the body of the garment. I most often use it to hem pants or skirts. It's super fast to do and a great stitch to have in your arsenal of techniques.
It must be said that it’s not as invisible as a hand-sewn blind hem stitch but it’s faster and depending on the fabric and thread color it’s usually very hard to see. As always, if you’re unsure that you’ll like the finish, test it out on scrap of fabric. You can even try different colors of thread to see which is the most invisible. And remember even if you can see the stitch a little bit, it’s unlikely that anyone else will notice. The trickiest part of sewing this seam is prepping the fabric. It feels a little counterintuitive but after you’ve done it once or twice, it will make sense.
HOW TO SEW A MACHINE BLIND HEM STITCH
Step 1: Set up the machine for Blind Hem Stitch and attach blind hem presser foot if available. On my machine (a Brother CS6000i), it’s stitch number 09. It makes about 5 straight stitches and then does one zig zag to the left. (If your machine doesn’t have a special presser foot don’t worry about it. I learned without one.)
Step 2: Fold the hem of the fabric towards the wrong side two times and press. To hold it in place, insert pins with the point sticking out towards the bottom and the head in towards the top of the garment (the opposite of how you’d normally do it).
Step 3: Fold hem towards right side so that the heads of the pins are now on the right and there is a fold in the garment just to the left of the hem fold. Position the fabric under the presser foot with the garment fold touching the guard in the middle and the hem fold sticking out to the right. (If you don’t have a special foot just use the regular one and keep the fabric folded as you stitch.)
Step 4: Slowly start to stitch. The straight stitch should go into the hem fold and after about 4 stitches the zig zag will go to the left and make one stitch in the garment fold. The trick is to keep it positioned so that the zig zag gets just a little bit of garment but not too much. The more it catches the more visible it will be on the outside. (The straight stitch will only be visible on the wrong side.)
If you miss a section of the garment you can go back later and stitch again by machine or by hand. But if you miss just one zig zag the hem will probably stay up fine without additional stitching.
Et voila! Here's the right side of the garment. Here I'm using a dark thread so that you can see the stitching but if your thread matches the fabric then you won't be able to see the stitching that much (see below).
This is the hem of these pants. Here I used a white thread and you can see it if you look really closely but from a distance it's invisible. Yay! Let me know if you have any questions. I hope that you find this useful. Happy sewing!