I played with my machine settings forever to get a double needle hem that I was happy with. I watched countless YouTube videos and read numerous blogs. I never found one place that summed everything up with pictures. I’m no expert – far from it. But my hems look good now so I wanted to share how!!
My methods may not work for you but I hope they point you in the right direction.
My machine is a Brother CS6000i and I’m using a Klasse Twin Ball Point size 80 (4.0 mm). You’ll want this to be a stretch or ball point twin needle for knits. The narrower your needle the less tunneling you will get.
The set up. You’ll need two spools of thread up top and your bobbin. (If you don’t have a second spool of thread, wind a bobbin and use that.) My machine’s manual came with instructions on how to thread the machine with a twin needle. So I did that. If you don’t have your instructions – google probably has the answer. My machine also comes with a second spool holder seen in the first picture. If you don’t have one, you can improvise by extending your single one with a straw or a small dowel.
You thread your left needle exactly as you would a single needle, then for the right needle instead of putting the thread through the needle guide, you skip that step and just thread the needle – see photo below. (Again, this is machine specific.)
Now the tricky part – getting the tensions and stitch length right. To start, I set my stitch length at a 3.5 and I turn my top tension up to a higher number (varies for different fabric weights). I always always test on a scrap piece first of the same fabric I’m about to hem. This is the result you get. The top stitches look okay but have some tunneling, the bottom is wrong and the stretch is lacking. If you aren’t sure about the result hold the fabric tightly between two fingers (over the stitch) and stretch. If you can feel the thread slipping between your fingers, then you need to work at the settings some more.
The bobbin tension is what is causing this. It’s pulling too tightly on the top threads. The bobbin thread will look more like a straight line than a zigzag when this happens and you will see your top thread as loops on the underside of the fabric.
My machine does not come with a setting to adjust the bobbin tension so I fought this correction for awhile. Once I gave in to fixing the bobbin tension, I got the result I was wanting. There is a screw that needs to be loosened to lower the bobbin tension.
Remove your bobbin case by taking off the plate shown pictured above. When I first inspected my bobbin case there was a green hard goop over the screw so you couldn’t actually see the screw that needed loosening. I used a safety pin and carefully picked the goop out. Then I used a tiny screwdriver to loosen the tension. There are two screws – you will want to loosen the one on the left – the flat head one pictured here.
Now, I can’t tell you how much because it varies per fabric weight but, once you find this screw I promise you will be happier with your twin needle hems. Honestly, the best thing I did was buy another bobbin case. So I keep one at factory settings and keep one loose. That way I don’t have to fiddle with the screw every time I want to hem something – I just swap out the bobbin case. The one on the left has the loosened tension and the one on the right is the factory one.
Results with loosened bobbin tension look much better.
Now, what makes this situation even more awesome is knit interfacing or wash away hem tape. I realize this sounds like extra work. And the last thing you want to do is add another step to your almost completed garment. However, it makes using a twin needle SO much more enjoyable and the results even better. My favorite is Pellon Knit Interfacing (EK130) from JoAnn’s. I pre-cut it into 1/2-inch wide strips (so the stretch is long ways with your strip).
One side of it feels rough and one side is smooth. The rough side goes on your fabric, you iron on the smooth side. Once ironed on, flip your hem up, press, and sew. Wa-la! You can also serge the raw edge before ironing on the hem tape to help stabilize the hem even more.