I use a double needle to hem most of the knits I sew. I love the finish... it looks so professional and just like ready-to-wear clothing. The bobbin thread zigzags between the two needles, giving the hem a bit of stretch, which is just what you want with knits. Using a twin needle is not as scary as it may seem. You can use one on most modern machines and I'm going to show you how! See all my Seam Tutorials here.
Double needles come in a few types, Universal, Denim, Ballpoint and Stretch to name a few. Since I use mine exclusively on knits and I often work with stretch knits (knits with lycra in them), I like to buy the stretch version.
The first number on the packet indicates the spacing between the two needles (in millimetres), and the second number indicates the actual size of the needles. The needle I have on the left is a vintage one that is offset. I've never seen ones in shops like that.
Check through your sewing machine manual to see if it mentions the maximum width of double needle you can use. If there's no mention, then just make sure it fits between the gap in your machine foot and also the needle plate. This is the hole into the bottom of the machine that the needle goes through to make a stitch. See pictures below.
Setting up and Threading Your Machine
First off, remove your regular needle and put the double needle in. Make sure you have the correct foot and needle plate on. Also make sure you have the machine set to straight stitch.
Carefully hand wind the machine to make sure the needle will go through the presser foot and the plate without hitting anything.
Now, we need to thread the machine. I am using different coloured threads to make it easier to see the process, but usually you'd want the threads the same colour.
If your machine has 2 spool holders, put a thread on each. If not, you can piggyback a bobbin on the single spool. If that doesn't work, you can also use a freestanding spool holder or sit your serger near your machine and use a spool holder from that. Or, you can follow this tutorial showing you how to add a second spool holder to your machine using a dowel.
Grab the ends of both threads and hold them as if they are one thread. Thread them through all the points in your machine they same way you thread a single thread.
If your tension disc is visible, thread the separate threads on either side of the disc, otherwise don't worry.
Many machines have two separate thread guides just above the needle, so use one for each thread. If not, put one thread through the thread guide and leave the other free.
If you have an automatic needle threader, sadly it wont work in this case, so manually thread each needle.
Sewing Your Hem
For a neat accurate result, press up your hem the desired amount. You can use a cardboard guide for your hems to get them spot on.
Ideally, you want the raw edge of the hem to fall in between the 2 needles, as shown in the picture above on the right. The raw edge is on the underside of your fabric as you sew, so feel the hem with your hands to make sure it's feeding into the needles in the right spot. Also, use the guides on your machine bed. If you pressed your hem up accurately, this should be enough to keep your hem perfectly even. This is easier to do with the wider double needles. If it doesn't stay between the two needles the whole time that's fine, just make sure it's always catching the hem.
Do a test on a scrap piece of fabric. I need my tension up on 6 to get the desired result, but yours may differ. Once you have the settings you're happy with, sew a small hem on a scrap and then write the settings on it. Keep it in your sewing box.
Now you're ready to hem!
My Tips for Great Results
- Use a longer stitch length. I use about a 3.5 on my machine. Have a little test and see what you like.
- Test your tension. You want the bobbin thread to zigzag between the two needles, with only a minimal amount of the top threads showing through. See picture above.
- You don't need 2 spools of thread the same colour. You can load a bobbin with the thread for your second spool.
- Because the bobbin thread doesn't show through to the front, if you're feeling lazy you can use a different coloured thread in your bobbin.
- Double needles aren't just for hemming knits. They can be used for topstitching on denim and you can create pintucks using a double needle. A narrow one works best, just play with your tension to get the look you want.
- Tunneling - Shown in the picture above, this is when the fabric between the rows of stitching humps up. To fix, try lowering the thread tension.
- Wavy stretched out hem - Try lowering the presser foot tension if you can. A good press can also help so try that first before you start changing your settings. You can also try stabilising the hem fabric with some interfacing or tear-away stabiliser.
- If you're having problems with the threads tangling, try placing the threads on the spool holders so that each spool is unwinding in a different direction.