Setting tension for the fabric in front of you
Okay. Last lesson we looked at your stitches and I told you to change your needle more than you think you need to. Good. Now let's talk about tension, because this is the one that makes people want to throw the whole machine off the point of the mountain.
Here's the thing. Tension isn't one setting you find and forget. It's a conversation between your top thread, your bobbin thread, and whatever fabric you happen to have under the needle that day. Denim wants something different than a t-shirt. A t-shirt wants something different than flannel. Change the fabric, expect to check the tension. That's not the machine being difficult, that's just how it works.
What tension actually is
Your top thread runs through a couple of little discs before it gets to the needle. Those discs squeeze the thread, and how hard they squeeze is your tension dial. Your bobbin has its own tension too, a tiny screw on the bobbin case, though most of the time you're adjusting the top dial and leaving the bobbin alone.
When it's right, the top thread and bobbin thread meet exactly in the middle of the fabric. You shouldn't be able to see bobbin thread pulled up to the top, and you shouldn't see top thread dragged down to the bottom. Balanced. Nobody winning.
How to actually test it
Don't guess. Test on scrap, same fabric you're about to sew, same number of layers.
- Thread up, load your bobbin, sew a six inch line on a scrap of the actual fabric you're using for the project.
- Flip it over. Look at the underside.
- If you see loops of top thread sitting on the bottom, or the fabric's puckering, your top tension's usually too loose. Tighten it a notch.
- If the bobbin thread is showing on the top, being pulled up through the fabric, your top tension's too tight. Loosen it a notch.
- Sew another six inches. Check again. Small adjustments. A quarter turn on that dial does more than you'd think.
Write down what number you land on for that fabric. I keep a notebook of every setting for every fabric I've used, dated, so I'm not relearning denim from scratch every single time. Kristin calls it the sewing bible, which I don't think is as funny as she does, but she's not wrong that it saves me time.
The mistake almost everyone makes
People think a bad stitch means a bad machine. Most of the time it means one of three things: old needle, threaded wrong, or tension not set for this fabric. In that order, actually, check the needle first. A dull or bent needle will throw off your tension readings and you'll spend twenty minutes adjusting a dial that was never the problem.
If you've changed the needle, rethreaded from scratch including the bobbin, and you're still getting loops or puckers, then it's genuinely a tension issue and the steps above will fix it.
Fabric changes everything
This is where beginners get nervous about the wrong things. People are terrified of knits and cautious around denim, and I think that's backwards. Denim is honest. It's thick, it holds its shape, it tells you clearly when something's wrong. Knits stretch while you're sewing them, which throws your tension test off if you don't handle the fabric gently and let the machine feed it instead of pulling.
If you're upcycling, which is most of what we're doing in this course, you're going to hit seams with different thicknesses in the same line, a flat part transitioning into a folded hem, four layers of denim where a seam overlaps. Tension that's perfect for two layers can look wrong on four. Don't panic. Slow down over the thick spot, let the machine work, don't force the fabric through.
A quick story, because this is where it clicked for me
I was at Brayden and Jessica's for board game night a while back, and their dining chairs had this sad, worn fabric that had been sad for probably three years. I had leftover upholstery fabric in my bag, because I always do, and at some point in the evening I just got up and started reupholstering two of the chairs. Nobody asked me to. I wasn't even thinking about tension consciously, but upholstery fabric is thick and stiff and totally different from anything I'd been sewing that week, and my stitches came out loose and sloppy on the first chair because I hadn't stopped to test on scrap first. Second chair, I tested. Clean line, no puckering. Same machine, same me, five minutes of testing made the difference.
Measure twice. Test the tension on scrap before you commit to the real seam. Close enough isn't a setting.
Before next time
Grab three different scraps from your project pile, denim, a knit, something in between, and run the six-inch test on each one. Write down where your dial landed for every one. You'll start seeing the pattern.