Jeans Part 3: Test Stitching and Tension Adjustments

Before I started sewing my jeans together, the MPB Jeans Sew-Along suggested to test needles, thread and fabric first. Especially since I am using some heavy fabric, and heavy topstitching thread.

Before I began test stitching, I consulted my sewing library for advice. Both the Reader’s Digest Guide to Sewing and DK’s The Sewing Book were silent on the matter of thread tension. I did find some help on adjusting tension in Nancy Zieman’s Sewing A to Z, and in my sewing machine’s instruction manual. So if you need to learn more about thread tension, your machine’s instruction manual would be a great place to start.

Sometimes when checking tension for sewing machine and serger stitches, I find it useful to have a magnifying glass on hand to get a closer look at the stitching. You can see how the top and bobbin threads wrap around each other, as well as how much the bobbin thread shows on the top side, and vice-versa.


For both seaming and topstitching on the jeans project, I am using a #100 denim needle. It’s strong enough to get through the fabric, and the eyelet is large enough to accommodate the heavy topstitching thread.

I am using #80 weight jeans topstitching thread from WAWAK Sewing and Tailoring Supplies (their house brand). I purchased five spools in different colors – red, olive green, navy blue, black, and for this project, “Levi Gold.”


The top tension dial on my machine is numbered from 0 (loose) through 9 (tight). The nominal setting is supposed to be 4. I did a series of test stitches starting at 4, and going up by one number each time. The MPB Sew-Along suggested that a higher top tension would be necessary, to help pull the bobbin thread up through the heavy fabric. Also, the heavy thread will naturally increase the bobbin thread tension. (I didn’t try adjusting the bobbin thread tension, because it’s a teeny tiny screw with no markings and I’m afraid I will screw it up.)

I started with “normal” setting of 4, each row of stitching bumping one number higher.


Topstitching, top thread view. Numbers are tension settings for that line of stitching.


Topstitching, bobbin thread view. Note how the bobbin stitch neatens as top thread tension increases.

Comparing the top thread and the bobbin thread, we see there are some pretty massive differences at the lower tension settings. At 4, the top stitch looks okay, but the bobbin side has all kinds of loose, unsightly loops. As the top tension goes up, the bobbin stitches look tighter and tighter, until at about 8 they more or less match the top stitching. I suspect the best setting is the highest one that gets the stitches on both sides to match, without being so tight the top stitches suffer or the fabric starts puckering. So 8 is the setting I’ll be going with when working with the topstitching thread.

Regular Thread testing

I also use the #100 denim needle for regular seaming. I’m using Gutermann all-purpose thread, in navy blue to match the denim. (For the test, I used white to contrast the denim).

Again, I started out with the “normal” setting of 4, and sewed each row one tension number higher.


Regular thread, top thread view. Tension is ideal up to 6, but is too high after that and pulls the top stitch into a flat line.


Regular thread, bobbin thread view. The bobbin stitches clear up around 6 but don’t improve much after that.


Here, the bottom and top stitches match each other best with the tension set to 6. Above that, the top stitches start to suffer – the tension is so high, they pull up all the bobbin thread, lose their shape, and look like a flat line. So I will use 6 with the regular thread.

Other notes

I haven’t experimented much with more “regular” needle and fabric combinations, say an 80 needle with all-purpose thread on some cotton shirting. But I do suspect the tension settings on my machine might be slightly out of adjustment, for instance a setting closer to “5” behaves a like “4” should. So if you’re following along, and especially if you have the same machine I do, you should do your own set of test stitches to determine the best tension setting for your project.

4 thoughts on “Jeans Part 3: Test Stitching and Tension Adjustments

  1. Matt C.

    Yes, this is the same thing I’ve been doing for my jeans as well… previously I never really touched the tension dial (I didn’t really understand what it does).

    I am getting a better handle on it now though.

    1. mportuesisf Post author

      For most of my early projects, I really didn’t adjust the tension dial at all, just left it at 4. On some projects, I played with tension but didn’t see much difference. This is the first time I’ve systematically experimented with the tension, because the thick topstitching thread and the heavy fabric both seemed like they would need some tweaks to accommodate.

      There’s a three-part video called “The Secret Life of Sewing Machines” on the BrianSews channel on YouTube. Besides being interesting to watch, it has an animated bit that shows how a sewing machine forms a stitch. I think once you have a basic understanding of how the machine forms stitches, you can then have a good sense of how tension might need to be adjusted. Likewise, the book “The Complete Serger Handbook” by Chris James has a great explanation of how tension works with a serger.

  2. Lorna Hill

    I have a commercial machine and I’m using a 18 needle but the thread breaks is so it’s about three stitches and brakes but when I put it on a thin material it looks beautiful and you tell me what I’m doing wrong

    1. mportuesisf Post author


      Some really simple things you want to check and double-check first.

      Starting with needle and thread:

      • Try a different needle, same size. The needle you’re using might be defective in some way, such as burrs or being bent.
      • Are you using the same thread on top and in the bobbin? You should.
      • Are you using cone thread, rather than spool thread? Industrials are meant to use cone thread. Cone thread is wound in cross-diagonals, and the thread unwinds from a cone without twisting when used on industrial-style thread feeds. If you just put a spool of thread on an industrial thread take-up, it will gradually twist while sewing and can cause poor stitches and possibly thread breakage.
      • Is the thread the right size for the needle? If you are using a large-size needle and thread that is too lightweight, this can cause problems. You should be using a heavier weight thread with a size 18 needle.

      Next, check your machine setup and usage:

      • Always make sure the thread take-up lever is always at the top of its travel when you begin or end stitching. Otherwise, the thread can break, or the needle can come unthreaded. This sounds super simple, but it was a problem I had working with industrials (and mechanical sewing machines in general) before I was properly taught how to use them.
      • On your industrial machine, make sure the long groove shaft of the needle faces to the left (towards the left hand side of the machine) when you install the needle.
      • Make sure the bobbin is installed in the case so that it turns clockwise when you are looking at the open side of the bobbin case and pull on the thread.
      • Make sure the bobbin case is installed in the machine with the open notch pointing upwards.
      • Recheck the threading diagram for the top thread. Industrials have lots of little twisty paths the thread must go through, in order to stabilize the thread for high-speed operation. Rethread the machine.

      Next, some things that actually involve tweaking the machine.

      • Next, try checking the top tension. If the top thread tension is too high, the bobbin thread can break.
      • Next, try checking the bobbin tension. You should be able to pick up the bobbin case by the thread, and the bobbin case should just hang on without sliding to the floor. If you give a little upwards tug on the thread, some thread should come out of the bobbin case.

      Adjusting the bobbin thread tension on a commercial machine is pretty much the same as on a home machine. Here’s an article on thread tension that explains how to adjust both top and bobbin thread tension:


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