Tear it down – bobbin case maintenance

What do you do when you’re sewing along and your machine’s tension goes crazy for no reason?

There are the obvious things to do: re-thread the machine, in case the thread “popped” out of one of the guides, or came unseated from the upper tensioner, clean out all of the fluff and lint from the machine, especially in the thread path ( don’t forget the bobbin case area) … sometimes you might even get desperate and clean out the upper tensioner.

If you don’t know how to do that, it’s really straight forward, and can save you a trip to the sewing machine repair shop.

But what do you do if you’ve done all of that and the tension’s still goofy?  Especially if your top tension seems way too tight.  Say you have it turned the upper tensioner all the way loose, and your thread is still laying on the top of your fabric…

Chances are, it’s not the top tension.   Remember, tension is a balance.  We often think only in terms of the upper tension.  Sometimes we even like to pretend that the bobbin tension isn’t there.  Perhaps you’ve even been told to “never touch that!”.  It’s not a hot stove element.  It won’t burn you.  If tension is unbalanced, it can be either that’s wrong.

Consider these statements:

  • Loose Bobbin tension can look like top tension too tight
  • Tight Bobbin tension can look like top tension too loose.

If you’re thinking “But how can bobbin thread tension be wrong?  I never touch it!!”, it’s true.  There’s a way.  🙂  If you use your machine it can and likely will happen eventually.

There is a reason that virtually every sewing machine owner’s manual I’ve ever looked at shows the owner how to adjust the bobbin tension.

Today, we’re going to bond a little with our bobbin tension.  The first thing to do is clean the thread path under the bobbin case spring.  It’s possibly the number one most ignored part of the actual thread path to clean.  Just like your upper tensioner, lint from thread collects in between the bobbin case and the tension spring as it’s pulled through.  It’s unreal how much stuff collects under here.

For this article, we’re using a featherweight bobbin case.  The principle is the same for class 15 bobbin cases, and even the majority of the horizontal bobbin cases I’ve seen (class 66 – 66, 99, 185, 192, 401, 500, etc will be fine with this).  Some of the “ultra” new machines may be set up differently, but the theory is all the same.

Step 1: Rotate the Bobbin Case until you see both of the two tiny screws
FWBobbincase9
Step 2: Turn the right screw (or the one that’s not currently fully tightened.  It’s usually the one closest to the thread when the case is threaded with a bobbin.) until it’s fully seated. Make note of how many turns it is until it’s fully seated. This is your tension adjustment. Counting the turns will let you set it to the same setting as it was before you did this cleaning.  I find as a good guideline about 2/3 or 3/4 of a full turn from fully seated seems to be “average”.
FWBobbincase10
Step 3: Remove both screws carefully, they’re tiny, and they jump! Put them aside for now. The spring will probably fall off, just set it aside with the two screws.

Clean the path where the thread goes.  See the grunge to the right of the second screw hole?  This can hold the spring up, and loosen the tension on the bobbin thread. Remember that “top tension’s too tight” issue above? If the bobbin thread just comes out with the lightest tug (i.e. no tension), it’s going to make the top thread look too tight.
FWBobbincase11
Step 4: Replace the spring, and make sure the curled end is tucked into the hole.
FWBobbincase12
Step 5: I like to tighten the left screw about half way before I install the right screw.
FWBobbincase13
Step 6: Install the Right screw, and tighten then loosen it to the setting you recorded above. Don’t forget to fully tighten the left screw when you’re finished.
FWBobbincase14
Step 7: Now you’re finished!! Time to test sew!
FWBobbincase15

Set your top tension to it’s “usual” setting.  If you find that the lower tension isn’t what it should be, adjust that right screw. Turn it clockwise if it’s a little too loose. A little counter clockwise if it’s a little too tight. Make tiny adjustments, 1/8 turn at a time. Test sew after each adjustment.

The other thing that this procedure is good for is adjusting your bobbin case to use a thread that’s maybe thicker, thinner, slipperier, or more temperamental than the “50 wt mercurized cotton” that your bobbin case was set up to use at the factory.

Thicker thread will require a looser bobbin tension spring because the thread will take up more room and therefore be tighter by default.  Similarly, thinner thread will need a tighter tension spring.

And finally, a picture of your model for this particular tutorial. I bought her with really rough paint.  She’s all ready to be stripped and repainted.  We’re thinking of “Red Bull” blue:

fwdismantled

12 thoughts on “Tear it down – bobbin case maintenance”

  1. I have a Singer 301a. I am trying to repair my bobbin case by following your tutorial. My problem is the left screw is rusted into the bobbin case and the right screw will only come part way out. I am soaking the bobbin case in WD 40. Any ideas on getting out the screws? I have order replacement screws and a replacement spring to use once I get out the screws. Thanks

    1. Likely it will be about patience here. It didn’t seize in a day. It likely won’t come free in a day either.

      Other than that, if the WD40 doesn’t work, you could maybe try Evaporust or Naval Jelly. You should know though that any of those products can lift the plating if it’s not secure anymore and evaporust for sure and possibly the others can chemically blacken items left too long in it.

      When trying to remove the screws, sometimes it’s as much a pushing down on the screw with the driver as turning it to the left.
      It does sound like that case definitely needs some maintenance though.

      1. I was just given this machine yesterday with no manual. It is a Necchi 525FA made in Taiwan. It has a front loading bobbin. The stich length adjustment was stuck. I found online that I could fix that by heating the gears with a hair dryer for 20 minutes. It worked and it did take 20 minutes. Then I turned it on and tested the tension I noticed the bobbin was loose, extremely loose. i tightened it but I could not make a successful drop test. Hold thread bobbin won’t drop, loosen screw a tiny bit bobbin drops like a rock. so I went on the tight side. I put it back and sewed a test line and the bobbin went loose again. I tried again and again but the screw just loosens up. I noticed since, from your page that I didn’t have the top tension threaded right so I tried it again but the bobbin did the same thing. I haven’t yet tried taking the screw out entirely. I did that by accident once on another machine and I was lucky to find where the screw flew to.

        1. It really sounds like you need to follow this post then. Take the screws out over a magnetic sheet. You can get ones that are about the size of a half sheet of paper at the dollar store. One of 3 things is happening:

          1. There’s crud under the spring. This tutorial will help with that.
          2. The spring is bent or damaged. This tutorial will help you evaluate that spring by letting you take it off to better see its condition.
          3 The screw or the screw hole is damaged. Step 2 in this tutorial will tell you if one of those is true here and let you know to replace the screw or the bobbin case. Which one will depend on further inspection of the threads in both parts.

          1. I held it inside a sewing machine case and tried to unscrew it but the screw would not come out. So the screw is probably striped. I can see a line of light on the spring so it appears to be bent. I have a similar bobbin case from a brother machine that has a slightly different spring but it seems to fit in the Necchi so I will use that for now and order a new one.
            When I searched “Necchi bobbin case on” Amazon, the price was $85.00! I searched just “bobbin case” and found one that looks the same for $5.99.
            Even though this machine is over 40 years old I found no lint in it. Maybe the bobbin case was broken from the beginning and they never got around to returning it to the store. It was in a Bernina case.

            1. There’s a good chance your Brother one will do just fine. Make sure the slot where the needle enters the case is the same width or bigger than the original case and you should be fine. It’s a JO1313ZW bobbin case you’re looking for if you want one for each machine.

              It’s likely either a well cared for / serviced just before it was put away machine, or it wasn’t used.

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