Once upon a time, singer was the top sewing machine company in the country, if not the world and the had a straight stitch sewing machine in almost every home. For many people, it was the first piece of machinery to enter the house and often existed in places without indoor plumbing and electricity. Having a piece of technology that could rip out a straight seam in minutes instead of hours was revolutionary and the simplicity and quality of those singer machines meant that many things about the sewing machine were standardized with the model 15. Class 15 bobbins, 15×1 needles (130h), and many many other things about sewing machines today are either reactions against or compatibility with the class 15 sewing machine.

These machines were so essential that after ww2, the US government freed up the singer patents and encouraged what industrial capacity existed to create guns and tanks for the japanese army instead turn to sewing machines (it was a common thing for sewing machine companies to make weapons during the war, so tooling off of war machinery and production experience to sewing machines was a matter of swapping out parts and instructions), and so the class 15 clones from japan flooded the market. Singer’s dominance in the sewing machine market was starting to wane and new fabrics were on the rise. 

A class 15 straight stitch only machine has one nemesis: stretchy knit fabrics. A straight stitch thread won’t really work on jersey fabric because the fabric will stretch too far and pop the threads. To keep up with this post-war trend, the japanese machines started to take their straight stitch only machines and add a zig-zag capability. Turns out this ZZ stitch was a killer feature. So what was singer to do? Kluge!

People don’t like the 206 and 306 series machines because they’re ungainly, have louder motors, use weird bobbins AND needles (remember that 15×1 needle comment earlier?) So if you have a 206 or a 306 singer, you’re going to have to find 206×13 needles – and there’s like 3 sizes out there. SO what’s the difference?

bottom to top: 130h standard universal needle, middle is a dbx1 industrial needle, and top is 206×13 needle – Notice how the eyes are about the same length from the top (right side) of the needle, but the point is shorter from the eye to the tip going up the stack? That causes problems.

So here’s how it works with a 206 needle: On the left side of the stitch, the needle goes down to the left of the bobbin opening and the thread gets picked up and worked into the stitch. Then it goes up and back down to the right of the bobbin opening and the thread gets picked up and worked into the stitch. (note that this is as close to bottom dead center [BDC] as i can for this). Now there’s not “Plenty” of space for the thread to work its way about the point, but there’s enough.

Now, when you put in a 130h needle (the kind you can go into any crafts store and buy a 5 pack of), the needle point extends further down and while there is enough space to pick up the thread on the left side of the ZZ, there is just barely not enough space on the right side of the swing for the thread to move freely – (you have to really look at the reflections of the needle in the bobbin to see how close it is)

So! What’s the fix?

 

Well, singer wasn’t exactly in the business of reinventing the wheel when it wasn’t reinventing the wheel, so the timing parts (like everything that ISN’T in these bobbin photos) are the same as other machines that use 130h parts, so you need to find another singer bobbin case for a machine that uses the Class L bobbins (306k uses those instead of class 15 – and you want to keep using the Class L bobbins because the machine’s bobbin winder is geared for class L bobbins), and has a vertical rotary hook. Like 30 years after they released the 306k, they released another rotary hook, class L bobbin machine which WAS compatible with 130h needles – the 20u. So grab a 20u bobbin case and pop it in, right? Almost. If you get part #541678 and attempt to pop it in, you’re going to have trouble: 306k bobbin case on the left, 20u bobbin case on the right. The geometries of the bobbin case allow the needle to clear the bobbin case even if there is a 130h needle point down along side the bobbin.

SO, this is a perfectly functional 306k machine running 206×13 needles, and it runs well on those, so again? Why Infodump? Well, again, 206 needles are VERY HARD TO FIND, which makes them expensive, and limited in cost. Some say run a dbx1 needle which is still made and is still veeeery available in MANY sizes, but… zig don’t zag. So pop in that 20u bobbin, right?

 

Wrong.

This is a 306k bobbin case and shuttle assembly, note that slot along the bottom of the bobbin case?

That fits over a bump which keeps the bobbin case from spinning freely.

Now, if your bobbin case doesn’t have that bump, this style of bobbin not going to fit in at all, instead the 20u bobbin case relies on a different set of bumps to keep it in place: See that ditto lookin’ face in the left pic? That’s what keeps the bobbin case from spinning freely, and the right pic is the shot of those bumps doing their jobs. The good news is that SOME 306k, 306w, and 206 machines come from the factory with 20u compatible shuttles, but if not, you’re gonna have to go to ebay and buy one. 

So, if you’re like me with a 306k or 319 which has the bottom slot style bobbin case, you gotta swap out the shuttle and shuttle assembly if you have the kind with the slot, if not, you can just swap out the 20u bobbin case and be done with it. Assuming you knew how to do that. The simple overview is to remove the screw holding the finger in place and then loosen the screws on the shuttle. assembly shaft to pull it off. If you do that, its a good idea to reset the timing.

The timing sets the eye of the needle relative to the shuttle hook. This is important because the hook hooks the loop caused by the needle retracting upwards 1/16th of an inch. Here’s something really cool about 206×13 and 15x needles – remember how the length from the shaft to the eye is the same and it only differs by eye-to-point length? Well timing is based off of the relationship between the eye and the hook, not the needle. 

 

So, to set the timing, lower the needle to bottom dead center where the timing marker hits the first stop, then rotate the handwheel ever so slightly until you hit the second timing mark. Different machines have different timing marks. On the 15-91 the timing mark is on the needle bar below the head, on the 66/185, etc it’s about the halfway point up the needle bar, on the 306k, it’s on the very top.