Going Industrial – Singer 306 series

Really that should be Singer 206 series, but as I don’t own a Singer 206 yet, I will stick to what I know.

Both my Singer 306 and 319 use Type L industrial bobbins, as used in the Singer 206, the Singer 20U range and some earlier machines. They are legitimately industrial bobbins, compared to the 306 and 319 machines which are domestic machines based on industrial beginnings. But they are just a bobbin, nothing really special, a bit higher capacity than others maybe. Part number 55623S.

My Singer 306K is an early model (1954) and is a black and gold model but is aluminium bodied. This means it uses the bobbin case as used in the Singer 206, part number 105032. This case has an “open front” and is located in the bobbin carrier within the hook by pins that register in the open front. My 306K had been well used making sails, so was a little but worn after 70 years, and the bobbin case had issues. As mentioned in other posts, I struggled with lower tension, and decided it was due to a bent tension spring, as it did not sit right around the bobbin case. At great expense I replaced the spring and all was reasonably well for a few weeks. Then one day the bobbin case fell apart due to a metal fatigue break between the slot that the bobbin thread goes through and the open front of the bobbin. Bobbin cases #105032 are getting difficult to find, and none appear to be available here in NZ, so expensive vintage items and even more expensive shipping put me off buying one, especially after spending the same amount on the spring!

I already knew there were alternatives, but most articles seemed to say that the bobbin case had to be modified to be used. But that is not the case if one buys a bobbin case for a Singer 20U (part number 541578, or 410025). This is very similar to the Singer 105032, and is a direct replacement into my 306K (but not all 306 models). This bobbin case has immediate advantages, firstly it is available in New Zealand, and it allows use of 15×1 Universal needles (which already worked anyway). The version I bought is a #541678NBL – where NBL means No Back Lash. Singer 20U machines can stitch at 2000-2500 stitches per minute, and at this speed a fully loaded bobbin would have so much momentum it would run on after reducing the power causing loops and knotting in the hook area. A spring rubs gently against the bobbin, braking it (not breaking) when power is removed.

Since I bought and updated my Singer 319K, I haven’t used my 306K, but it is still there waiting to be put to good use. The motor is only a 0.3amp, so is a bit gutless for heavy work.

My Singer 319K arrived with its bobbin case very badly damaged by needle strike. This needle strike was not caused by using incorrect needles, but by incorrect fitment of the bobbin case into the hook area. If it is not firmly in place, it will vibrate and creep forward in the machine, and the needle will strike the closed front of the bobbin case, damaging the bobbin case and breaking and bending needles. This machine had barely been used, probably because it was never used correctly. I have a Singer 15K110 which was also unused for similar reasons.

To get it going, I took to the bobbin case with a Dremel to clean up the edge of the metal nibbled away by repeated needle strikes, removing a couple of millimeters from the edge of the front, but also widening the arch either side of the open front. My available selection of needles increased because of these changes.

The bobbin case on the 319K is part number 173058, and is used on some 306 machines (not made at Kilbowie). Besides having a closed front, the other main difference is a locating pin in the bobbin carrier in the hook, which is a different position to the 306K, being at the 4 o’clock position. To locate on this pin, the 173058 bobbin case has a slot up the side of the case at the 4 o’clock position to match it. So a 306K bobbin case (105032) or a 20U bobbin case (541678) will not fit into a 319K bobbin carrier and hook.

Incidentally, a lot of this information about the 206 series and their bobbin cases comes from this page from Cyndy Kitt Productions in Australia. A lot of research and work has been done by Cyndy Kitt to detail so much about this subject, and I thank them for it.

I am not happy using this repaired, damaged bobbin case, it is probably as worn as the original 306K case, and is a worry. The machine works great, allows me to use whatever needles I like, and I want to keep that flexibility. The tension is a bit difficult to keep right, so I am looking to replace the original with something newer and better.
I think there are people out there who modify the Singer 20U bobbin case to fit and work on the 319K, but I haven’t found too many details of what the modification is, mainly because I fell out with Facebook and am no longer a member of the groups where I can find this information! It seems fairly obvious to me that if a slot was cut into the bobbin case used on a 20U machine (541678), exactly where the slot is on the 319K bobbin case (173058) it would fit and work just as well.

I have the original 105032 bobbin case with the missing section of the case, and have made some very precise measurements of the position of the slot in relation to the nearest feature on the case that is identical on both cases, namely the slot in the top of the case where the hook that retains the bobbin during placement in the machine slides. From this I created a template in the Inkscape drawing package, and cut the template from self adhesive vinyl on my vinyl plotter. This can be positioned very carefully on the 105032 bobbin case and provides a template that can be attacked with a Dremel grinding tool to reproduce the slot as exactly as possible.

My first example of this fitted straight into the 319K, and hand testing with no thread showed that 206×13 and 15×1 can be used without any interference on the bobbin case. Obviously the original case is broken, and can’t be used for actual sewing, but a new Singer 20U bobbin case has been ordered and I will modify this one and give it a full test.

This is an SVG file of the template 319K bobbin template, you can get the measurements by opening it in a decent drawing package (Illustrator, CorelDraw, Inkscape etc).

A photo of the vinyl template, and a few spares.

A couple of days ago I ordered a new 20U bobbin case from a New Zealand supplier and it arrived today. I actually ordered a Towa version of the bobbin case, it is Japanese made item, rather than the Chinese made generic version. In reality, this is a generic Type L bobbin case, which fits 20u machines along with plenty of others. There are a few part numbers for this item, BCDBZ1NBL6 seems the most common, mine from SewingTimeNZ was BCDBZ3NBL6.
It took a couple of minutes to apply the template to the case, about 5 minutes to carefully cut out the required slot with a Dremel rotary tool. A quick clean up and finishing off with some 600 grit wet and dry to remove the edges and it was ready to go.
It slipped into the machine like a bought one, and the first stitches let me adjust the top tension to match the bottom, and away I went, zig zag stitches at full bight with perfect tension. It really will improve the quality of this machine. Full testing will be done over the next few days, with 4 needle types, and many materials and thread types.

My 306 series machines are both just a little bit more industrial, next step a couple of 1 amp motors to take them to the next level!