Wednesday, May 19, 2021

The Relationship Between Bobbin Tube Diameter and Brake Tension


Last week I wrote about how I finished making resin bobbins for my Electric Eel Wheel Nano -



Aside from wanting to make pretty, see-through bobbins so that my Nano would be as attractive as a traditional, elegant wooden spinning wheel, one of my main motivations for making my own resin Nano bobbins was to try to increase the capacity.


I managed to increase the volume area between the bobbin ends by 13% by using a narrower central tube and removing one of the groove ends.  I was very pleased with this.  13% makes quite a big difference, even on a small bobbin, where every extra millimetre counts.


If you’d like to see how I made my resin bobbin ends, you can read about it here.


As I mentioned in my previous post, the original Nano bobbins have an outer tube diameter that is quite a bit wider than the tube ends that sit on the flyer.  Also, both ends have a groove (which shortens the capacity) when only one groove is necessary.

I asked Maurice why he had chosen to fabricate the Nano bobbins in two parts, when it meant that capacity would be reduced; he explained that this is partly due to the limitations of injection moulding, but it also helps to keep the cost of manufacture down and therefore keeps the Nano at a price that the majority of people would find acceptable.

More importantly, he also said that reducing the size of the tube would increase the need for more frequent tension adjustments.  This last consideration intrigued me.  I’ve been spinning for nearly 30 years, but shamefully, the correlation between how full the bobbin is and how frequently  I need to adjust the tension has never registered with me.  It's only in retrospect that I realise that this fact resonates with me.  I’ve always just spun for relaxation and never gone too deeply into the science involved in spinning.  I decided to take a bit more notice the next time I spun a full bobbin…


I use a spring-tensioned brake band with crimp beads to create small, incremental adjustments to the amount of tension added to the brake band.  This allows me to see exactly how many times I’ve increased the tension on the brake band and to adjust it by a little over 1mm every time. (It also allows me to start a new bobbin with precisely the right amount of tension every time, without struggling to find my ‘sweet spot’.)


Here is my tension band in place before I started filling the bobbin.  I always start with 8 crimp beads below the notch as I know this gives me my ideal amount of light tension.

At this stage, it’s probably worth mentioning that the Nano likes a very light tension, which suits my spinning style perfectly.  Rather than expecting the Nano to pull the fibre out of my hand, I prefer to draft towards the wheel and let the bobbin immediately accept the singles.  If there is any hesitation, and the singles don’t enter the wheel orifice in a perfectly straight line and possibly pigtail up, I know that it is now time to adjust the tension.  N.B. I always check that the yarn hasn’t somehow caught on the yarn guides, or is being hindered in some other way before adjusting the tension.  


For the first time, I decided to take a methodical, scientific approach when I was filling my bobbin to full capacity.  I measured the diameter of the bobbin tube and took a photograph every time I needed to tighten the brake.  I've never paid proper attention to the correlation between bobbin diameter and brake tension and I found the results very interesting. 

Before the first tension adjustment
- 18.7mm bobbin tube diameter
 

I observed just how noticeable the fluctuations in tension were in the early stages of this spin.  In the beginning, I could feel the pull of the singles reducing with every second until I moved the flyer hook along.  In the very early stages of filling my resin bobbin,  the tension was really quite erratic.  It certainly didn’t make me regret making narrower bobbin tubes, but I quickly concluded that Maurice Ribble had found the right balance for the diameter of the original Nano bobbin tubes.  


The Electric Eel Wheel Nano is ideally priced for beginner spinners and I imagine that narrower bobbin tubes would be a cause of genuine frustration to someone just learning to spin.

Before the second tension adjustment
- 28.6mm bobbin tube diameter
 

Once I’d tightened the tension for the first time, and the diameter of the yarn around the bobbin tube widened, the pull of the singles became significantly more restrained.  It felt like I was much more in control of the singles and the spin became much more relaxing.

Before the third tension adjustment
- 49mm bobbin tube diameter

After I’d increased the tension for a second time, I was starting to suspect that the amount of yarn I could get on the bobbin before I needed to adjust the tension was not linear and was increasing exponentially.  The wider the diameter of the yarn on the bobbin tube, the less frequently you need to adjust the brake tension?

Before the fourth tension adjustment
- 63.4mm bobbin tube diameter

However, I was proven wrong on my final tension adjustment when the need to adjust the tension came sooner than expected.  This may well just have been a user based anomaly rather than evidence of scientific fact.  I would have to carry this experiment out repeatedly to know for sure…


Here’s a graph that I’ve plotted that hopefully shows how much more frequent the need for tension adjustments is when the bobbin tube is narrower.  Given that the circumference of a yarn wrap around the bobbin tube increases as the bobbin fills, this is further reason that a wider bobbin tube is almost always desirable.

I would always prioritise bobbin capacity over less frequent tension adjustments, but I hadn’t realised just how much of a difference a thinner bobbin tube would make.   Also, anyone that prefers to spin slightly thicker singles, or doesn’t move the flyer hooks quite as obsessively as I do, would be constantly noticing the variations in tension in the early stages.  The tension would decrease as the bump of fibre built up and then increase again when the hooks were moved along.   I always spin fine singles on the Nano and move the hooks very regularly, so this is not an issue for me, but I imagine that I would be in the minority.


Here's my bobbin when it was just about as full as the flyer arms could accommodate.  There's 104g on there, which is very pleasing.  There's something about getting over that 100g mark that makes me love this little wheel even more!



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