Right off the bat, the Roberta has the difference that I do not need to treadle. Instead there are various settings on the speed control, which would relate to treadle speed. I had the advantage that I could keep the speed even, unlike on a non electric spinning wheel. However there is a disadvantage to the Roberta in that it has no way to really tone down the strong pull in created by the bobbin driven set up. Even if I completely remove the tension spring that runs over the flyer, I will still get pull in, due to the bobbin tension always being the same(there is a rubber ring running from the bobbin to the electric motor, speed will change and increase pull in, but even at slow speed there is still a significant pull).
But this is exactly why I wanted to try the experiment with the Roberta, to see just what type of yarn would be spun, trying to keep everything the same except the tension spring. I did do my samples with three different speeds, slow medium and fast. This was a second part of the experiment, I was mainly looking for the ideal speed, given the parameter of increased or decreased tension.
So first I spun my default yarn, both with the tension spring on and off. Both came out to be a 12 WPI 2 ply. These two photos show those samples:
Changing speed made no difference, however I did get a thicker yarn when the tension spring was off, which so far did not match the expected results. It could be because I rarely spin with that tension completely off and it was affecting my spinning.
Next I increased the tension by attaching the tension line and spring and tightening it to the point that the spring was standing taut but not spread open. This increased the pull in dramatically and I immediately was spinning much thicker yarn around 8 WPI. I could get even thicker yarn by increasing the speed, I have the medium speed show here at 6 WPI and got the same thing when spinning at a fast speed (not in photo):
I next reset my Roberta back to how I generally have it set to spin my default yarn. I spun some of that 12 WPI 2 ply, and then started to decrease the tension for a thinner yarn. I completely removed the tension line but was not having much luck creating thin yarn. The next thing to try was to keep the tension spring off and then criss cross the yarn on the bobbin. I saw immediate results, the single thinned out but was not going any thinner than my normal default 12 WPI 2 ply. Here's the photo of all three speeds:
All of the above experiments are based on the premise that treadle speed and drafting stays the same. I finally gave in a split the roving into half of what I had been using, which really thinned the drafting zone. Keeping the other settings the same as above, I finally came up with a very nice even 18 WPI 2 ply.
There's definately proof that yarn diameter can be affected by the increase or decrease of tension. The electric spinning wheel, with it's bobbin driven style may not be the best example of this premise, however I learned so much just doing this simple experiment and now have more skills with the Roberta to spin the type of yarn I want.
Another of my spinning wheels, the Haldane, has had the reputation with me of only being able to spin sock yarn. It is a small wheel, with a small drive wheel which means treadling is often used to compensate for it's lack of range. Likewise it only has two ratios, which I have never understood on a wheel, unless it's just so small that larger ratios would make the operation clunky. But it proved to be the perfect wheel to once again try the tension experiment.
I used the same fiber to keep all factors of the experiment as close as possible. I used a well processed merino top, since I wanted to have a fiber that would draft smoothly and not require me to stop and pick out VM or neps. All the samples were very small, and were created by pulling just spun single off the bobbin and letting it self ply back on itself before measuring the WPI.
First I spun a sample of my default yarn, again a 12 WPI 2 ply. I was spinning on the larger of the two ratios and trying to keep my treadle speed and the drafting the same. I then increased the tension (turn the knob that raises the flyer, tightening the drive band) Of course I felt strong pull in, and also found it was very hard to keep the treadle speed the same, it was much harder to treadle. The yarn thickened up immediately, although it took me a bit of practice to keep the drafting zone even and the twist consistent through out the yarn. The middle sample in the photo below shows my struggle, the bottom sample yarn shows it finally working into a 6 WPI 2 ply:
I reset the spinning wheel back to my default settings and spun some default yarn, and then decreased the tension (still on larger ratio) That yarn is shown as the first decrease tension in photo below which was 14 WPI 2 ply. Then I moved to the smaller ratio and got a finer yarn at 18 WPI (although I had more consistent twist with the larger ratio)
At first I caught myself treadling faster to compensate for the feel of less pull in, but I caught myself doing it and realized I should be keeping the treadle speed the same, and slowed down. I was surprised to find the yarn stayed thin just as before, I just was spinning as much in the same time period.
The last yarn in the photo is an amazing 40 WPI 2 ply that was made after criss crossing the single on the bobbin. It's merino and will relax after sitting, and I just remeasured that WPI as 32 WPI but still, thin is thin!
One comment made in the book is that if you can not go down any more ratios (now true on my Haldane) then you should criss cross the yarn on the bobbin, which is like going down another ratio. I had never tried this on the Haldane, for one thing the way the hooks look on the flyer your first impression is that they are backwards for doing the criss cross. But I found that I really could hook the single on the opposite side and then back to the hook that fed the yarn out the oriface. The only real problem is that the yarn on the opposite side rides very close to the bobbin yarn, it seems to me it could rub as the bobbin fills up.
This angle shows the 'opposite side' on four hooks and then across the bobbin and hooking on the oriface side on three hooks. I found when doing the criss cross, the opposite side is usually on one hook more than the oriface side.
So I have to eat humble pie and no longer say that my Haldane can only spin sock yarn. The wheel is perfectly capable of spinning a lovely lace yarn, as long as I am willing to pay attention and not just sit down and spin my default yarn.
I learned so much from this experiment and I would encourage other spinners to grab some lovely leftover bit of top and try it too with their wheels. You may learn a whole new skill your wheel has, that you never knew.