Transcript for

Episode 87:

Wheel Mechanics Mysteries Solved

Do you know why bobbin-led wheels have take-up even if you completely remove the brake band? Do you know why you have to increase the tension on your brake bank as your bobbin fills? I'll be solving these mysteries in this episode!

Hello there darling Sheepspotter! Welcome to episode 87 of The Sheepspot Podcast. I'm Sasha, and my job is to help you make more yarns you love.

I am not a very mechanically-inclined person, and it took me a long time to really understand how spinning wheels work. I think it may have been Henry Ford who said "Whether you think you can or think you can't, you're right." Henry Ford may have been a virulent anti-semite who gave Hitler some of his ideas (true story), but in this case he was actually correct. A lot of the problem was my mindset: I thought I couldn't understand it so I didn't.

But after taking many classes on wheel mechanics with different teachers and doing lots of research, I now understand two things about how wheels work that stumped me for years: why bobbin-led wheels have strong take-up, and why you need to increase the tension as your bobbin fills. I want to issue the caveat here that I am neither an engineer nor a physicist, so I'm going to explain these is as un-technical terms as possible, but here's the best of my understanding. So here goes.

The first mystery has to do with drive systems. Your drive system is the particular way your drive band (the band around your drive wheel) attaches to the flyer/bobbin array. 

Basically, your drive band can turn either the flyer or the bobbin or both. 

In any wheel with a bobbin and flyer (together I'm going to refer to them as the "flyer and bobbin array"), in order for your yarn to take up onto the bobbin, your bobbin and your flyer have to be rotating at different speeds. 

In a flyer-led, or Scotch tension wheel, the drive band is attached to the flyer. In other words it goes around a whorl that is attached to the flyer. So the flyer rotates  at a certain rate as the drive wheel turns. To ensure that the bobbin and the flyer turn at different speeds for take-up, in Scotch tension there's a cord or band over the bobbin to slow it down. While you're spinning, your yarn tethers your bobbin to your flyer (the flyer "leads" the bobbin), but when you release tension on your singles to let the yarn onto the bobbin, the brake band slows the bobbin and voila: take-up happens. 

In bobbin-led, or Irish tension, wheels, the drive band is attached to the bobbin and there's a brake band over the flyer. So while you are spinning, your yarn tethers the flyer to the bobbin, pulling the flyer around as the bobbin rotates. That's why we call these wheels "bobbin-led": the bobbin leads the flyer. When you ease up the tension on your yarn to let the yarn wind onto the bobbin, the flyer slows because it's braked by the brake band.

But if you've ever spun on a bobbin led wheel, like the Louet S-10, you know that even if you take the brake band completely off the flyer, you still get takeup. In other words, you don't actually need the brake band to ensure that, when you let your singles wind on to the bobbin, the flyer and the bobbin are rotating at different speeds. How can that be? 

Well, and I learned this from Alden Amos' Big Book of Handspinning, the flyer wants to go slower that the bobbin anyway. I'm not sure exactly why this is, but I suspect its because the flyer encounters more wind resistance than the bobbin does as it turns. That's why flyer-led wheels always have take-up, whether or not the flyer is actually braked. 

Scotch tension wheels brake the part of the flyer-bobbin array that naturally rotates faster that the flyer, which is why we can dial in the tension so precisely in scotch tension wheels. 

And that's why bobbin-led wheels always have some takeup, brake band or no brake band.

Now, on to mystery #2. If you spin on a scotch tension or double drive wheel, you may have noticed that as your bobbin fills you need to increase the amount of pressure on your brake band. Why is this?

It has to do with inertia. Inertia is a property of matter by which it continues in its existing state of rest or uniform motion in a straight line, unless that state is changed by an external force. Or, as my seventh grade science teacher, Mr. Pecorino, taught me "objects in motion stay in motion, objects at rest stay at rest, and both will resist change."

As your bobbin fills, it gets heavier and it acquires more mass. And the larger the mass, the stronger inertia gets. So the "object in motion" wants to stay in motion, and your full bobbin wants to stay in motion even more that your empty one did. Thus more force (pressure from your brake bank) is required to slow it down. And as we learned in our discussion of mystery #1, you need it to slow down in order for take-up to occur. 

And that's why you need to increase pressure on your brake band as your bobbin fills.

So, today we talked about two mysteries of wheel mechanics that had me stumped for years. I really hope this helped, and if you're a physicist or an engineer, I hope I haven't botched this explanation too badly but please let me know where I've gone wrong if I have. 

There's a post in The Flock, Sheepspot’s free online community for inquisitive handspinners, where you can comment on and discuss this episode if you'd like. I'll link to it in the show notes, which you can find at sheepspot.com/podcast/episode87.

That's it for me this time. I'll be back next time with another episode on my picks for best wheels for new spinners. In the meantime, go spin something. You know it will do you good.