Virtues of Scotch Tension

Previously, I noted that Double Drive (DD) spinning wheels can go faster because they have two drive bands to transmit that power from the drive wheel to the flier assemble. However, you may not really need to go that fast.

If you do not have a real need for speed, “Do you want a DD spinning wheel?” I suggest, not likely.

With DD wheel, the ratio between differential rotation speed (DRS) strongly affects the kind of yarn that you spin. A set DRS can help you spin a very consistent yarn if you are working with the same kind of wool and want to spin miles and miles of the same kind of yarn (production spinning).

On the other hand, if you to work with different kinds of fibers/wools, or you want to spin a different kind of yarn, with a DD wheel you need to change the DRS. This means changing your bobbin or changing your flier whorl or both. If you want to spin different yarns with a DD wheel you need a whole set of bobbins and flier whorls.

Now, some of this can be done by working with a partially filled bobbin to fine tune DRS, and some can be done by adjusting belt tension. However, these steps only take you so far. If you do not have a bobbin/flier whorl combination to give you the DRS that you need for the yarn that you want to spin, you are going to have to fight your wheel for every inch of that yarn that you produce. This takes away from the joy of spinning. This is one reason that people have different DD wheels. Each has a (set of) different DRS, and thus different yarns that they spin easily.

DD wheels come with a very limited selection of bobbin/flier whorl combinations that allow the easy spinning of a very limited number of different yarns. If you have an Ashford Traddy with a (Fast) DD kit, you will find it easy to spin lace singles at about 5,000 ypp. However, spinning 11,200 ypp singles leads to cuss words that cannot be said in public – until you get the right whorl (custom made), and then it goes like butter on warm toast. (Oh, yes, it can be done, but it is not as easy as it is when you have the bobbin/flier whorl combination to produce the correct DRS for that yarn.) If you want to spin 22,400 ypp singles (easily), then you need a different (custom) bobbin/flier whorl combination. Thus, if I want to spin a new kind of yarn, I start by going into the shop and turning a new spinning bobbin that gives me the correct DRS for the yarn that I want to spin. And, when I am spinning ST, I put a lot of yarn on my spinning bobbin. When I am spinning DD, I stop and wind off frequently, because as the bobbin fills, my DRS changes.

Scotch tension (ST) on the other hand will allow you to produce almost any yarn that you want from almost any wool. Small changes in drafting technique, or treadle rate or brake tension are all that is required to easily produce a wide variety of yarns. Thus, Scotch tension is better for people that want to work with a variety of different wools/fibers to produce a variety of different yarns. The downside of ST is that it has lower limits on speed and it is harder to produce a very consistent yarn.

The virtues of DD are ease of producing a consistent yarn very rapidly. The vices of DD are the extreme difficulty of producing yarns for which you do not have an appropriate bobbin/flier combination to produce the correct DRS, and the difficulty of obtaining appropriate bobbin/flier combinations for specialty or unique yarns (particularly for old wheels.)

A New Twist on Lace Fliers

I came to spinning not as a spinner, but as a person interested in yarns that I could not get from commercial sources. As a good student, I asked, “What is the best way to spin fine, high twist singles?” The conventional wisdom that I received was to use a “Lace Flier”.

Lace fliers are Scotch tension flier and bobbin assemblies ostensible designed for the rapid production of lace singles. They tend to be “balanced”, and have low friction bearings to allow them to spin at very high speed. They are flier lead and have small whorls resulting in “high ratios” so that they can turn very fast with a limited treadle rate. Or, at least that is the conventional wisdom.

In fact, at lower speeds (400 – 800 rpm) this is how lace fliers work. As a beginning spinner starts wanting to spin faster, a lace flier helps them insert more twist into their fine singles, and for the beginning spinner, it seems like a lace flier is the ultimate answer to rapidly spinning fine singles.

At slightly higher speeds, things start to fall apart. At low speeds, it takes very little power to drive the flier and bobbin. Windage is minimal. Energy to accelerate the flier is minimal. Energy going into twisting the yarn is minimal. And, (if you oiled your wheel) friction is minimal. However, windage is proportional to the cube of the speed and acceleration is proportional to the square of the speed, with the power dissipated as friction and going into twist being directly proportional to the speed. Together these represent a power consumption function. All the power to the flier is supplied to the flier and bobbin by the drive belt.

Thus, if “windage” consumes 1 watt at 400 rpm, it will consume 8 watts at 800 rpm, 27 watts at 1,200 rpm, 64 watts at 1,600 rpm, and 125 watts at 2000 rpm. This power must be delivered by the drive band. A piece of kitchen string tied with a square knot can easily transfer 8 watts, even if it is sweeping a small whorl. To get that kitchen string to transfer 125 watts (i.e., 2,000 rpm) you are going to have to ply it up into a cable and douse it in a high-friction belt compound, otherwise that belt is going to slip or break. You will be treadling like like crazy, and you wheel will be making all the noises that say it is going fast, but drive belt will be slipping against that little lace flier whorl, so that the flier and bobbin are not going as fast as you think they are going.

Wheel wrights have put great effort into reducing the windage of their lace fliers, but that cubed function for windage is against them. And, in a Scotch tension system, the bobbin cannot go any faster than the flier. In fact, the bobbin speed (and hence twist) will be between 10 % and 30 % less than the flier speed.

The truth is that a high-speed double drive system will provide higher bobbin speed and hence insert more twist into the yarn, allowing faster spinning than a lace flier. There are several reasons for this. Double drive wheels have more than twice as much contact surface with the drive band to transfer more than twice as much power. In a double drive system the bobbin goes 10 % to 30 % faster than the flier. Thus, if you have a Scotch tension wheel and a double drive wheel with the fliers going at the same speed, the double drive wheel will be putting 20 % to 60% more twist into the yarn. I did not know this when I looked at the ratios of various fliers as I prepared to buy my first wheel.

Last summer, I spun 10 miles of 5,600 ypp singles with a lace flier on my Ashford Traddy, and I guessed much of the above. In December, I got a Neiko Digital Tachometer (NDT). That confirmed my worst fears. I was wasting effort. I was treadling and my drive belt was slipping like crazy. (Despite that fact that I have long experience with drive belts in the power range of 0.5 to 800 hp, and I know how to minimize belt slip.) The bottom line is that the small swept area of the lace flier whorl is not capable of handling the power required to drive the flier at much over 2,000 rpm.

The NDT tells me that if I treadle diligently, I can insert a lot more twist into my yarn using the high-speed double drive (ratio stated as 17:1) than I can using the lace flier that Ashford tells me has a ratio of 40:1. For example, the NDT tells me that the Ashford Turbo dive band starts slipping at ~2,000 rpm. It does not matter how much tension I put on it, the band does not drive the Ashford Lace Flier faster, no matter how fast I treadle. From my treadle pace, I think my flier is flying, but the NDT is there to keep me honest.

The NDT tells me that much of what is tossed around about speed of spinning is not accurate. And, it tells me that much of the conventional wisdom about spinning is wrong.



A faster DD bobbin/whorl set for my Traddy that I made by hand.

Moreover, the industry has a odd way of calculating the ratios for DD spinning wheels.  The actual drive wheel/ bobbin ratio affecting spin insertion for the high-speed Ashford DD bobbin/whorl set is closer to 22:1.  The drive wheel/ flier ratio is ~ the stated 17:1, but in practice the bobbin turns faster than the flier, and thus twist insertion is greater than would be expected by comparing the ratios of the DD kit with the ratios of the lace flier kit.

DD is the smart spinner's way to fast twist insertion.