Spinning Wheels - Understanding How
Single Drive and Double Drive Systems Work

You have seen the phrases:  "single drive with Scotch tension set-up" or "double drive set-up".  What do these terms mean?  How does it affect your spinning? Which is the better system? Below we will talk about both and give you our opinions of each.

Single Drive

Compared to the double drive set-up for spinning wheels,the single drive mechanics are rather new. The introduction of single drive wheels might have come about for the ease of fabricating the parts. 

Single drive mechanics can be of 2 types: flyer lead and bobbin lead.  The difference has to do with what the drive band is driving.  In this section we will talk about the flyer lead system which is what the Kromski single drive wheels and most other manufacturers use.

With single drive wheels, there is a braking system typically referred to as Scotch tension.  So as we talk about single drive here, we are referring to "single drive with Scotch tension braking."

In a single drive set-up, the drive band loops around the drive wheel once and at the flyer it goes around "whorls" or pulleys built into the flyer unit. The pulleys on the flyer are different sizes; it is these different sizes that allow the spinner to control the speed or ratios of the wheel.  Smaller pulleys cause the flyer to rotate faster and the larger pulleys will make the flyer turn slower.  Slower or faster is also affected by how fast  the spinner treadles, so speed is a 2 part equation. Rotation speed at the flyer governs how quickly twist is imparted in the fibers being spun.

In addition to the drive band set-up, there is a braking system that is a critical component, without which take up of yarn can not take place.  A brake band is normally a piece of string that loops over the pulley built into the bobbin. The tension on the brake band can be adjusted with the use of a spring on one end of the band and an adjusting peg on the other. The brake band is designed to create drag on the rotation of the bobbin, retarding its ability to rotate.

Here, in a list format, is what happens when a single drive drive wheel is set up properly:

• foot or feet actuate the treadle(s);
• treadle movement causes footman to rise and fall;
• footman pulls/pushes the crank on the drive wheel axle causing the wheel to rotate;
• the drive wheel rotation will cause the drive band, if tensioned properly, to travel around the circumference of the wheel;
• the moving drive band will cause the flyer mechanism to rotate if properly tensioned;
• when yarn is secured to the bobbin core and routed through the flyer orifice and held securely in a spinner's hands, the flyer and the bobbin will rotate in sync, locked together by the yarn between bobbin and flyer; the brake band on the bobbin pulley is actually slipping to allow this to happen;
• when the spinner allows twisted yarn to advance into the orifice, a degree of tension is released on the yarn allowing the lock of the bobbin and flyer to break;  the rotation of the bobbin will begin to slow as the brake band tension retards speed;  because the bobbin and flyer are now rotating at different speeds, the yarn is pulled from the spinner's hands and is wrapped on the bobbin.

With a single drive wheel, the spinner has 2 separate adjustments that can be made.  First, the tension of the drive band from wheel to flyer - this tension should be just enough  - and no more - to cause the flyer to rotate without slipping when the wheel begins to rotate.  Inappropriate drive band tension is detrimental to the feel of treadling and is to be avoided. Second, the tension of the brake band on the bobbin pulley must be adjusted to set how aggressively the take-up of yarn onto the bobbin feels in the spinner's hand.

Here are some other important aspects of the single drive design.

• the rotation speed of the flyer can be adjusted by placing the drive band on a different diameter whorl groove or by treadle cadence, or both.;
• since the drive band only impacts the positive rotation of the flyer, slipping is not a factor.  This mean that the use of an elastic drive band that grips the flyer pulleys aggressively is a good thing as it allows the tension to be minimal which in turn improves the "feel" at the treadle;
• the material used for the brake band is not terribly important provided it allows for slippage;
• tension on the brake band is affected by the diameter of the bobbin pulley, the thickness of the brake band and the composition of the brake band. Generally speaking, not much tension is needed to retard the bobbin during take-up of yarn.

Double Drive

There was a time when spinning wheels did not have bobbins and flyers.  Yarn was spun on a wheel that had just a spindle.  While  great yarn can be made in this manner, it was a slow process.  Spinners had to do a long type of draw with the wheel rotating one direction, then wind the yarn on the spindle by reversing the wheel direction. Start. Stop. Start. Stop.  A better idea was waiting to be discovered.

And the person to do that was Leonardo da Vinci. The man must have had gears, sprockets and pulleys in his head because he was a born inventor.  So many ideas and so little time.

da Vinci gave some thought to the efficiency of spinning and it may have only taken a short time for him to visualize a mechanical method for allowing a continuous process of spinning yarn without stopping with the ability to store the yarn as production continued. It was all in his mind; he never actually made the devise. Rather, he drew a remarkable sketch which fortunately survived him.  One might imagine him thinking - "I know mechanics and this will work; why make it?"

The job of making the first double drive flyer fell to Johann Jurgen (see page 144) of Germany.

So let's look at the slightly refined double drive flyer we find on modern spinning wheels. (see above picture)

There is virtually no difference in the basic design of this flyer from one wheel maker to the next  In most common practice, a single drive band long enough to loop around the various mechanical parts twice is the drive transmission device.  Think of it doing the same thing the drive belt on a car motor does. Using the energy source of a leg or two, the drive wheel is made to rotate.  The speed of this rotation will impact the driven parts on the spinning wheel. The faster one treadles and the diameter of the drive wheel is one way to control the speed of the driven parts of the spinning wheel, the flyer and bobbin. The drive band is the intermediate part that transfers power from the drive wheel to the flyer.

Everyone can understand the drive wheel.  It is obvious.  But what happens at the flyer? How does the rotation of the flyer and bobbin result in the fibers turning into yarn and being drawn onto the bobbin?

The critical ingredients to this process are the diameter of the whorl (a pulley) and the pulley on the end of the bobbin, coupled with the design/shape of the grooves on the whorl and bobbin pulley. 

The groove(s) on the whorl have a very distinct "V" shape to them, allowing the drive band to sit at the very bottom and grip the sides of the groove.  This gripping is what allows the flyer to be rotated as the drive wheel turns.  There should not be any slipping of the band in the whorl groove - the drive wheel o and the flyer turn together.

Now look at the groove on the bobbin pulley. Properly made, this groove has a "U" shape to it. Unlike the whorl groove, the shape here on the bobbin pulley is designed to allow a certain amount of slipping at important moments during the take-up process while spinning.

Both the whorl and the bobbin are "driven" by the drive band, hence the term "double drive."

Here, in a list format, is what happens when a double drive wheel is set up properly:

• foot or feet actuate the treadle(s);
• treadle movement causes footman to rise and fall;
• footman pulls/pushes the crank on the drive wheel axle causing the wheel to rotate;
• the drive wheel rotation will cause the drive band, if tensioned properly, to travel around the circumference of the wheel;
• the moving drive band will cause the flyer mechanism to rotate if properly tensioned;
• the drive band interacts with both the whorl and the bobbin pulley independently, causing both to rotate if properly tensioned; these 2 parts can and will rotate independently of one another;
• when yarn is secured to the bobbin core and routed through the flyer orifice and held securely in a spinner's hands, the flyer and the bobbin will rotate in sync, locked together by the yarn between bobbin and flyer; the drive band on the bobbin pulley is actually slipping because of the "U" shape;
• when the spinner allows twisted yarn to advance into the orifice a degree of tension is released on the yarn allowing the lock of the bobbin and flyer to break;  the bobbin will begin to rotate faster (because the pulley is smaller in diameter) and it is at this time that yarn, pulled by the bobbin, comes through the orifice and onto the bobbin.

This all happens rather quickly and is difficult to see, but the continuous process of the above steps will result in yarn being made and loaded onto the bobbin.

Tension of the drive band impacts 2 aspects of spinning. First, the rotation of the flyer; second, the force of the take-up of yarn onto the bobbin. In trying to adjust one, you also change the other. Proper tension is thus a balance of these 2 settings. A general rule is this:  with the wheel at rest, you want to be able to pull yarn off the bobbin through the orifice without the wheel turning.  Your final tension may be more or less, depending on other factors. Inappropriate drive band tension is detrimental to the feel of treadling and is to be avoided.

Here are some other important aspects of this design:

• the rotation speed of the flyer can be adjusted by placing the drive band on a different diameter whorl groove or by treadle cadence;
• the diameter of the bobbin pulley, in relationship to the whorl diameter, is critical; as a rule, the bobbin pulley should be a minimum of a third smaller than the diameter of the groove on the whorl for take-up to function. If your bobbin has a pulley on each end, take care that you do not use larger pulley with a small whorl;
• the rotation speed of the flyer impacts how quickly twist is developed in the fibers in the spinner's hand.

Now the question of which is best, or which is best for you. You will forgive us if we do not provide a strong endorsement one way or the other. There are advantages for both systems and trade-offs for each. You will find strong decibels for both systems, with some adamant that one is far superior than the other. Take all of this with a smile on your face, because it is not a case of black and white.

Here are a few of the strong characteristics of each:

Can you make the wrong selection?  We don't think so. A spinner with developed skills should find it easy to use either type of wheel and produce yarn of similar specifications. Further, most wheels are made one way or the other.  So if you like a particular wheel for reasons other than the drive set-up, you must accept that wheel as it comes. Even double drive wheels that offer the ability to set-up in a single drive mode are always a double drive wheel by design, meaning the parts for a double drive will always be there.

Most people will have a bias one way or the other.  If you are new to spinning, we suggest you not fall victim of a teacher or friend who has strong views on this topic.  If you are taking lessons, attempt to use a variety of wheels.  When you find one that is suited to you, that is a good indicator that you will be happy owning such a wheel.

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